Professor Megh Mallavarapu

We determined the distribution, fate, and health hazards of dimethenamid-P, metazachlor, and pyroxasulfone, the effective pre-emergence herbicides widely used both in urban and agricultural settings globally. The rate-determining phase of sorption kinetics of these herbicides in five soils followed a pseudo-second-order model. Freundlich isotherm model indicated that the herbicides primarily partition into heterogeneous surface sites on clay minerals and organic matter (OM) and diffuse into soil micropores. Principal component analysis revealed that soil OM (R2, 0.47), sand (R2, 0.56), and Al oxides (R2, 0.33) positively correlated with the herbicide distribution coefficient (Kd), whereas clay (R2, ¿ 0.43), silt (R2, ¿ 0.51), Fe oxides (R2, ¿ 0.02), alkaline pH (R2, ¿ 0.57), and EC (R2, ¿ 0.03) showed a negative correlation with the Kd values. Decomposed OM rich in C=O and C¿H functional groups enhanced herbicide sorption, while undecomposed/partially-decomposed OM facilitated desorption process. Also, the absence of hysteresis (H, 0.27¿0.88) indicated the enhanced propensity of herbicide desorption in soils. Leachability index (LIX, < 0.02¿0.64) and groundwater ubiquity score (GUS, 0.02¿3.59) for the soils suggested low to moderate leaching potential of the herbicides to waterbodies, indicating their impact on water quality, nontarget organisms, and food safety. Hazard quotient and hazard index data for human adults and adolescents suggested that exposure to soils contaminated with herbicides via dermal contact, ingestion, and inhalation poses minimal to no non-carcinogenic risks. These insights can assist farmers in judicious use of herbicides and help the concerned regulatory authorities in monitoring the safety of human and environmental health. Graphical abstract: (Figure presented.)

Purpose of Review: The synergistic effects of microplastics (MPs) and heavy metals are becoming major threats to aquatic life and human well-being. Therefore, understanding synergistic interactions between MPs and heavy metals is crucial to comprehend their environmental impacts. Recent Findings: The mechanisms such as electrostatic attraction, surface interactions, ion exchange, hydrogen bonding, hydrophobic forces, and p¿p interactions behind the synergistic effects of MPs and heavy metals were critically reviewed and justified. In addition, the roles of surface chemistry in these interactions were also emphasized. Finally, efficient remediation techniques aligning with a circular economy-based initiative to promote sustainable solutions were recommended to mitigate plastic-heavy metal pollution to achieve a cleaner environment. Summary: This review examines the combined impact of MPs and heavy metals in aquatic ecosystems, detailing their mechanistic interactions, and consequences with proposed sustainable solutions. Additionally, this review highlights the MP-heavy metal contamination risks and emphasizes the need for further research to safeguard aquatic life and human health.

Pesticides are the most cost-effective means of pest control; however, the serious concern is about the non-target effects due to their extensive and intensive use in both agricultural and non-agricultural settings. The degradation rate constant (k) and half-life (DT50) of four commonly used pesticides, glyphosate, 2,4-D, chlorothalonil and dimethoate were determined in five Australian urban landscape soils, with varying physicochemical characteristics, to assess their environmental and human health risks. The k values (day-1) for the selected pesticides were inversely proportional to those of organic carbon (OC), silt, clay and Fe and Al oxides, and directly proportional to pH and sand content in soils. In contrast, the calculated values of DT50 (days) of all the four pesticides in five soils positively correlated with OC, clay, silt and oxides of Fe and Al, whereas soil pH and sand content exhibited a negative correlation. The calculated values of environmental indices, GUS and LIX, for the selected pesticides indicate their potential portability into water bodies, affecting non-target organisms as well as food safety. The evaluation for human non-cancer risk of these pesticides, based on the calculated values of hazard quotient¿(HQ) and hazard index¿(HI), suggested that exposure of adults and children to soils, contaminated with 50% of initially applied concentrations, through ingestion, dermal and inhalation pathways might cause negligible to zero non-carcinogenic risks. The present data might help the stakeholders in applying recommended doses of pesticides in urban landscapes and regulatory bodies concerned in monitoring the overall environmental quality and implementing safeguard policies. Our study also clearly demonstrates the need for developing improved formulations and spraying technologies for pesticides to minimize human and environmental health risks. Graphic abstract: [Figure not available: see fulltext.]

Deep decarbonisation pathways can enable the state of New South Wales (NSW) in Australia to reach a net-zero emissions reduction goal and contribute to global mitigation efforts to limit temperature rise to 1.5 °C by mid-century. This paper explores minimum cost solutions for achieving the corresponding greenhouse gas (GHG) emissions reduction target for NSW, using an Australian implementation of the TIMES (The Integrated MARKAL-EFOM System) energy system modelling framework. This paper investigated possible decarbonisation pathways and available technology options to reach the target. It includes both a higher emissions reference case scenario and a scenario implementing the NSW state government's target of net-zero emissions by 2050 under the NSW Climate Change Policy Framework, consistent with the international Paris Agreement on climate change, with available and viable well-developed technologies. The findings show that the NSW energy system can continue its shift from fossil fuels to renewables like solar, wind, and hydro and can entirely phase out coal- and gas-fired electricity generation by 2050. The deployment of zero-emissions technologies along with policy supports are crucial to achieving deep decarbonisation of the NSW economy by 2050. In addition, electrification and energy efficiency improvements play a significant role in the end-use sector's energy consumption reduction in the coming decades. This paper shows that the electricity sector is the dominant contributor to emission reductions up to the year 2030, while transport, buildings, and industry sectors are set to decarbonise later in the projection period (2030¿2050) along this least-cost trajectory. However, the NSW government's aspirational target of net-zero emissions by 2050 can be achieved by 2039 by offsetting negative emissions.

This work assessed the adsorption performance of three common PFAS compounds (PFOA, PFOS and PFHxS) on two water treatment sludges (WTS) and two biochars (commercial biomass biochar and semi-pilot scale biosolids biochar). Of the two WTS samples included in this study, one was sourced from poly-aluminium chloride (PAC) and the other from alum (Al2(SO4)3). The results of experiments using a single PFAS for adsorption reinforced established trends in affinity - the shorter-chained PFHxS was less adsorbed than PFOS, and the sulphates (PFOS) were more readily adsorbed than the acid (PFOA). Interestingly, PAC WTS, showed an excellent adsorption affinity for the shorter chained PFHxS (58.8%), than the alum WTS and biosolids biochar at 22.6% and 41.74%, respectively. The results also showed that the alum WTS was less effective at adsorption than the PAC WTS despite having a larger surface area. Taken together, the results suggest that the hydrophobicity of the sorbent and the chemistry of the coagulant were critical factors for understanding PFAS adsorption on WTS, while other factors, such as the concentration of aluminium and iron in the WTS could not explain the trends seen. For the biochar samples, the surface area and hydrophobicity are believed to be the main drivers in the different performances. Adsorption from the solution containing multiple PFAS was also investigated with PAC WTS and biosolids biochar, demonstrating comparable performance on overall adsorption. However, the PAC WTS performed better with the short-chain PFHxS than the biosolids biochar. While both PAC WTS and biosolids biochar are promising candidates for adsorption, the study highlights the need to explore further the mechanisms behind PFAS adsorption, which could be a highly variable source to understand better the potential for WTS to be utilized as a PFAS adsorbent.

In this study, we compared the genomes of three metal-resistant bacteria isolated from mercury-contaminated soil. We identified diverse and novel MGEs with evidence of multiple LGT events shaping their genomic structure and heavy metal resistance. Among the three metal-resistant strains, Sphingobium sp SA2 and Sphingopyxis sp SE2 were resistant to multiple metals including mercury, cadmium, copper, zinc and lead. Pseudoxanthomonas sp SE1 showed resistance to mercury only. Whole genome sequencing by Illumina and Oxford Nanopore technologies was undertaken to obtain comprehensive genomic data. The Sphingobium and Sphingopyxis strains contained multiple chromosomes and plasmids, whereas the Pseudoxanthomonas strain contained one circular chromosome. Consistent with their metal resistance profiles, the strains of Sphingobium and Sphingopyxis contained a higher quantity of diverse metal resistance genes across their chromosomes and plasmids compared to the single-metal resistant Pseudoxanthomonas SE1. In all three strains, metal resistance genes were principally associated with various novel MGEs including genomic islands (GIs), integrative conjugative elements (ICEs), transposons, insertion sequences (IS), recombinase in trio (RIT) elements and group II introns, indicating their importance in facilitating metal resistance adaptation in a contaminated environment. In the Pseudoxanthomonas strain, metal resistance regions were largely situated on a GI. The chromosomes of the strains of Sphingobium and Sphingopyxis contained multiple metal resistance regions, which were likely acquired by several GIs, ICEs, numerous IS elements, several Tn3 family transposons and RIT elements. Two of the plasmids of Sphingobium were impacted by Tn3 family transposons and ISs likely integrating metal resistance genes. The two plasmids of Sphingopyxis harboured transposons, IS elements, an RIT element and a group II intron. This study provides a comprehensive annotation of complex genomic regions of metal resistance associated with novel MGEs. It highlights the critical importance of LGT in the evolution of metal resistance of bacteria in contaminated environments.

In the present study, we investigated the implication of long-term fertilization of Indian rice paddies with animal manures on the prevalence of veterinary antibiotics (VAs) residues, enrichment of soil microorganisms, and abundance of antibiotic resistance genes (ARGs). The most frequently detected antibiotics in Indian paddy soils were tetracyclines followed by sulfonamides. The soils long-term fertilized with poultry manure (PM) and cow manure (CM) contained significant amounts of VAs (137.20 µg kg-1) in soil. Members of Actinobacteria, Streptomyces, Rubrobacter, Pseudonocardia, Pseudomonas and Rhizobium were predominant in soils that received PM or CM. ARGs such as mtrA, arlR, bcrA, novA, oleC, sul4 and kdpE that confer resistance mostly to macrolides, aminocoumarins, multi-drugs, and sulfonamides were predominant, and the main phyla that contributed ARGs included Actinobacteria (55 %) and Proteobacteria (22 %). Antibiotic modification/degradation was the major (58.30 %) antibiotic resistance mechanism in bacteria enriched in long-term fertilized soils. Residues of tetracyclines, quinolones, sulfonamides, Cu and Cd in soils positively correlated with ARGs. Notably, this study is the first evidence on the prevalence of VAs, antibiotic-resistant microbes, and ARGs in paddy soils of India long-term fertilized with PM or CM and shed light on the interactions between antibiotics, heavy metals and ARGs.

An increasing global population has meant aquaculture, one of the fastest growing food industry sectors, faces significant sustainability challenges as it tries to address the rising global protein demand. In many sectors, production is underpinned by fishmeal as dietary ingredient, but this is a finite resource with competing users from the poultry and livestock industries. Alternatively, some (planktonic) aquatic species, especially brine shrimp Artemia, can be produced using agricultural waste to provide food or biomass to support increasing aquaculture demand. This review investigates research and production of Artemia using agricultural waste. Various systems used for Artemia production in inoculated ponds are analysed and discussed to provide options for environmentally sustainable food systems that can be applied from either an artisanal level in developing countries with a considerable labour force, or in intensive systems in countries with large volumes of under-utilised resources, for example, sugar/alcohol-based waste and inland saline areas. Using agricultural waste, single cell protein production in a separate aerobic digester can be a simple, continuous food source for Artemia to enable daily biomass harvest. This could then be used as a fishmeal replacement or possibly for human consumption to promote a circular economy by remediating waste to produce protein, like a food production mine.

Uptake and accumulation of per- and polyfluoroalkyl substances (PFAS) in Allium cepa from soils amended with biosolids were investigated. The ¿38 PFAS concentrations in soils amended with biosolids ranged from 10.4 to 104 ng g-1 (dry-weight). Among PFAS, perfluorooctanesulfonate (PFOS) concentration was the highest in soils, with a maximum of 48.1 ng g-1, followed by N-ethylperfluoro-1-octanesulfonamidoacetic acid (N-Et-FOSAA) with the maximum of 10.9 ng g-1. The concentration of perfluorooctanoate (PFOA) was higher (0.55¿1.82 ng g-1) in roots of A. cepa than that of PFOS (0.03¿0.13 ng g-1). The accumulation of PFAS in A. cepa shoots depended on the carbon chain length, with a more significant accumulation of shorter C-chain PFAS than the longer C-chain derivatives. The concentration of PFAS in shoots correlated positively with corresponding root concentration, suggesting a significant translocation of PFAS from root to shoots. A. cepa showed no considerable cyto-genotoxicity in the meristem root tip cells exposed to soils amended with biosolids. The oxidative stress parameters such as reactive oxygen species (ROS), mitochondrial membrane potential (MMP), and lipid peroxidation (LP) showed no significant change over control in A. cepa root cells exposed to soils amended with biosolids. The estimated dietary intake for PFOA and PFOS did not exceed the recommended tolerable daily intake (TDI) even after assuming that onion accounted for 100% of vegetable consumption. This study provides evidence of accumulation and translocation of PFAS from soil to roots and shoots of A. cepa. Also, we assessed the potential risk of PFAS accumulated in A. cepa to humans via the food chain to be insignificant.

Aquifers provide integral freshwater resources and host ecosystems of largely uncharacterized, truncated endemic microorganisms. In recent history, many aquifers have become increasingly contaminated from various anthropogenic sources. To better understand the impacts of nitrogen contamination on native groundwater ecosystems, 16S rRNA sequencing of the groundwater microbial communities was carried out. Samples were taken from an aquifer known to be contaminated with nitrogen from multiple sources, including fertilizers and wastewater treatment plant effluents. In total, two primary contaminants were identified: NH4+ (<0.1¿3.7¿26 mg L-1 NH4+ minmedian-max), and NO3- (<0.01¿18¿150 mg L-1 NO3- min-median-max). These contaminants were found to be associated with a decrease/increase in microbial species richness within affected groundwater for NH4+/NO3-, respectively. Important phyla were identified, including Proteobacteria, which had the highest abundance within samples unaffected by NH4+ (36¿81% NH4+ unaffected, 4¿33% NH4+ affected), and Planctomycetes (0.05¿10% NH4+ unaffected, 43¿72% NH4+ affected), which had the highest abundance within the NH4+ affected samples, likely due to its ability to perform anaerobic ammonia oxidation (ANAMMOX). Planctomycetes were identified as a potential indicator for the presence of NH4+ contamination. The analysis and characterization of sequencing data alongside physicochemical data showed potential to increase the depth of our understanding of contaminant behavior and fate within a contaminated aquifer using this type of data and analysis.

Sustainability evaluation of wastewater treatment helps to reduce greenhouse gas emis-sions, as it emphasizes the development of green technologies and optimum resource use rather than the end-of-pipe treatment. The conventional approaches for treating acid mine drainages (AMDs) are efficient; however, they need enormous amounts of energy, making them less sustainable and causing greater environmental concern. We recently demonstrated the potential of immobilized acid-adapted microalgal technology for AMD remediation. Here, this novel approach has been evaluated following emergy and carbon footprint analysis for its sustainability in AMD treat-ment. Our results showed that imported energy inputs contributed significantly (>90%) to the overall emergy and were much lower than in passive and active treatment systems. The microalgal treatment required 2¿15 times more renewable inputs than the other two treatment systems. Addition-ally, the emergy indices indicated higher environmental loading ratio and lower per cent renewa-bility, suggesting the need for adequate renewable inputs in the immobilized microalgal system. The emergy yield ratio for biodiesel production from the microalgal biomass after AMD treatment was >1.0, which indicates a better emergy return on total emergy spent. Based on greenhouse gas emissions, carbon footprint analysis (CFA), was performed using default emission factors, in ac-cordance with the IPCC standards and the National Greenhouse Energy Reporting (NGER) program of Australia. Interestingly, CFA of acid-adapted microalgal technology revealed significant greenhouse gas emissions due to usage of various construction materials as per IPCC, while SCOPE 2 emissions from purchased electricity were evident as per NGER. Our findings indicate that the immobilized microalgal technology is highly sustainable in AMD treatment, and its potential could be realized further by including solar energy into the overall treatment system.

A Gram-positive bacterium, Microbacterium esteraromaticum MM1 able to degrade organophosphorus pesticides such as fenamiphos and malathion, also possessed the ability to degrade high molecular weight polycyclic aromatic hydrocarbon (PAH), pyrene (Pyr) and benzo[a]pyrene (BaP). The strain MM1 degraded 98.7% of initially spiked 100 mg L-1 pyrene within 15 days from the M9 mineral salts medium (pH 7.0) with 0.1% glucose. At optimal pH 7.0, 57.81% of pyrene (100 mg L-1) was degraded as the sole carbon source. In order to determine the influence of carbon sources (glucose, sodium acetate, sodium succinate) and PAHs (Naphthalene (Nap), Phenanthrene (Phe), Benzo[a]pyrene (BaP)) on pyrene degradation, a full factorial design analysis was conducted. Among the carbon sources examined, glucose, sodium acetate, and all the PAHs positively affected pyrene degradation. Interestingly, in the presence of other PAHs, benzo[a]pyrene was degraded by MM1 but not as the sole carbon source. Crude enzyme extracted from MM1 degraded pyrene with the Km and Vmax values of 49.3 µg ml-1 (equivalent to 250 µM) and 9.5 µg ml-1 min-1 mg-1 of crude protein (equivalent to 50 µM), respectively with a specific activity of 0.19 µg ml-1 mg-1 of crude protein. Metabolites such as monohydroxypyrene, 2,6-di-isopropylnaphthalene, and phthalic acid were identified during pyrene degradation by MM1. Differential expression of the protein in the presence of pyrene resulted in the inducement of enolase (phosphopyruvate hydratase) and pyridine nucleotide-disulphide oxidoreductase in MM1. To the best of our knowledge, this is the first report on the degradation of pyrene by M. esteraromaticum MM1.

Acid soils are the degraded (nutrient-poor) soils that generally lack microbial abundance required to promote plant growth. An insight into the microbial diversity in highly acidic soils is crucial from both ecological and environmental standpoints. Previously, we showed that inoculation of acid soils with acid-tolerant microalgae (algalization) significantly improved soil physicochemical and biological characteristics. In the present novel study involving a laboratory microcosm, high-throughput 16S rRNA amplicon sequencing analysis was performed to investigate the bacterial diversity in acid soils algalized with Desmodesmus sp. MAS1 and Heterochlorella sp. MAS3 after 90 days of incubation. Our results on pooled DNA demonstrate that algalization of two acid soils (soil A and B) significantly increased several bacterial genera, and this observation is consistent with Shannon and Chao1 diversity indices. Actinobacteria, Acidobacteria, Firmicutes, and Proteobacteria were the most prevalent phyla enriched in all of the algalized treatments. Interestingly, nonalgalized acid soils favored only Firmicutes and Actinobacteria, but algalization significantly enriched Proteobacteria, Acidobacteria, and Actinobacteria. Canonical correspondence analysis revealed a positive effect of pH in soil A and both pH and organic carbon in soil B on enrichment. Furthermore, soil bacteria of ecological significance that belong to rhizobacteria and diazotrophs, such as Acetobacter, Azospirillum, Bradyrhizobium, Gluconacetobacter, Nitrobacter, Burkholderia, Comamonas, Herbaspirillum, Enterobacter, Nitrosococcus, Brevibacillus, Enterococcus, Frankia, and Anabaena, were greatly enriched in algalized treatments. Thus, we demonstrate here for the first time that algalization of acid soils significantly improves soil health through enrichment of bacteria that are largely implicated in promoting soil health and plant growth

In developing and developed countries, urban gardening has increasingly become an integral part of local food systems for good quality produce, for enhanced urban health and sustainability. There are few gardens with naturally perfect soils for growing plants. However, the soils with poor texture and fewer nutrients can be improved by different types of organic amendments such as composts, garden soils and organic potting mixes that are commercially available in the consumer markets worldwide to promote healthy plant growth. In this study, we assessed 19 different commercially available composts, garden soils, and potting mixes for the presence of 38 per- and polyfluoroalkyl substances (PFAS). The total (¿38) PFAS in the samples ranged between 1.26 to 11.84 µg kg-1 (dry weight). The total concentration of perfluorinated carboxylic acids (¿PFCAs) was higher than that of perfluoroalkyl sulfonic acids (PFSAs) in all products. The total oxidizable precursor assay (TOPA) was applied in the analysis of composts and potting mixes, which revealed an increase in short-chain ¿PFCAs concentrations ranging from 0.48 to 7.63 µg kg-1, which suggested the transformation of PFCAs precursors to short-chain PFCAs. The measured concentrations of short-chain PFCAs after TOPA in the soil substrates have the potential to contribute to plant uptake and food chain transfer of PFAS to humans due to their high mobility.

Pyroligneous acid (PA) is often used in agriculture as a plant growth and yield enhancer. However, the influence of PA application on soil microorganisms is not often studied. Therefore, in this study, we investigated the effect of PA (0.01¿5% w/w in soil) on the microbial diversity in two different soils. At the end of eight weeks of incubation, soil microbial community dynamics were determined by Illumina-MiSeq sequencing of 16S rRNA gene amplicons. The microbial composition differed between the lower (0.01% and 0.1%) and the higher (1% and 5%) concentration in both PA spiked soils. The lower concentration of PA resulted in higher microbial diversity and dehydrogenase activity (DHA) compared to the un-spiked control and the soil spiked with high PA concentrations. Interestingly, PA-induced plant growth-promoting bacterial (PGPB) genera include Bradyrhizobium, Azospirillum, Pseudomonas, Mesorhizobium, Rhizobium, Herbaspiriluum, Acetobacter, Beijerinckia, and Nitrosomonas at lower concentrations. Additionally, the PICRUSt functional analysis revealed the predominance of metabolism as the functional module¿s primary component in both soils spiked with 0.01% and 0.1% PA. Overall, the results elucidated that PA application in soil at lower concentrations promoted soil DHA and microbial enrichment, particularly the PGPB genera, and thus have great implications for improving soil health.

Farmers use wastewater for irrigation in many developing countries, for example Bangladesh, India, China, Sri Lanka and Vietnam because they have limited access to clean water. This study explored cadmium (Cd) bioaccumulation in two spring wheat cultivars (cv. Mustang and Lancer), which were grown in different concentrations of Cd (0,1, 2, 4, and 8¿mg kg-1) in agricultural soils. The half maximum inhibitory concentration (IC50) values were 4.21 ± 0.29 and 4.02 ± 0.95, respectively, whereas the maximum health risk index (HRI) was 3.85 ± 0.049 and 5.33 ± 0.271, respectively, for Mustang and Lancer. In other words, the malondialdehyde content increased significantly in Mustang (around five-fold) and Lancer (around four-fold) compared with the control treatment. Results revealed that Cd content was well above the acceptable limit (HRI >1) in the two cultivars when exposed to different levels of Cd stress. The tolerant cultivar (Mustang) has potential to chelate Cd in the nonedible parts of plants in variable fractions and can be used efficiently to improve growth and macro- and micro-nutrients content while reducing Cd concentration in plants in Cd-contaminated soil. It can also diminish the HRI, which may help to protect humans from Cd risks. The two cultivars¿ nutrient availability and sorption capacity significantly shape their survival and adaptability under Cd stress. Based on what is documented in the current study, we can conclude that Mustang is more tolerant and poses fewer health hazards to people than Lancer because of its capacity to maintain grain macro- and micro-nutrients under Cd stress.

Food contamination with pesticide residues is a serious concern, particularly in developing countries. The study analyzed samples of country bean (Lablab purpureus L.) and yard long bean (Vigna unguiculata L.) for residues of widely used insecticides to ensure food safety. We used a modified quick, easy, cheap, effective, rugged, and safe (QuEChERS) extraction method followed by gas chromatography (GC)-flame thermionic detector (FTD) for quantitative estimation of pesticide residues. Mostly, the residues of chlorpyrifos, dimethoate and quinalphos were found in 11 and 14 % of country bean and yard long bean samples, respectively. About 50 % of the insecticide-contaminated bean samples contained residues above the maximum residue limit (MRL), which warrants a caution about the extensive and intensive use of pesticides in modern agriculture. The general claim of pesticide adulteration could contribute to the widespread occurrence of several insecticides in beans that threatens food safety. The assessment for chronic non-cancer health risk, based on estimated daily intake (EDI) and hazard quotient (HQ), suggests that the consumption of insecticide-contaminated beans poses potential threat to the health of adults (EDI: 2.79 × 10-4¿2.96 × 10-4 and HQ: 0.56¿0.59) as well as children (EDI: 9.79 × 10-4¿1.77 × 10¿3 and HQ: 1.96¿3.55). Overall, our results clearly indicate that around 50 % of insecticide-contaminated bean samples, available at various local markets in Bogura district of Bangladesh, may cause health risks in humans. The present observations might help the regulatory authorities concerned in setting new guidelines for the limits of pesticide residues in commonly used bean vegetables, and in monitoring the quality of commercial formulations.

Soil enzymes secreted by microorganisms play a critical role in nutrient cycling, soil structure maintenance, and crop production. However, understanding of the linkage between soil enzyme kinetics and microbial metabolism and active microbial communities is remarkably limited. In this study, we measured the kinetics of three hydrolase enzymes, active microbial abundance and substrate-induced respiration (SIR) from 21 farmlands differing in their fertilities collected from the Loess Plateau, China. Results showed the high fertility soils had higher total organic carbon (TOC) and nutrient contents, potential microbial activity, the colony-forming units (CFU) of actinomycetes, and values of enzyme Vmax and Km than those of low fertility soils. We also observed that the CFU of fungi and other bacterial groups did not change with soil fertility status. Soil chemical properties explained 74.0% of the variance in Vmax and 28.3% of the variance in Km, respectively. Whereas, the abundance of main microbial groups and fungi/bacteria ratio only explained 10.2% and 7% of the variance of Vmax and Km, respectively. The interactive effect of soil properties and microbial community could explain 20.2% of the variance in Km. Our results suggest that the substrate availability would mainly drive enzyme kinetics compared to the abundance of active/potentially active microbes in the farmland soils.

Fluorescein diacetate hydrolase (FDA¿H) is an accurate biochemical method measuring the total microbial activity in soil, which indicates soil quality under ambient environmental changes such as pesticide parathion (PTH). However, the influence of PTH on the kinetics of FDA¿H is still unknown. In this study, fifteen farmland soils were exposed to acute PTH pollution to investigate how the kinetic characteristics of FDA¿H change with PTH concentration. Results showed that PTH strongly inhibited the FDA¿H activities. The values of maximum reaction velocity (Vmax) ranged from 0.29 to 2.18 × 10-2 mM g-1 soil h-1 and declined by 42.30%¿71.01% under PTH stress. The Michaelis constant (Km) values ranged between 2.90 and 14.17 × 10-2 mM and exhibited three forms including unchanged, increased (38.16¿242.65%) and decreased (13.41¿39.23%) when exposed to PTH. Based on the changes in two kinetic parameters, the inhibition of PTH on FDA¿H was classified as three types, i.e., noncompetitive, linear mixed and uncompetitive inhibition. The competitive inhibition constant (Kic) and noncompetitive constant (Kiu) ranged from 0.064 to 0.447 mM and 0.209 to 0.723 mM, respectively, which were larger than the Km in values. The catalytic efficiency (Vmax/Km) of FDA¿H is a sensitive integrated parameter to evaluate the PTH toxicity due to the higher inhibition ratio than the Vmax. The PTH toxicity to FDA¿H decreased with increase of soil organic matter and total nitrogen contents. This implied that the PTH toxicity could be alleviated by an increasing content of soil organic matter due to its buffering capacity to PTH. Besides, soils with a higher content of total nitrogen could provide stable environment for FDA¿H to maintain its functionality under PTH pollution. Thus, the results of this study have great implications to the risk assessment of parathion in soils.

Widespread environmental contamination of per- and polyfluoroalkyl substances (PFAS) is well established. Nevertheless, few studies have reported on the aquatic toxicity of PFAS, especially in indicator species such as Daphnia. In this study, the toxicity of two major PFAS, namely perfluorooctanoic acid (PFOA) and perfluorooctanesulfonate (PFOS), was investigated on water flea (Daphnia carinata) using a battery of comprehensive toxicity tests, including a 48 h acute and a 21-day chronic assays. The survival, growth, and reproduction of D. carinata were monitored over a 21-day life cycle. PFOS exhibited higher toxicity than PFOA. The 48 h LC50 values (confidence interval) based on acute toxicity for PFOA and PFOS were 78.2 (54.9¿105) mg L-1 and 8.8 (6.4¿11.6) mg L-1, respectively. Chronic exposure to PFOS for 21 days displayed mortality and reproductive defects in D. carinata at a concentration as low as 0.001 mg L-1. Genotoxicity assessment using comet assay revealed that exposure for 96 h to PFOS at 1 and 10.0 mg L-1 significantly damaged the organism's genetic makeup. The results of this study have great implications for risk assessment of PFOS and PFOA in aquatic ecosystems, given the potential of PFOS to pose a risk to Daphnia even at lower concentrations (1 µg L-1).

This study focuses on the conversion of biosolids to biochar and its further use in adsorbing per- and polyfluoroalkyl substances (PFASs) from contaminated water. In particular, this study aims to (a) investigate the performance of a semi-pilot fluidised bed pyrolysis unit in converting biosolids into biochar, (b) examine the ability of the pyrolysis-combustion integrated process to destruct PFASs present in biosolids and (c) study the application of biosolids derived biochar for removing PFASs from contaminated water. The semi-pilot fluidised bed pyrolysis unit demonstrated stable temperature and oxygen profiles in the reactor. The yield of biochar was found to be 36-45% at studied temperatures (500-600 °C). The produced biosolids derived biochar samples, due to their lower H/C and O/C ratio, were found to be extremely stable with an expected long (millennia) residence time in soil. It was concluded that >90% removal of perfluorooctanesulfonate (PFOS) and perfluorooctanoic acid (PFOA) from biosolids derived biochar could be achieved in the pyrolysis-combustion integrated process. The biosolids derived biochar demonstrated >80% adsorption of long-chain PFASs and 19-27% adsorption of short-chain PFASs from PFAS contaminated water. This journal is

The accumulation of microplastics (MP) in soil via their continuous release and degradation of large plastics has recently become a serious global problem. The major concern with MP is their potential to sorb pollutants as well as ingestion by living organisms. Hence, this study focused on the effect of PVC MP exposure on increasing the risk of perfluorooctane sulfonate (PFOS) and perfluorooctanoic acid (PFOA) bioaccumulation in earthworms in addition to their reproduction. In general, the bioaccumulation factor (BAF) for PFOA and PFOS increased up to 200% in earthworms exposed to MP-contaminated soil. MP at 500 and 1000 mg kg -1 soil caused enhanced uptake of PFOS and PFOA in earthworms, and a significant reduction in their reproduction. These results have significant implications for risk assessment of MP in soil.

Nitrogen contamination of groundwater and the environment is an increasing problem in today's society. Since the invention of the Haber-Bosh process in 1913, the impacts of N on human health and the environment have become increasingly widespread due to the industrial scale production of reactive N (Nr). As a result, government organisations and the scientific community continue to make advances towards tackling this ongoing problem. The inherent difficulties of accessing, observing and monitoring groundwater, combined with the complexity of interactions between groundwater chemistry, hydrogeology and ecology have resulted in gaps in fundamental knowledge, specifically regarding the understanding and remediation of N contaminated groundwater. As these knowledge gaps are addressed with ongoing research, current and future remediation targets are being consistently updated; this has resulted in past remediation strategies that may no longer be consistent in meeting new regulatory guidelines for water quality. As such, the search for more technically and economically feasible remediation strategies continues. Recent advances in bioremediation technologies have opened up promising avenues for research in the remediation of N contaminated groundwater. This literature review outlines the past, present and future of Nr-contamination and remediation in Nr -contaminated groundwater within the broader context of the larger environment. The literature cited in this review is critically evaluated to determine significant knowledge gaps.

Arsenate [As(V)], in general, is associated with various aggregates and exists as different species in soil, which in turn influences its toxicity and potential contamination. Previous studies have demonstrated the usefulness of alkaline phosphatases (ALP) to evaluate As(V) pollution. However, the effect of different arsenic fractions on ALP among soil aggregates is still unclear. Thus, the distribution of As fractions and ALP kinetics was determined in four-month As-aged paddy soil aggregates. Results revealed the two major fractions of As in aggregates were humic-bound and Fe and Mn oxides-bound [both around 30% under 800 mg kg-1 of As(V)]. Besides, it was observed that available soil phosphorus could positively affect the relative content of water-soluble, exchangeable and carbonate-bound arsenic. In the kinetics experiment, both the Michaelis-Menten constant (Km) and maximum reaction velocity (Vmax) of ALP increased with increasing As(V) concentration under four months ageing for each size aggregate. Multiple linear stepwise regression analysis between kcat and the relative content of arsenic fraction indicated that carbonate-bound arsenic is the main fraction that inhibited the kcat for macroaggregates (> 0.25 mm size). For soil aggregates of 0.1¿0.25 mm size, kcat increased with an increase in arsenic residual fraction. As for aggregates <0.1 mm size, Fe and Mn oxide-bound fraction is the main fraction that inhibited the kcat. Overall, this study suggests carbonate-bound and Fe and Mn oxide-bound arsenic fractions could decrease the ALP activities via a decrease in the catalytic efficiency in macroaggregates and <0.1 mm size aggregates, respectively. Besides, available phosphorus should be considered as the main factor when assessing As biotoxicity and mobility.

Tolerance of the three metals cadmium (Cd), copper (Cu), and zinc (Zn) by four microalgal species was investigated in three different culture media available in the literature together with a modified version in order to study the effect of growth media components in estimating the bioavailability of metals introduced into the medium. The free metal content of each medium was also determined using Visual MINTEQ version 3.1 to compare the bioassays. Four microalgal isolates were identified as Desmodesmus sp-I, Desmodesmus sp-II, Coelastrella sp., and Chlorella vulgaris. The present work demonstrated that the microalgal media components have a profound effect on the bioavailability of the metals in the media, so that the bioassay results may vary depending on the growth medium used in the experiments. Furthermore, the free metal contents in each media varied depending on the concentrations of metals added. The tolerance of microalgae evaluated as 50% effective concentration (EC50) of metals differed significantly (p < 0.05) depending on the growth medium used and also varied between the species of the same genus. Desmodesmus sp-I showed high sensitivity to Cd (EC50 0.220 ± 0.011¿mg L-1) and Zn (EC50 0.464 ± 0.065¿mg L-1), whereas Desmodesmus sp-II showed high sensitivity to Cu (EC50 0.098 ± 0.002¿mg L-1) when grown in Test Medium 1 (TM1). The Chlorella vulgaris strain was found to be the most resistant microalga among the four isolates tested in this study. This study has significant implications for the risk assessment of these metals using algal bioassays.

Arsenate (As (V)) is a highly toxic species of arsenic (As) which is also an excellent phosphate analogue. Plant species that are adapted to phosphorus (P) impoverished soil display a negative response to elevated phosphate due to an inability to downregulate P acquisition. Despite widespread As contamination and shared transport systems for As (V) and P uptake, little to no information is available on the response of P-sensitive plants to As (V). The aim of the study was to investigate the response of P-sensitive plants to As (V). One high (Hakea prostrata R.BR) and one moderate (Banksia seminuda B.Rye) P-sensitive species and one vegetable plant species (Cucumis sativus L.) were grown in nutrient solution containing different As (V) concentrations. Based on EC50 data from nutrient culture, Hakea prostrata was the most sensitive species to As (V) followed by B. seminuda and C. sativus. Critical exogenous concentrations of As that reduced plant growth by 50 % (EC50) in H. prostrata, B. seminuda and C. sativus were respectively 0.64, 0.76 and 1.08 µM for shoot and 0.66, 0.51, 1.07 µM for root. Hakea prostrata had the highest translocation factor (ratio of As concentration in shoot to root) of 0.11, followed by B. seminuda (0.03), and C. sativus (0.01). Plant species with high and moderate P sensitivity were associated with high sensitivity to As (V) exposure and accumulation in shoots. The increased sensitivity has important implications in ecological risk assessment and selection of plant species for rehabilitation. The impacts of As(V) at low P levels in soil solution is needed to inform contaminated site assessment and rehabilitation.

Acclimatory phenotypic response is a common phenomenon in microalgae, particularly during heavy metal stress. It is not clear so far whether acclimating to one abiotic stressor can alleviate the stress imposed by another abiotic factor. The intent of the present study was to demonstrate the implication of acidic pH in effecting phenotypic changes that facilitate microalgal tolerance to biologically excess concentrations of heavy metals. Two microalgal strains, Desmodesmus sp. MAS1 and Heterochlorella sp. MAS3, were exposed to biologically excess concentrations of Cu (0.50 and 1.0 mg L¿1), Fe (5 and 10 mg L¿1), Mn (5 and 10 mg L¿1) and Zn (2, 5 and 10 mg L¿1) supplemented to the culture medium at pH 3.5 and 6.7. Chlorophyll autofluorescence and biochemical fingerprinting using FTIR-spectroscopy were used to assess the microalgal strains for phenotypic changes that mediate tolerance to metals. Both the strains responded to acidic pH by effecting differential changes in biochemicals such as carbohydrates, proteins, and lipids. Both the microalgal strains, when acclimated to low pH of 3.5, exhibited an increase in protein (< 2-fold) and lipid (> 1.5-fold). Strain MAS1 grown at pH 3.5 showed a reduction (1.5-fold) in carbohydrates while strain MAS3 exhibited a 17-fold increase in carbohydrates as compared to their growth at pH 6.7. However, lower levels of biologically excess concentrations of the selected transition metals at pH 6.7 unveiled positive or no effect on physiology and biochemistry in microalgal strains, whereas growth with higher metal concentrations at this pH resulted in decreased chlorophyll content. Although the bioavailability of free-metal ions is higher at pH 3.5, as revealed by Visual MINTEQ model, no adverse effect was observed on chlorophyll content in cells grown at pH 3.5 than at pH 6.7. Furthermore, increasing concentrations of Fe, Mn and Zn significantly upregulated the carbohydrate metabolism, but not protein and lipid synthesis, in both strains at pH 3.5 as compared to their growth at pH 6.7. Overall, the impact of pH 3.5 on growth response suggested that acclimation of microalgal strains to acidic pH alleviates metal toxicity by triggering physiological and biochemical changes in microalgae for their survival.

The ageing of a contaminant in soil influences the bioavailability and toxicity of environmental pollutants. Yet, despite arsenic (As) being an important terrestrial contaminant, the effect of As ageing on phytotoxicity has received relatively little research. Research to date has reported predominantly short term (< 0.5 years) experiments. Here, we studied the influence of ageing over 0.25 and 5 years on the phytotoxicity of As (as arsenate) on Cucumis sativus L. (cucumber). The study showed that increasing ageing time of As from 0.25 to 5 years increased the EC10 and EC50 values by 4.0 and 1.76 fold, respectively. The dependence of ageing on soil properties was also examined, although only Freundlich sorption parameters were correlated to the ageing factor (r = 0.68, P = 0.028). Soils with high adsorption capacity also showed the greatest change in toxicity over 5 years. In addition, data was compiled from relevant literature to develop a model for As ecotoxicity. The combined model (n = 54) showed no relationship with pH but was correlated to the oxalate extractable iron content and %clay. Arsenate ecotoxicity (EC50, mg/kg) in the multivariate model was related to oxalate iron content, %clay and ageing time. Thus, the results of this study have significant implications for risk assessment of long-term As contaminated soils.

Microplastics are among the ubiquitous contaminants in our environment. As emerging contaminants, microplastics are still facing with lots of challenges on the characterisation, including their capture, identification and visualisation, particularly from a complex background. For example, when we print documents using a laser printer, we are printing microplastics onto paper, because the plastics are the main ingredient of the toner powder mixture. Characterisation of these microplastic mixture meets an even more complicated challenge, because plastic's signals might be shielded by other toner powder ingredients such as the pigments, the dyes, the black carbon, and the paper fabrics as well. To solve this challenge, we employ various techniques, including SEM, TEM, XPS, FT-IR, TGA and Raman, to characterise the microplastics printed via the toner powders. Interestingly, we show that Raman can distinguish and visualise the distribution of the microplastics from the complex background of the mixture. We estimate the millions of toner powders, each of which is ~4¿6 µm in size, are printed out per A4 sheet as microplastics. The findings send a strong warning that millions of microplastics might be generated from the printing activities in our daily lives.

A Green fluorescent protein (GFP) based whole cell bacterial biosensor was prepared using a bacterial strain sensitive to several heavy metals in order to detect bioavailable heavy metals in soils. The transformant, named as Bacillus megaterium VR1 was immobilized in silica matrix using sol¿gel technology, and optimized for its effective pH range, cell density, exposure time, and storage stability. The lowest detection limit (LOD) for each metal was also determined. The pH range for the bacterial strain was found to be between pH 5¿8.5. The optimum exposure time for the transformed bacterial strain to respond to the lowest tested concentration of heavy metal at 25% of inhibition compared to the control was determined as 4 h, 4 h, and 7 h, for Cd, Cu and Zn, respectively. SiNa/LUDOX 1/1 was selected as the optimum immobilization matrix. Storage up to 2 weeks did not show any reduction in the fluorescence in all the matrices. The linear range of the whole cell bacterial biosensor was determined as 0-10; 0¿20 and 0¿100 mg/L for Cd, Cu and Zn respectively. The lowest detection limit was determined as 1.42 × 10-4, 3.16 × 10-4, and 2.42 × 10-4 mg/L for Cd, Cu and Zn, respectively.

Nitrogen amendment is known to effectively enhance the bioremediation of hydrocarbon-contaminated soil, but the nitrogen metabolism in this process is not well understood. To unravel the nitrogen metabolic pathway(s) of diesel contaminated soil, six types of nitrogen sources were added to the diesel contaminated soil. Changes in microbial community and soil enzyme genes were investigated by metagenomics analysis and chemical analysis through a 30-day incubation study. The results showed that ammonium based nitrogen sources significantly accelerated the degradation of total petroleum hydrocarbon (TPH) (79¿81%) compared to the control treatment (38%) and other non-ammonium based nitrogen amendments (43¿57%). Different types of nitrogen sources could dramatically change the microbial community structure and soil enzyme gene abundance. Proteobacteria and Actinobacteria were identified as the two dominant phyla in the remediation of diesel contaminated soil. Metagenomics analysis revealed that the preferred metabolic pathway of nitrogen was from ammonium to glutamate via glutamine, and the enzymes governing this transformation were glutamine synthetase and glutamate synthetase; while in nitrate based amendment, the conversion from nitrite to ammonium was restrained by the low abundance of nitrite reductase enzyme and therefore retarded the TPH degradation rate. It is concluded that during the process of nitrogen enhanced bioremediation, the most efficient nitrogen cycling direction was from ammonium to glutamine, then to glutamate, and finally joined with carbon metabolism after transforming to 2-oxoglutarate.

Organic farming for higher ecological and human health benefits has been adopted in about 186 countries, covering a total area of 71.5 Mha worldwide. Because of the associated practices, the flows of several environmental pollutants into the organic products threaten food safety and human health. The contaminants that occur at higher concentrations in organic produce include persistent organic pollutants (61.3¿436.9 ng g-1 lamb meat, and 0.28 pg g-1-2.75 ng g-1 bovine meat), heavy metals (0.5¿33.0 mg kg-1 lettuce), organochlorine pesticides (11¿199 µg g-1 carrots), cyclodienes, hexachlorocyclohexanes, hexabromocyclododecane (2¿3 times higher than in conventionally produced porcine meat), hexachlorobenzene (1.38¿14.49 ng g-1 fat in milk), and non-brominated flame retardants (1.3¿3.2 times higher than in conventional produce of greenhouse-grown tomato and cucumber). Moreover, some pollutants like per- and polyfluoroalkyl substances with a longer half-life (1.50¿9.10 yrs) are reported to occur in several organic products. In fact, several legacy persistent organic pollutants are known for their significant trophic magnification in an urban terrestrial ecosystem. In addition, many plant functionalities are adversely affected in organic farming. Therefore, the long-term usage of organic products containing such pollutants poses a significant threat to human health. The major limitation in organic livestock production is the severe shortage of organic feed. Several variable standards and technical regulations set by the government and private agencies are the major obstacles in the global marketing of organic products. The present review critically addresses the impact of organic farming on hidden risks due to the use of composts as the amendment resources that enhance the phytoaccumulation and trophic transfer of pollutants, the functional diversity of the ecosystems, and poor harmonization among the policies and regulations in different countries for organic farming. The future directions of research have been suggested to mitigate unintended flows of pollutants into the organic products.

Total oxidisable precursor assay (TOP assay) can degrade and convert ¿unknown¿ per- and polyfluoroalkyl substances (PFAS) to detectable PFAS. However, the detailed degradation pathway is still not known, particularly when the TOP assay is applied to analyse complex samples such as aqueous film-forming foam (AFFF). To gain insights into the pathway and the effectiveness of the TOP assay, several ¿known¿ compounds are first tested as controls, including sodium dodecyl benzene sulphate (SDBS), perfluorooctanoic acid (PFOA), perfluorooctanesulfonic acid (PFOS). Secondly, the test is expanded to several PFAS precursors such as 6:2 fluorotelomer sulfonate (6:2 FTS), 8:2 fluorotelomer sulfonate (8:2 FTS), and a cationic surfactant N-ethyl-N-(2-hydroxyethyl) perfluorooctyl sulfonamide (EtFOSE). Thirdly, the TOP assay is used to test ¿unknown¿ PFAS samples that have been previously used as AFFF in Australia. The degradation products are monitored, to compare the mass balance and propose the degradation pathway. While HPLC-MS/MS is typically employed to detect the individual TOP assay products, most of which are perfluoroalkyl carboxylic acids (PFCA), an app-based smartphone sensor can also provide semi-quantitative results as a sum. Overall, the results indicate the effectiveness of the TOP assay to assess the presence of PFAS precursors in the AFFF samples, with some variations in the end products. Recommendations for enhancement of the TOP assay are also provided.

Perfluorooctanoic acid (PFOA) is a prevalent, persistent organic pollutant (POP) in the environment. The potential toxic impacts of PFOA on human and ecological health is becoming an increasing concern worldwide. In this study, we investigated the acute toxicity of PFOA in terms of growth, mortality, lifespan, neurobehaviour, fecundity and livelihood in Caenorhabditis elegans (C. elegans), a free-living ecologically important animal model species. The acute toxicity (LC50) of PFOA was found to be 4.42 µM (1.83 mg/L). PFOA exposure induced alteration in locomotor behaviour in C. elegans. The reproduction capacity of C. elegans was also reduced after exposure to 0.1 µM (41.4 µg/L) PFOA. Similarly, developmental toxicity was also documented with the reduction in lifespan and alteration in chemotaxis plasticity above 1 µM (414 µg/L) PFOA. C. elegans bioaccumulated PFOA about 520 times than the surrounding concentration when exposed to 0.41 ug/L PFOA. Given that PFOA has demonstrated its toxicological impacts on the reproductive capacity and lifespan of C. elegans at the concentrations that are commonly found at contaminated areas, it is likely that the contamination of PFOA will have detrimental effects on the food chain in both terrestrial and aquatic ecosystems. Thus, the results of this study have significant implications for the ecological risk assessment and remediation of PFOA.

Pesticides are becoming a significant transnational pollutant in agricultural production environments. This review presents the interconnectedness and interaction effects of pesticides with the microbiomes in the environments of plant rhizosphere and animal (limited to insect and human) guts. The metabolic growth and functions of rhizosphere microbiomes are altered by complex mechanisms involving redox reactions and preferential substrate utilization. The rhizospheres of crop plants with the assemblies of microbiota and other biotic components are sensitive to the deliberate introduction of pesticides. Pesticides become one of the major drivers for the metabolic processes, which rely on the evolutionary mechanisms, including the genetic exchange events within the rhizosphere microbiomes. Pesticides, even at the below detection levels, in the rhizosphere enable the plant uptake which can be up to 1% of the dose applied and trophic transfers involving the animal gut environments. To overcome the metabolic constraints due to the nutrient-poor plant diets contaminated with pesticides, insects gain the resistance traits, mainly due to the pesticide-degrading members of the gut microbiomes. Such evolved microbiome members and their genes can increase their spread of resistance in the environment. Like the insect gut microbiomes, the human gut microbiomes get modulated by the pesticide-laden plant foods, leading to dysbiosis. The confounding effects of pesticides on the gut microbiomes which include mutational and genetic exchange events can upsurge many health disorders. The evolutionary and microbiome perspectives on the rhizosphere and animal guts as the hotspots of metabolic and horizontal gene transfer (HGT) events need careful considerations to mitigate the risks and health hazards due to extensive and intensive application of synthetic chemical pesticides in the modern agriculture.

As an emerging contaminant, microplastic is receiving increasing attention. However, the contamination source is not fully known, and new sources are still being identified. Herewith, we report that microplastics can be found in our gardens, either due to the wrongdoing of leaving plastic bubble wraps to be mixed with mulches or due to the use of plastic landscape fabrics in the mulch bed. In the beginning, they were of large sizes, such as > 5¿mm. However, after 7 years in the garden, owing to natural degradation, weathering, or abrasion, microplastics are released. We categorize the plastic fragments into different groups, 5¿mm¿0.75¿mm, 0.75¿mm¿100¿µm, and 100¿0.8¿µm, using filters such as kitchenware, meaning we can collect microplastics in our gardens by ourselves. We then characterized the plastics using Raman image mapping and a logic-based algorithm to increase the signal-to-noise ratio and the image certainty. This is because the signal-to-noise ratio from a single Raman spectrum, or even from an individual peak, is significantly less than that from a spectrum matrix of Raman mapping (such as 1 vs. 50 × 50) that contains 2,500 spectra, from the statistical point of view. From the 10¿g soil we sampled, we could detect the microplastics, including large (5¿mm¿100¿µm) fragments and small (<100¿µm) ones, suggesting the degradation fate of plastics in the gardens. Overall, these results warn us that we must be careful when we do gardening, including selection of plastic items for gardens.

Physiological changes that drive the microalgal-bacterial consortia are poorly understood so far. In the present novel study, we initially assessed five morphologically distinct microalgae for their ability in establishing consortia in Bold's basal medium with a bacterial strain, Variovorax paradoxus IS1, all isolated from wastewaters. Tetradesmus obliquus IS2 and Coelastrella sp. IS3 were further selected for gaining insights into physiological changes, including those of metabolomes in consortia involving V. paradoxus IS1. The distinct parameters investigated were pigments (chlorophyll a, b, and carotenoids), reactive oxygen species (ROS), lipids and metabolites that are implicated in major metabolic pathways. There was a significant increase (>1.2-fold) in pigments, viz., chlorophyll a, b and carotenoids, decrease in ROS and an enhanced lipid yield (>2-fold) in consortia than in individual cultures. In addition, the differential regulation of cellular metabolites such as sugars, amino acids, organic acids and phytohormones was distinct among the two microalgal-bacterial consortia. Our results thus indicate that the selected microalgal strains, T. obliquus IS2 and Coelastrella sp. IS3, developed efficient consortia with V. paradoxus IS1 by effecting the required physiological changes, including metabolomics. Such microalgal-bacterial consortia could largely be used in wastewater treatment and for production of value-added metabolites.

Bioavailable content of metals in aquatic systems has become critical in assessing the toxic effect of metals accumulating in the environment. Considering the need for rapid measurements, an optical microalgal-cyanobacterial array biosensor was developed using two strains of microalgae, Mesotaenium sp. and a strain of cyanobacteria Synechococcus sp. to detect Cd2þ, Cr6þ and Zn2þ in aquatic systems. Microalgal and cyanobacterial cells were immobilized in a 96-well microplate using sol-gel method using silica. Optimum operational conditions for the biosensor array such as exposure time, storage stability, pH, and multiple metal effect were tested. A 10 min exposure time yielded optimum fluorescence values. Metal toxicity increased with decreasing pH, resulting in low relative fluorescence (%) and decreased with increasing pH, resulting in higher relative fluorescence (%). The optimum storage time for biosensor strains were 4 weeks for microalgal cultures and 8 weeks for cyanobacterial culture, at 4 °C storage temperature. The metal mixtures showed less effect on the inhibition of relative fluorescence (%) of microalgal/cyanobacterial cultures, displaying an antagonistic behavior among the metals tested. As a single unit, this photosynthetic array biosensor will be a valuable tool in detecting multi-metals in aquatic systems.

This novel study investigated the behavior and fate of chlorothalonil in terms of kinetics, sorption¿desorption and leaching potential in urban landscape soils using batch experiments. The pseudo-second-order model well described the sorption kinetics of chlorothalonil in urban soils. Consequently, chlorothalonil was partitioned into heterogeneous surfaces of soil following the Freundlich isotherm model. According to PCA, soil organic matter (OM), silt, clay, and oxides of Al and Fe exhibited a significant positive correlation (P < 0.05) with chlorothalonil K d (P < 0.05), while sand content and soil pH showed a negative correlation at P < 0.05. In soils, decreased sorption of chlorothalonil was also due to the presence of undecomposed or partly decomposed OM, whereas increased sorption could be attributed to the combined effect of OM with C = O and C¿H groups, silt, clay, Al and Fe oxides and hydrophobicity of the fungicide. Also, HI, GUS, LIX and K d of four among nine urban soils indicated that chlorothalonil has a great potential for leaching into the groundwater from the soil surface, posing an unintended threat to non-target biota and food safety. Therefore, utmost care must be taken while applying chlorothalonil in urban landscapes, particularly on impervious surfaces, to minimize the impact on the ecosystem.

Perfluorobutane sulfonate (PFBS), due to its increasing use as an alternative to perfluooctane sulfonate (PFOS), is widely detected in humans and the environment, necessitating the evaluation of its potential ecotoxicological risk. We assessed the toxicity and bioaccumulation potential of PFBS in Caenorhabditis elegans, using lethality, locomotion, reproduction, life span, growth, and chemotactic behavior as the effect parameters. In addition, a total of 6 generations of exposed parent animals were monitored for locomotion, brood, and life span behaviors. Life span and brood size were significantly reduced in parent nematodes (P0) following exposure to =0.1 mM PFBS, but these negative effects did not transfer to the progeny. Although there was no remarkable effect on reproduction and life span in parent worms exposed to =0.01 mM PFBS, multigenerational exposure at 0.0005 mM significantly affected the F4 and F5 progeny. Furthermore, 0.01 to 2.0 mM of PFBS substantially retarded the locomotion behavior of P0 worms. At higher concentrations such as 1.0 mM, this negative effect on locomotion was transferred to the next generation (F1) but later recovered from F2 progeny onward. Our findings demonstrate for the first time that chronic exposure to PFBS at higher concentrations can cause behavioral toxicity and could be transferred to the progeny. These findings have significant implications for the environmental risk assessment of PFBS. Environ Toxicol Chem 2021;40:1973¿1982. © 2021 SETAC.

Unresolved complex mixtures (UCMs) of hydrocarbons are the pollutants of serious concern commonly occurring in most of the environments contaminated with petroleum hydrocarbons. UCMs constitute a relatively unidentified group of compounds compared to the well-resolved hydrocarbons that could easily be identified by the modern chromatographic methods. UCMs that accumulate in the environment cause several toxicological effects of ecological significance, and indirectly affect the human health. Despite decades-long efforts to provide adequate information in this area of research, the fate and environmental impacts of UCMs of petroleum hydrocarbons are poorly understood. Techniques for extraction and analysis of UCMs in the environment are very important in their identification and quantification. Also, remediation of toxic UCMs of petroleum hydrocarbons is all the more essential. In fact, UCMs are often neglected in the risk assessments due to lack of proper identification methods and toxicity data. This critical review presents an overview of our current knowledge on the environmental occurrence, sources, separation, and identification methods for UCMs. The ecological toxicity of UCMs toward the biota and the strategies for remediation of the environments contaminated with UCMs have also been discussed in detail.

Phenotypic plasticity or genetic adaptation in an organism provides phenotypic changes when exposed to the extreme environmental conditions. The resultant physiological and metabolic changes greatly enhance the organism's potential for its survival in such harsh environments. In the present novel approach, we tested the hypothesis whether acid-adapted microalgae, initially isolated from non-acidophilic environments, can survive and grow in acid-mine-drainage (AMD) samples. Two acid-adapted microalgal strains, Desmodesmus sp. MAS1 and Heterochlorella sp. MAS3, were tested individually or in combination (co-culture) for phenotypic changes during their growth in samples collected from AMD. The acid-adapted microalgae in AMD exhibited a two-fold increase in growth when compared with those grown at pH 3.5 in BBM up to 48 h and then declined. Furthermore, oxidative stress triggered several alterations such as increased cell size, granularity, and enhanced lipid accumulation in AMD-grown microalgae. Especially, the apparent limitation of phosphate in AMD inhibited the uptake of copper and iron in the cultures. Interestingly, growth of the acid-adapted microalgae in AMD downregulated amino acid metabolic pathways as a survival mechanism. This study demonstrates for the first time that acid-adapted microalgae can survive under extreme environmental conditions as exist in AMD by effecting significant phenotypic changes.

The biosolids management is becoming an increased concern for the wastewater sector in recent times due to production of large volume of biosolids, their higher processing costs and the presence of emerging contaminants. The pyrolysis of biosolids is gaining significant interest in the industry sector as well as research community over the last decade due to its ability to reduce biosolids volume, produce high-value biochar product and minimise the risk associated with contaminants. This paper aims to critically review the literature on biosolids management techniques and their current challenges, biosolids characteristics and its suitability for pyrolysis, pyrolysis product characterisation from different reactor designs and biochar application as a soil amendment, adsorbent and catalyst. The efforts have also been made to critically summarise studies on the process modelling activities and techno-economic assessments including some key pilot-scale demonstrations of recent time. The review concludes that biosolids to biochar can be an effective alternative to biosolids management; however, its commercial viability is limited in the current scenario. In the end, efforts have been made to highlight current challenges including research gaps and future perspectives in improving its commercial viability.

The environmental fate and impact of dimethoate application in the urban environment were assessed in nine selected soils. The pseudo-second-order kinetics model described the kinetics of dimethoate sorption very well in the urban soils exhibiting two distinct phases, an initial partitioning into clay surfaces and soil organic matter, and eventual diffusion into soil micropores. Dimethoate sorption in the urban soils followed the Freundlich model with an R2 value of 0.94-0.99, suggesting a multi-layered sorption on the heterogeneous surfaces. Sorption of dimethoate in the soils was influenced by clay, silt, organic matter, carboxyl and alkyl groups, and Al and Fe oxides. The undecomposed or incompletely decomposed organic matter present in the soils greatly reduced the sorption and enhanced desorption. The calculated lower values for Freundlich constant (KF) indicate the high mobility of dimethoate in the selected soils. Also, the values of groundwater ubiquity score (GUS), leachability index (LIX), hysteresis index (HI), and coefficient of distribution (Kd) for dimethoate in the soils clearly suggest that the insecticide is prone to leaching out significantly from the soil surface to groundwater. Moreover, the surface runoff from impervious places in the urban environment can be considered as a direct source of groundwater contamination, thereby affecting the quality of potable water besides posing a threat to non-target organisms of ecological importance and food safety. Thus, the present novel study suggests that the application of dimethoate in the urban environment having impervious surfaces must be judicious in order to minimize the potential human and ecological health risks.

Food is the major cadmium (Cd)-exposure pathway from agricultural soils to humans and other living entities and must be reduced in an effective way. A plant can select beneficial microbes, like plant-growth-promoting rhizobacteria (PGPR), depending upon the nature of root exudates in the rhizosphere, for its own benefits, such as plant growth promotion as well as protection from metal toxicity. This review intends to seek out information on the rhizo-immobilization of Cd in polluted soils using the PGPR along with plant nutrient fertilizers. This review suggests that the rhizo-immobilization of Cd by a combination of PGPR and nanohybrid-based plant nutrient fertilizers would be a potential and sustainable technology for phytoavailable Cd immobilization in the rhizosphere and plant cellular detoxification, by keeping the plant nutrition flow and green dynamics of plant nutrition and boosting the plant growth and development under Cd stress.

Chromium from tannery waste dump site causes significant environmental pollution affecting surrounding flora and fauna. The primary aims of this study were to survey vegetation, investigate the degree of soil pollution occurring near tannery waste dump site and make a systematic evaluation of soil contamination based on the chromium levels found in plants and earthworms from the impacted areas. This paper presents the pollution load of toxic heavy metals, and especially chromium, in 10 soil samples and 12 species of plants. Soil samples were analysed for heavy metals by using ICP-MS/ICP-OES method. Results indicated that Cr in soils exceeded soil quality guideline limits (SQGL). The total chromium present in the above ground parts of plants ranged from 1.7¿mg¿kg-1 in Casuarina sp.¿to 1007¿mg¿kg-1 in Sonchus asper. The Cr bioaccumulation in Eisenia fetida from tannery waste soil ranged from 5 to 194¿mg¿kg-1. The high enrichment factor of Cr in S. asper and bioaccumulation factor in earthworms indicate that there is a steady increase of toxic chromium risk in this area, which could be correlated with the past dumping activity. Emphasis needs to be put on control measures of pollution and remediation techniques in such areas to achieve an ecologically sustainable industrialisation.

Heavier fraction hydrocarbons (C15-C36) formed in soil after biotic and abiotic weatherings of engine oil are the continuing constraints in the bioremediation strategy, and their bioavailability remains a poorly quantified regulatory factor. In a microcosm study, we used two strains of Pseudomonas, P. putida TPHK-1 and P. aeruginosa TPHK-4, in strategies of bioremediation, viz., natural attenuation, biostimulation and bioaugmentation, for removal of weathered total petroleum hydrocarbons (TPHs) in soil contaminated long-term with high concentrations of engine oil (39,000¿41,000 mg TPHs kg-1 soil). Both the bacterial strains exhibited a great potential in remediating weathered hydrocarbons of engine oil. Addition of inorganic fertilizers (NPK), at recommended levels for bioremediation, resulted in significant inhibition in biostimulation/enhanced natural attenuation as well as bioaugmentation. The data on dehydrogenase activity clearly confirmed those of bioremediation strategies used, indicating that this enzyme assay could serve as an indicator of bioremediation potential of oil-contaminated soil. Extraction of TPHs from engine oil-contaminated soil with hydroxypropyl-ß-cyclodextrin (HPCD), but not 1-butanol, was found reliable in predicting the bioavailability of weathered hydrocarbons. Also, 454 pyrosequencing data were in accordance with those of bioremediation strategies used in the present microcosm study, suggesting the possible use of pyrosequencing in designing approaches for bioremediation.

Sorption and desorption are critical processes to control the mobility and biotoxicity of cadmium (Cd) in soils. It is known that attendant anion species of heavy metals could affect metal adsorption on soils and might further alter their biotoxicity. However, for Cd, the influence of attendant anions on its sorption in soils and subsequent toxicity on soil enzymes are still unknown. In this work, four Cd compounds with different salt anions (SO42-, NO3-, Cl-, and Ac-) were selected to investigate their impact of on the sorption, soil dehydrogenase activity (DHA) and alkaline phosphatase activity (ALP). Thus, a series of simulated Cd pollution batch experiments including measuring adsorption-desorption behavior of Cd on soils and soil enzyme activities were carried out. Results showed that CdSO4 exhibited highest sorption capacity among the tested soils except in Hunan soil. The Cd sorption with NO3- displayed a similar behavior with Cl- on all tested soils. Compared with soil properties, all four kinds of anions on Cd sorption played a more significant role affecting Cd ecological toxicity to soil DHA and ALP. Cd in acetate or nitrate form appears more sensitive towards DHA than sulphate and chloride, while the later pair is more toxic towards ALP than the former. These results have important implications for evaluation of Cd contamination using soil enzyme as bioindicator.

Diesel is an important petroleum product, and a common pollutant in soil caused by leaks and accidental spills. Studies dealing with the ecotoxicity of diesel towards earthworms always relied on growth inhibition endpoint (EC50) values that were determined based on the spiked concentrations (nominal), ignoring the substantial portion of hydrocarbons volatilized from soil. In the present study we used, for the first time, the measured concentrations of total petroleum hydrocarbons (TPHs) from soil-applied diesel to assess earthworm (Eisenia fetida) survival, and the activities of dehydrogenase, urease and nitrification as indicators of soil health. The mortality endpoint (LC50) value for initially measured concentrations after exposure of earthworms to diesel for 28¿days was 916¿±¿10¿mg TPHs kg-1 soil which was equivalent to the nominal (initially added) concentration of 1426¿±¿19¿mg TPHs kg-1 soil. Morphological abnormalities such as clitella swelling and curling were noticed when the measured concentrations of diesel were more than 971¿mg¿kg-1 soil. Significant increases in activities of soil dehydrogenase (38¿58%) as well as urease were observed in the diesel-applied soil. Presence of earthworms further enhanced the activities of these soil enzymes. Nitrification was sensitive to application of diesel to soil, and it was inhibited in a dose-related manner even in the presence of earthworms. The differential response of the toxicity criteria to diesel-contaminated soil observed in the present study clearly warrants more studies involving several soil health parameters to arrive at a generalization of ecotoxicity of an environmental pollutant.

This study investigates the effect of contaminant zinc (Zn) on lead (Pb) bioavailability and bioaccessibility in six contrasting soils spiked with 1500 mg Pb/kg and aged 12 months under laboratory conditions. Zn was added to the soils (7500 mgZn/kg soil) and aged for a further two weeks. In vivo studies were conducted using juvenile swine as a surrogate model for young children. Two compartment pharmacokinetic models were used to analyze the biological response produced by Pb oral solution and spiked soils. Absolute and relative bioavailability of Pb in soils (oral dose of 100 µ g Pb/kg body weight/day) were estimated by comparing them with intravenously administered soluble Pb salt (25 µ g Pb/kg/day) and orally administered the same Pb salt [Pb acetate =(CH3COO)2Pb·3H2O] administered to 3 juvenile pigs per treatment. Lead bioaccessibility was calculated using the in vitro RBALP (i.e. relative bioaccessibility leaching procedure) method. The in vitro results of RBALP were compared to in vivo relative Pb bioavailability to ascertain whether the changes in bioaccessibility correlated with the in vivo data. Although the in vivo Pb relative bioavailability (RB) in all soils except in MLA (Mount Lofty Acidic) revealed an increase (18%¿159%) in the presence of Zn, the in vitro RBALP bioaccessibility results indicated otherwise (1%¿38% decrease). In vivo RB of Pb in MLA declined by 37% in the presence of Zn. However, the RBALP in vitro bioaccessible Pb did not correlate with the relative bioavailabilities of Pb in the juvenile swine dosing experiment. Caution is therefore needed when predicting Pb bioavailability/bioaccessibility in the presence of metal mixtures. The literature contains much information on the correlation of metal and metalloid bioaccessibility with their bioavailability. There is, however, a paucity of studies investigating the effects of other metals on Pb and their IVIVC (in vitro and in vivo correlations). The current study addresses this knowledge gap by assessing in vivoand in vitro bioavailability of Pb in the presence of Zn.

Purpose: The study evaluates and provides an overview of the nutritional importance of 19 selected food wastes as aids in human/livestock/soil/plant health. Methods: Nitric acid-digested extracts of food wastes belonging to four different classes (fruits, vegetables, oilseeds and beverages) were analysed for different elements in an inductively coupled plasma mass spectrometer. Results: Our study recommends spent coffee grounds, tea leaves, radish peel, watermelon rind and pineapple skin that contain substantially high concentrations of essential elements such as N, P, K, S and Fe for their use as: (a) substrates for composting, (b) biofertilizers, (c) soil amendments, and (d) bioadsorbents of toxins. Although these food wastes are rich in essential nutrients, we do not suggest them for the preparation of food supplements as they contain non-essential elements in concentrations beyond the human safety limits. However, food wastes like banana peel, plum pomace and pistachio shell that contain low and permissible concentrations of toxic elements can be recommended as dietary supplements for oral intake in spite of their lesser essential elemental composition than the other residues examined. Conclusions: Our study confirms that food wastes are rich sources of essential nutrients and there is need to harness their real industrial systems.

Arsenic (As) and zinc (Zn) are common co-contaminants in mining impacted soils. Their interaction on solubility and toxicity when present concurrently is not well understood in natural systems. The aim of this study was to observe their interaction in solubility (soil-solution), bioaccumulation (shoot uptake) and toxicity to cucumber (Cucumis sativa L) conducting 4 weeks pot study in 5 different soils spiked with As (0, 2, 4, 8 to 1024 mg kg-1) individually and with Zn at two phytotoxic doses. The As pore-water concentration was significantly reduced (df = 289, Adjusted R2 = 0.84, p < 0.01) in the presence of Zn in the whole dataset, whereas Zn and Zn2+ activity in pore-water was reduced significantly only in the two alkaline soils. This outcome may be due to adsorption/surface precipitation or tertiary bridging complexation. No homogenous precipitation of zinc arsenate could be established using electron microscopy, XRD or even equilibrium calculations. For bioaccumulation phase, no significant effect of Zn on As uptake was observed except acidic MG soil whereas, Zn uptake was significantly reduced (p < 0.05) by As in whole dataset. However, an additive response was observed mostly except acidic MG soil. The synergistic response (more than additive) was predominant in this soil for a wide range of inhibition concentration (0¿80%) at both Zn EC10 and EC50 levels. Since additive response is mostly considered in risk assessment for mixtures, precautions should be implemented for assessment of toxicity for As-Zn mixture in acidic soil due to their synergistic response in some soils.

Bioelectrochemical remediation (BER) systems such as microbial fuel cells (MFCs) have recently emerged as a green technology for the effective remediation of petroleum hydrocarbon contaminants (PH) coupled with simultaneous energy recovery. Recent research has shown that biofilms previously enriched for substrate degrading bacteria resulted in excellent performance in terms of substrate removal and electricity generation but the effects on hydrocarbon contaminant degradation were not examined. Here we investigate the differences between enriched biofilm anodes and freshly inoculated new anodes in diesel fed single chamber mediatorless microbial fuel cells (DMFC) using various techniques for the enhancement of PH contaminant remediation with concomitant electricity generation. An anodophilic microbial consortium previously selected for over a year through continuous culturing with a diesel concentration of about 800mgl^-1 and which now showed complete removal of this concentration of diesel within 30days was compared to that of a freshly inoculated new anode MFC (showing 83.4% removal of diesel) with a simultaneous power generation of 90.81mW/m² and 15.04mW/m² respectively. The behaviour of pre-cultured anodes at a higher concentration of PH (8000mgl^-1) was also investigated. Scanning electron microscopy observation revealed a thick biofilm covering the pre-cultured anodic electrode but not the anode from the freshly inoculated MFC. High resolution imaging showed the presence of thin 60nm diametre pilus-like projections emanating from the cells. Anodic microbial community profiling confirmed that the selection for diesel degrading exoelectrogenic bacteria had occurred. Identification of a biodegradative gene (alkB) provided strong evidence of the catabolic pathway used for diesel degradation in the DMFCs.

Microalgae are extensively used in the remediation of heavy metals like iron. However, factors like toxicity, bioavailability and iron speciation play a major role in its removal by microalgae. Thus, in this study, toxicity of three different iron salts (FeSO4, FeCl3 and Fe(NO3)3) was evaluated towards three soil microalgal isolates, Chlorella sp. MM3, Chlamydomonas sp. MM7 and Chlorococcum sp. MM11. Interestingly, all the three iron salts gave different EC50 concentrations; however, ferric nitrate was found to be significantly more toxic followed by ferrous sulphate and ferric chloride. The EC50 analysis revealed that Chlorella sp. was significantly resistant to iron compared to other microalgae. However, almost 900¿µg¿g-1 iron was accumulated by Chlamydomonas sp. grown with 12¿mg¿L-1 ferric nitrate as an iron source when compared to other algae and iron salts. The time-course bioaccumulation confirmed that all the three microalgae adsorb the ferric salts such as ferric nitrate and ferric chloride more rapidly than ferrous salt, whereas intracellular accumulation was found to be rapid for ferrous salts. However, the amount of iron accumulated or adsorbed by algae, irrespective of species, from ferrous sulphate medium is comparatively lower than ferric chloride and ferric nitrate medium. The Fourier transform infrared spectroscopy (FTIR) analysis shows that the oxygen atom and P = O group of polysaccharides present in the cell wall of algae played a major role in the bioaccumulation of iron ions by algae.

The efficiency of low-cost, abundantly available local forestry waste, oak (Quercus robur) acorn peel (OP), to remove toxic Cr(VI) from aqueous solutions was studied in a batch system as a function of contact time, adsorbate concentration, adsorbent dosage, and pH. In an equilibrium time of 420 min, the maximum Cr removal by OP at pH 2 and 10 was 100 and 97 %, respectively. The sorption data fitted well with Langmuir adsorption model. Evaluation using Langmuir expression presented a monolayer sorption capacity of 47.39 mg g-1 with an equilibrium sorbent dose of 5 g L-1 and pH 7. Uptake of Cr by OP was described by pseudo-second-order chemisorption model. ICP-OES, LC-ICPMS analysis of the aqueous and solid phases revealed that the mechanism of Cr(VI) removal is by 'integrated adsorption and reduction' mechanism. ESEM-EDX and XRD analysis of OP before and after adsorption also confirmed that both adsorption and reduction of Cr(VI) to less toxic Cr3+ forms followed by complexation onto the adsorbent surface contributed to the removal of Cr(VI). Consistent with batch studies, OP effectively removed (>95 %) Cr from the real water samples collected from lake and sea. The results of this study illustrate that OP could be an economical, green, and effective biomaterial for Cr(VI) removal from natural aquatic ecosystems and industrial effluents.

A mercury resistant bacterial strain, SA2, was isolated from soil contaminated with mercury. The 16S rRNA gene sequence of this isolate showed 99% sequence similarity to the genera Sphingobium and Sphingomonas of a-proteobacteria group. However, the isolate formed a distinct phyletic line with the genus Sphingobium suggesting the strain belongs to Sphingobium sp. Toxicity studies indicated resistance to high levels of mercury with estimated EC50 values 4.5 mg L-1 and 44.15 mg L-1 and MIC values 5.1 mg L-1 and 48.48 mg L-1 in minimal and rich media, respectively. The strain SA2 was able to volatilize mercury by producing mercuric reductase enzyme which makes it potential candidate for remediating mercury. ICP-QQQ-MS analysis of Hg supplemented culture solutions confirmed that almost 79% mercury in the culture suspension was volatilized in 6 h. A very small amount of mercury was observed to accumulate in cell pellets which was also evident according to ESEM-EDX analysis. The mercuric reductase gene merA was amplified and sequenced. The deduced amino acid sequence demonstrated sequence homology with a-proteobacteria and Ascomycota group.

Diversity, distribution and composition of bacterial community of soils contaminated long-term with both polycyclic aromatic hydrocarbons (PAHs) and heavy metals were explored for the first time following 454 pyrosequencing. Strikingly, the complete picture of the Gram positive (+ve) and Gram negative (-ve) bacterial profile obtained in our study illustrates novel postulates that include: (1) Metal-tolerant and PAH-degrading Gram -ves belonging to the class Alphaproteobacteria persist relatively more in the real contaminated sites compared to Gram +ves, (2) Gram +ves are not always resistant to heavy metal toxicity, (3) Stenotrophomonas followed by Burkholderia and Pseudomonas are the dominant genera of PAH degraders with high metabolic activity in long-term contaminated soils, (4) Actinobacteria is the predominant group among the Gram +ves in soils contaminated with high molecular weight PAHs that co-exist with toxic heavy metals like Pb, Cu and Zn, (5) Microbial communities are nutrient-driven in natural environments and (6) Catabolically potential Gram +/-ves with diverse applicability to remediate the real contaminated sites evolve eventually in the historically-polluted soils. Thus, the most promising indigenous Gram +/-ve strains from the long-term contaminated sites with increased catabolic potential, enzymatic activity and metal tolerance need to be harnessed for mixed contaminant cleanups.

Eisenia fetida is a terrestrial organism, which can be used to diagnose sub-lethal concentrations of PFOA by using molecular biomarkers. In order to identify potential molecular biomarkers, we have exposed E.¿fetida to 10¿mg/kg of PFOA in soil for 8¿months. The mRNA isolation, sequencing, transcriptome assembly followed by differential gene expression studies have revealed that genes that are involved in apoptotic process, reproduction, calcium signalling, neuronal development and lipid metabolism are predominantly affected. Highly specific genes that are altered by PFOA can be further validated and used as biomarker to detect sub-lethal concentrations of PFOA in the soil.

Since crude oil contamination is one of the biggest environmental concerns, its removal from contaminated sites is of interest for both researchers and industries. In situ bioremediation is a promising technique for decreasing or even eliminating crude oil and hydrocarbon contamination. However, since these compounds are potentially toxic for many microorganisms, high loads of contamination can inhibit the microbial community and therefore reduce the removal rate. Therefore, any strategy with the ability to increase the microbial population in such circumstances can be of promise in improving the remediation process. In this study, multiwall carbon nanotubes were employed to support microbial growth in sediments contaminated with crude oil. Following spiking of fresh water sediments with different concentrations of crude oil alone and in a mixture with carbon nanotubes for 30. days, the microbial profiles in these sediments were obtained using FLX-pyrosequencing. Next, the ratios of each member of the microbial population in these sediments were compared with those values in the untreated control sediment. This study showed that combination of crude oil and carbon nanotubes can increase the diversity of the total microbial population. Furthermore, these treatments could increase the ratios of several microorganisms that are known to be effective in the degradation of hydrocarbons.

In this study, the influence of soil types on the effect of the commercial form of C-nZVI on tissue concentrations, cellular component, reproduction outcome in Eisenia fetida, and the soil health was investigated. C-nZVI at concentration level of 3¿g¿kg-1 soil showed no effect on the survival of E. fetida in the three soil types. However, varying effects such as concentration-dependent increase in tissue iron concentration, lipid peroxidation, and damage to DNA molecules by C-nZVI were observed. C-nZVI at an exposure concentration of 60¿mg¿kg-1 soil induced oxidative stress in E. fetida. Tissue Fe concentration appeared correlated to the DNA damage. Oxidative stress and DNA damage may explain the toxicity mechanisms of nZVI to E. fetida. [Figure not available: see fulltext.].

© 2016, © Taylor & Francis Group, LLC.Systematic site survey for sample collection and analysis was conducted at a derelict copper (Cu) mine at Kapunda, South Australia. Cu concentrations in the soils at this former mine ranged from 65¿10107¿mg kg-1. The pH and EC varied widely in the 3.9¿8.4 and 152¿7311¿µS ranges, respectively. Nine plant species growing over the copper mine site were selected to screen for metal uptake to determine their suitability for phytoremediation. The Australian native tree species Eucalyptus camaldulensis indicated enrichment factor (EF) of 2.17, 1.89, and 1.30 for Cu, Zn, and Pb, respectively, suggesting that this species of tree can accumulate these metals to some degree. The stress-resistant exotic olive, Olea europaea exhibited EF of = 0.01 for Cu, Cd, and Pb, and 0.29 for Zn, which is characteristic of an excluder plant. Acacia pycnantha, the Australian pioneer legume species with EF 0.03, 0.80, 0.32, and 0.01 for Cu, Zn, Cd, and Pb, respectively, emerged as another strong metal excluder and consequently as an ideal metal stabilizer.

© 2016 American Institute of Chemical Engineers Soils contaminated with crude oil are rich sources of enzymes suitable for both degradation of hydrocarbons through bioremediation processes and improvement of crude oil during its refining steps. Due to the long term selection, crude oil fields are unique environments for the identificati on of microorganisms with the ability to produce these enzymes. In this metagenomic study, based on Hiseq Illumina sequencing of samples obtained from a crude oil field and analysis of data on MG-RAST, Actinomycetales (9.8%) were found to be the dominant microorganisms, followed by Rhizobiales (3.3%). Furthermore, several functional genes were found in this study, mostly belong to Actinobacteria (12.35%), which have a role in the metabolism of aliphatic and aromatic hydrocarbons (2.51%), desulfurization (0.03%), element shortage (5.6%), and resistance to heavy metals (1.1%). This information will be useful for assisting in the application of microorganisms in the removal of hydrocarbon contamination and/or for improving the quality of crude oil. © 2016 American Institute of Chemical Engineers Biotechnol. Prog., 32:638¿648, 2016.

The development of highly efficient, eco-friendly and cost-effective remediation technology to remove mixed contaminants is now in progress. Here, agarose-Fe nanoparticles (NPs) hydrogel were produced via two green steps to remove mixed contaminants, specifically trichloroethylene (TCE) and hexavalent chromium (Cr(VI)). Approx. 84.9% of Cr(VI) and 93.8% of TCE were simultaneously removed over 24 h in their co-existing solution, while 94.1% of Cr(VI) and 97.2% of TCE were separately removed by agarose-Fe NPs hydrogel. Scanning Electron Microscopy (SEM) suggested that the macroporosity of agarose-Fe NPs hydrogel facilitated the mass transfer between agarose-Fe NPs hydrogels and mixed contaminants, and that Fe NPs were uniformly immobilized into the hydrogel. X-ray Photoelectron Spectroscopy (XPS) and Fourier Transform Infrared Spectroscopy (FTIR) provided evidence supporting the co-removal mechanism. XPS result indicated that: (1) chemical reduction played a role in the removal of both Cr(VI) and TCE; and (2) iron oxides and Fe(III)-Cr(III) complexes might be formed after reaction. FTIR result showed that some functional groups were involved in the removal process. Moreover, the presence of iron oxides were confirmed by FTIR. Both SEM and XPS results verified that encapsulation could describe such immobilization of Fe NPs using agarose. Finally, the kinetics study supported the removal mechanism. Such encapsulation of Fe NPs via a green strategy is simple, quick, and cost-effective, making in situ remediation of mixed contaminants more favorable.

The lack of awareness for timely management of the environment surrounding a metal mine site results in several adverse consequences such as rampant business losses, abandoning the bread-earning mining industry, domestic instability and rise in ghost towns, increased environmental pollution, and indirect long-term impacts on the ecosystem. Although several abandoned mine lands (AMLs) exist globally, information on these derelict mines has not been consolidated in the literature. We present here the state-of-the-art on AMLs in major mining countries with emphasis on their impact towards soil health and biodiversity, remediation methods, and laws governing management of mined sites. While reclamation of metalliferous mines by phytoremediation is still a suitable option, there exist several limitations for its implementation. However, many issues of phytoremediation at the derelict mines can be resolved following phytostabilization, a technology that is effective also at the modern operational mine sites. The use of transgenic plant species in phytoremediation of metals in contaminated sites is also gaining momentum. In any case, monitoring and efficacy testing for bioremediation of mined sites is essential. The approaches for reclamation of metalliferous mines such as environmental awareness, effective planning and assessment of pre- and post-mining activities, implementation of regulations, and a safe and good use of phytostabilizers among the native plants for revegetation and ecological restoration are discussed in detail in the present review. We also suggest the use of microbially-enhanced phytoremediation and nanotechnology for efficient reclamation of AMLs, and identify future work warranted in this area of research. Further, we believe that the integration of science of remediation with mining policies and regulations is a reliable option which when executed can virtually balance economic development and environmental destruction for safer future.

An arsenic hyper-tolerant diazotrophic bacterium was isolated from a heavy metal contaminated soil. The pure isolate MM-17 was identified as Azospirillum sp. based on phylogenetic analysis of 16S rRNA. The strain oxidized 100 µM As(III) to As(V) in both culture media (minimal salts) and real groundwater within 8 and 10 h, respectively. The oxidation of As(III) by this strain was observed within the pH range 5-10 with the best performance at pH 7-8. As(III) oxidation was found to be independent of cell growth which implies the oxidation enzymes are constitutively expressed. The whole cell kinetic study highlighted a lower value of kinetic constant, Ks as 32.9 µM As(III), which indicates that the strain MM-17 has greater affinity for As(III). The gene sequence of the large subunit of arsenite oxidase of MM-17 showed 99 and 72% similarity to the large subunit of arsenite oxidase of Stenotrophomonas sp. MM-7 and Sinorhizobium sp. M14, respectively. Sphaeroplasts experiments suggest that arsenite oxidase is a membrane associated protein in MM-17.

Treatability studies in real contaminated soils are essential to predict the feasibility of microbial consortium augmentation for field-scale bioremediation of contaminated sites. In this study, the biodegradation of a mixture of seven PAHs in a manufactured gas plant (MGP) soil contaminated with 3967 mg kg-1 of total PAHs using novel acid-, metal-tolerant, N-fixing, P-solubilizing, and biosurfactant-producing LMW and HMW PAH-degrading bacterial combinations as inoculums was compared in slurry- and solid-phase microcosms over natural attenuation. Bioaugmentation of 5 % of bacterial consortia A and N in slurry- and solid-phase systems enhanced 4.6-5.7 and 9.3-10.7 % of total PAH degradation, respectively, over natural attenuation. Occurrence of 62.7-88 % of PAH biodegradation during natural attenuation in soil and slurry illustrated the accelerated rate of intrinsic metabolic activity of the autochthonous microbial community in the selected MGP soil. Monitoring of the total microbial activity and population of PAH degraders revealed that the observed biodegradation trend in MGP soil resulted from microbial mineralization. In the slurry, higher biodegradation rate constant (k) and lower half-life values (t 1/2) was observed during bioaugmentation with consortium N, highlighting the use of bioaugmentation in bioslurries/bioreactor to achieve rapid and efficient bioremediation compared to that of a static solid system. In general, natural attenuation was on par with bioaugmentation. Hence, depending on the type of soil, natural attenuation might outweigh bioaugmentation and a careful investigation using laboratory treatability studies are highly recommended before the upscale of a developed bioremediation strategy to field level.

To reduce cost and enhance reactivity, bimetallic Fe/Pd nanoparticles (NPs) were firstly synthesized using grape leaf aqueous extract to remove Orange II. Green synthesized bimetallic Fe/Pd NPs (98.0%) demonstrated a far higher ability to remove Orange II in 12h compared to Fe NPs (16.0%). Meanwhile, all precursors, e.g., grape leaf extract, Fe2+ and Pd2+, had no obvious effect on removing Orange II since less than 2.0% was removed. Kinetics study revealed that the removal rate fitted well to the pseudo-first-order reduction and pseudo-second-order adsorption model, meaning that removing Orange II via Fe/Pd NPs involved both adsorption and catalytic reduction. The remarkable stability of Fe/Pd NPs showed the potential application for removing azo dyes. Furthermore, Scanning Electron Microscopy (SEM) and Fourier Transform Infrared Spectroscopy (FTIR) confirmed the changes in Fe/Pd NPs before and after reaction with Orange II. High Performance Liquid Chromatography-Mass Spectrum (HPLC-MS) identified the degraded products in the removal of Orange II, and finally a removal mechanism was proposed. This one-step strategy using grape leaf aqueous extract to synthesize Fe/Pd NPs is simple, cost-effective and environmentally benign, making possible the large-scale production of Fe/Pd NPs for field remediation.

We demonstrated SERS (surface-enhanced Raman scattering) detection of fluorosurfactants (FSs), which are commonly formulated in aqueous firefighting foams (AFFFs), by increasing their loading affinity and boosting their Raman activity. In order to increase FS's loading affinity, we introduced a cationic dye (ethyl violet or methyl blue) into the aqueous incubation solution to co-precipitate the FS onto the SERS substrate surface by forming an immiscible ion-pair (dye-FS). In the meantime, the Raman signal intensity was boosted due to the much higher Raman activity of the dye than that of FS. We compared two kinds of SERS substrate, patterned silver (Ag) surface and graphene oxide (GO) membrane, and noted the former (dye-FS-Ag) enhanced the Raman signal whilst the latter (dye-FS-GO) increased the loading affinity of the ion-pair due to the hydrophobic surface. We thus introduced silver nanoparticles (AgNPs) into the incubation solution (as well as dye) to co-precipitate FS onto the GO surface via an assembly of dye-FS-AgNP-GO. Using this assembly, we successfully detected FSs including pentadecafluorooctanoic acid (PFOA), perfluorooctanesulfonic acid (PFOS), and 1H,1H,2H,2H-perfluorooctanesulfonic acid (6:2FTS), with a limit-of-detection (LOD) of ~50 ppb (~120 nM) for PFOA.

We exposed the microalgal strain, Chlorella sp. MM3, to unused or used engine oil, or their water accommodated fractions (WAFs) to determine growth inhibition and response of antioxidant enzymes. Oil type and oil concentration greatly affected the microalgal growth. Used oil at 0.04¿% (0.4¿g L-1) resulted in 50¿% inhibition in algal growth, measured in terms of chlorophyll-a, while the corresponding concentration of unused oil was nontoxic. Similarly, used oil WAF showed significant toxicity to the algal growth at 10¿% level, whereas WAF from unused oil was nontoxic even at 100¿% concentration. Peroxidase enzyme in the microalga significantly increased with used oil at concentrations above 0.04¿g L-1 whereas the induction of superoxide dismutase and catalase was apparent only at 0.06¿g L-1. Activities of the antioxidant enzymes increased significantly when the microalga was exposed to 75 and 100¿% WAF obtained from used oil. The used oil toxicity on microalga could be due to the presence of toxic soluble mono- and polyaromatic compounds, heavy metals, and other compounds attained by the oil during its use in the motor engines.

Worldwide a multitude of firefighting compounds are currently used for the mitigation and protection of man-made structures and forests alike from fire damages. Among the class of firefighting agents, Class B firefighting foams are generally used to control fires generated from hydrocarbon liquids. In the present study, we assessed the cyto- and genotoxicity of two widely used class B firefighting foam concentrates, Tridol-S 3% and Tridol-S 6% to Alliumcepa through chromosomal aberration and comet assay using root meristem cells. A. cepa root tips were exposed to Tridol-S 3% and Tridol-S 6% with six different concentrations (0%, 0.005%, 0.01%, 0.02%, 0.03%, 0.04% and 0.05%) for 24 h. Cytogenetic effect endpoints such as mitotic index, and chromosomal aberrations were observed. Chromosomal aberrations in the control (untreated onion root tips) was negligible with the mitotic index (MI) value of 79.6%, while the MI significantly decreased in all the test concentrations of firefighting compounds. Genotoxicity assessment through comet assay also revealed that both the products were genotoxic with a significant increase in per cent tail DNA and olive tail moment. Among the test compounds, Tridol-S 3% was more toxic than Tridol-S 6%. To our knowledge, this is the first study on the cyto- and genotoxic effects of class B firefighting foams to A. cepa root meristem cells. This study also suggests that the toxicological studies using A. cepa root meristem cells can be employed for evaluating the toxicological impacts of firefighting foams in the environment.

A mercury resistant bacterial strain SE1 isolated from contaminated soil was identified as Pseudoxanthomonas based on 16s rRNA sequencing. The Hg resistance was examined in both nutrient-rich media as well as low nutrient media and expressed as EC50 and MIC values. Estimated EC50 and MIC values in nutrient-rich media and low nutrient media had the following respective recordings ¿ 22.6 mg L-1; 23.1 mg L-1 and 1.4 mg L-1 and 1.7 mg L-1. The isolate was able to volatilize inorganic mercury demonstrated by a modified photographic film experiment and subsequently revealed its ability to remove mercury from the solution. The ICP-QQQ-MS analysis of SE1 inoculated solution showed almost 60% of 1.5 mg L-1 mercury was volatilized in 6 h and almost 40% were accumulated in cell pellets. The mercuric reductase gene merA was identified in the genome of isolate SE1 and sequenced. The deduced amino acid sequence of merA gene indicated a sequence homology with different organisms from the alpha proteobacteria group and eukaryotic fungi. merA encoded enzyme mercuric reductase activity was evident in the crude protein of the isolate. The isolate's ability to resist Hg, it's Hg volatilization potential and the presence of merA gene and mercuric reductase enzyme demonstrates the potential application of this strain in mercury bioremediation.

Dearth of high molecular weight contaminant degradation, pH tolerance and growth limiting nutrient assimilation potentials of the selected microorganisms are some of the prime factors reasonable for the failures in field-scale bioremediation of PAHs contaminated soils. Hence an effort was made in this study for the first time to identify HMW PAHs degrading, N-fixing and P-solubilizing bacteria with pH tolerance from long-term manufactured gas plant site soils. Four distinct strains that could degrade both LMW and HMW PAHs were identified. Among the isolates, Stenotrophomonas (MTS-2) followed by Citrobacter (MTS-3) and Pseudomonas (MTS-1) were furthermost effective in the degradation of HMW PAHs either as individual or in the presence of co-substrate (LMW PAHs). MTS-1, 2 and 3 (co)degraded model LMW PAHs, Phe (100% of 150 mg L-1) and HMW PAHs Pyr (100% of 150 mg L-1) or BaP (90¿100% of 50 mg L-1) in 3, 12¿15 and 30 days, respectively and recorded the least half-life time (t1/2) and highest biodegradation rate constants (k). One of the significant findings is the diazotrophic P-solubilization ability, acid and alkali tolerance (optimum pH=5.0¿8.0) of the HMW PAHs degrading Pseudomonas strain MTS-1. Stenotrophomonas (MTS-2) was also found to be superior as it could solubilize P and tolerate acidic condition (optimum pH=5.0¿7.5) during HMW PAHs degradation. Further, our study is the first evidence of diazotrophic P solubilization potential of Agrobacterium (MTS-4) and P-solubilizing capacity of Citrobacter (MTS-3) during bioremediation. Thus, the results of this study demonstrate the promising use of the newly identified PAH degraders, notably MTS-1, 2 and 3 either as individuals or as consortia as an excellent candidate in the bioremediation or phytoremediation of PAHs contaminated soils.

A new green microalgal species was isolated, identified and investigated for its biomass production and nutrient removal efficiency in dairy and winery wastewater in this study. The 18S rRNA-based phylogenetic analysis revealed that this new strain is a Diplosphaera sp. and was designated strain MM1. The growth of this strain was evaluated in different diluted dairy and winery wastewaters. The highest algal biomass production (up to 2.3¿g¿L-1) was obtained in dairy wastewater (D3; dairy wastewater 1:2 deionised water) after 14¿days of culture. However, for winery wastewater, the highest algal biomass production (up to 1.46¿g¿L-1) was obtained in wastewater combination W2 (winery wastewater 1:1 deionised water) after 14¿days of culture. Turbid dairy wastewater with high concentration of nitrogen and phosphorous slowed down the initial growth of the alga. However, at the end of day 14, biomass production was nearly twofold higher than that of winery wastewater. The findings from both types of wastewater suggest that Diplosphaera sp. MM1 has potential for its application in generating biomass with simultaneous remediation of nutrient-rich wastewater.

The presence of sulphur-substituted hydrocarbons in fossil fuels are one of main reasons for the release of sulfur oxides into the environment. Dibenzothiophenes (DBT) are organic sulfur-containing molecules in crude oil, which have the potential for biological oxidation, with the sulphur being removed through an enzymatic cleavage of the C. S bonds. Therefore, finding new strains that can desulfurize this compound has recently become a point of interest. In this study, three new genes involved in the bacterial desulfurization of Dibenzothiophene, which were sequenced in the course of a metagenomic study, were isolated by PCR amplification in the laboratory. The activities of these genes were then analysed following insertion into an expression vector and cloning in Escherichia coli DH5a cells. Based on the results, all three genes were actively expressed and their products could act on their corresponding substrates.

The present study describes for the first time the utilization of dried twigs of Melaleuca diosmifolia, fallen off from the plant, to detoxify and remove hexavalent chromium or Cr(VI) from aqueous systems. Initial characterization by gas chromatography revealed that the selected biomaterial is one of the natural sources of eucalyptol. It constituted high concentrations of reducing compounds (iron, phenols and flavonoids). Batch studies revealed that the biosorbent (5 g L-1) was able to remove 97-99.9% of 250 mg L-1 Cr(VI) at wide-ranging pH (2-10) and temperature (24-48 °C). Adsorption kinetics was well described using the pseudo-second-order kinetic model, while the equilibrium adsorption data were interpreted in terms of the Langmuir isotherm model. The monolayer adsorption capacity was 62.5 mg g-1. Both inductively coupled plasma optical emission spectrometry and liquid chromatography analyses of the aqueous and solid phases revealed that the mechanism of Cr(VI) removal was 'adsorption-coupled reduction'. Scanning electron microscope, infrared spectroscopy and X-ray diffraction analyses of the biosorbent before and after adsorption also confirmed that both adsorption and reduction of Cr(VI) to Cr(III) followed by complexation onto functional groups of the active surface contributed to the removal of Cr(VI) from aqueous solution. The selected biomaterial effectively (99.9%) removed Cr(VI) in lake and sea water samples, highlighting its potential for remediating Cr(VI) in real environmental conditions.

Barite contamination of soil commonly occurs from either barite mining or explorative drilling operations. This work reported in vitro data for barite contaminated soils using the physiologically based extraction test (PBET) methodology. The existence of barite in plant tissue and the possibility of 'biomineralised' zones was also investigated using Scanning Electron Microscopy. Soils with low barium (Ba) concentrations showed a higher proportion of Ba extractability than barite rich samples. Barium uptake to spinach from soil was different between short term spiking studies and field weathered soils. Furthermore, Ba crystals were not evident in spinach tissue or acid digest solutions grown in barium nitrate spiked soils despite high accumulation. Barite was found in the plant digest solutions from barite contaminated soils only. Results indicate that under the conservative assumptions made, a child would need to consume extreme quantities of soil over an extended period to cause chronic health problems.

Recent decades have seen a growing popularity of in vitro bioaccessibility being utilised as a screening tool in human health risk assessment. However the existing bioaccessibility studies only focus on single contaminant. Considering human are likely to ingest multi-contaminants, these contaminants could interact within human gastrointestinal tract which may lead to an increase or decrease in bioaccessibility. In this study, seven different types of soil were spiked with arsenic (As) or cadmium (Cd) and aged for one year. The effects of soil properties on the bioaccessibility were examined. Moreover, the interaction between As and Cd in simulated human digestive system was studied by mixing As-spiked soil with Cd-spiked soil of the same type during bioaccessibility test. Results shows the bioaccessibility of As ranged from 40 ± 2.8 to 95 ± 1.3% in the gastric phase and 16 ± 2.0 to 96 ± 0.8% in the intestinal phase whilst a significant difference was observed between Cd gastric bioaccessibility (72 ± 4.3 to 99 ± 0.8%) and intestinal bioaccessibility (6.2 ± 0.3 to 45 ± 2.7%). Organic carbon, iron oxide and aluminium oxide were key parameters influencing the bioaccessibility of As (gastric and intestinal phases) and Cd (intestinal phase). No interactions between As and Cd during bioaccessibility test were observed in any soils, which indicates As and Cd may age independently and did not interact while being solubilised during bioaccessibility test. Thus additive effect may be proposed when estimating the bioaccessibility of mixtures of independently-aged As and Cd in soils.

Four bacterial strains, capable of degrading diesel oil, n-alkanes or hexadecane, were isolated from soils contaminated with petroleum oil and identified. Strains of Pseudomonas sp., Pseudomonas putida TPHK-1 and Pseudomonas aeruginosa TPHK-4, were more efficient in degrading high concentrations of the hydrocarbons than the other two strains, Stenotrophomonas maltophilia TPHK-2 and Acenitobacter sp. TPHK-3. P. putida TPHK-1 exhibited tolerance to very high concentrations of heavy metals such as cadmium, lead, zinc and copper. The innate ability of P. putida TPHK-1, as evidenced by the amplified genes alkB1 and alkB2 that encode alkane hydroxylases, and cat12o and cat23o coding for catechol dioxygenase, in degrading diesel oil in the presence of heavy metals is far greater than that of the strains reported in the literature. Heavy metal tolerance coupled with rapid degradation of hydrocarbons, even at high concentrations, suggests that P. putida TPHK-1 has a great potential in remediating soils contaminated with mixtures of hydrocarbons and heavy metals.

An isolate of Cupriavidus (strain MTS-7) was identified from a long-term PAHs and heavy metals mixed contaminated soil with the potential to biodegrade both LMW and HMW PAHs with added unique traits of acid and alkali tolerance, heavy metal tolerance, self-nutrient assimilation by N fixation and P solubilization. This strain completely degraded the model 3 (150¿mg¿L-1 Phe), 4 (150¿mg¿L-1 Pyr) and 5 (50¿mg¿L-1 BaP) ring PAHs in 4, 20 and 30 days, respectively. It could mineralize 90¿100% of PAHs (200¿mg¿L-1 of Phe and Pyr) within 15 days across pH ranging from 5 to 8 and even in the presence of toxic metal contaminations. During biodegradation, the minimum inhibitory concentrations were 5 (Cu2+) and 3 (Cd2+, Pb2+, Zn2+) mg L-1 of the potentially bioavailable metal ions and over 17¿mg¿L-1 metal levels was lethal for the microbe. Further, it could fix 217¿274¿µg¿mL-1 of N and solubilize 79¿135¿µg¿mL-1 of P while PAHs degradation. MTS-7 as a superior candidate could be thus used in the enhanced bioaugmentation and/or phytoremediation of long-term mixed contaminated sites.

We reported the Australian golden wattle as a copper stabilizer in abandoned copper mine soils earlier. Here we investigate to confirm this plant's suitability to grow on metal contaminated mine soils based on stress indication. The seeds of Acacia pycnantha collected from mining area were germinated after heat and no heat treatment on two types of irrigation. The daily irrigated and heat treated seeds gave up to 85% germination on sandy soil. The A. pycnantha was grown under greenhouse condition in six different soils collected from abandoned copper mine at Kapunda in South Australia. Among the six soil samples, soil-1 with the highest copper concentration produced 2.05 mmol g-1 tissue of proline. Proline expression was prominent in more saline soils (1, 5 and 6) having electrical conductivity (EC) 1184, 1364 and 1256 µS, respectively. Chlorophyll a, b and carotenoid levels in plants showed a gradually decreasing trend in all the soils as experiment progressed. The plants grown on soil sample-1, containing 4083 ± 103 mg kg-1 of copper resulted in 18 ± 2 mg kg-1 accumulation in its leaf. The calcium accumulation was significant up to 11648 ± 1209 mg kg-1 in leaf. Although pore water samples showed higher Cu concentration in soils, an increased mobility of arsenic and lead was observed in all the soil samples. Our experiment points out the need for proper monitoring of revegetation processes to avoid revegetation and reclamation failure.