Dr Md Meftaul Islam

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.]

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.

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.

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.