Associate Professor Geoff MacFarlane

The Sundarbans is the largest single-mass mangrove forest in the world, experiencing environmental and anthropogenic stress from metal(loid) inputs. We undertook a comprehensive assessment of sediment contamination and ecological risks posed by metal(loid)s in the Sundarbans using previously published data. There was a distinct difference in metal(loid) content, pollution level and ecological risk in Bangladeshi and Indian parts of the Sundarbans, with the Indian counterpart experiencing relatively higher metal(loid) pollution. The higher pollution level in India might be attributed to its vicinity to municipal and industrial areas that act the primary source of metal(loid)s in the Sundarbans. The cumulative ecological risks of metal(loid)s pointed out that the south-eastern part of Bangladeshi Sundarbans and north-eastern Indian part are at moderate ecological risk. This research will provide valuable data to inform the responsible authorities and will underpin future policies and management to reduce future metal(loid) inputs in the Sundarbans.

Metal contamination is a global issue impacting biodiversity in urbanised estuaries. Traditional methods to assess biodiversity are time consuming, costly and often exclude small or cryptic organisms due to difficulties with morphological identification. Metabarcoding approaches have been increasingly recognised for their utility in monitoring, however studies have focused on freshwater and marine systems despite the ecological significance of estuaries. We targeted estuarine eukaryote communities within the sediments of Australia's largest urbanised estuary, where a history of industrial activity has resulted in a metal contamination gradient. We identified specific eukaryote families with significant correlations with bioavailable metal concentrations, indicating sensitivity or tolerance to specific metals. While polychaete families Terebellidae and Syllidae demonstrated tolerance to the contamination gradient, members of the meio- and microfaunal communities including diatoms, dinoflagellates and nematodes displayed sensitivities. These may have high value as indicators but are frequently missed in traditional surveys due to sampling limitations.

Halophytes residing in metal-contaminated saltmarsh habitats may employ strategies to enhance fitness of the next generation. We aimed to test the hypothesis that Juncus acutus individuals inhabiting metal-contaminated locations would experience elevated tolerance of offspring to metals compared to plants residing in locations with no metal contamination history. J. acutus seeds (F1 generation) were collected from F0 parent plants residing at eight locations of a contemporary sediment metal gradient (contaminated to uncontaminated) across the coast of NSW, Australia (Hunter river, Lake Macquarie and Georges River). Seeds were exposed in the laboratory to incremental Zn (0.0¿1.6 mM) and Pb (0.0¿0.50 mM) for nine (9) days, and % germination, germination rate, root elongation and vigour index were assessed for the determination of tolerance. Greater root accumulation (BCF = 1.01) of Zn and subsequent translocation to aerial parts (culm BCF = 0.58 and capsule BCF = 0.85) were exhibited in parents plants, whereas Pb was excluded from roots (BCF = 0.60) and very little translocation to aerial portions of the plant was observed (culm BCF = 0.02 and capsule BCF = 0.05). F1 offspring exhibited tolerance to Zn with EC50 (% germination) significantly correlated with their parents' culm (R2 = 0.93, p = 0.00) and capsule (R2 = 0.57; p = 0.03) Zn. No correlations were observed between offspring Pb tolerance and Pb in parents¿ plant tissues. Enhanced tolerance to the essential metal Zn may be because Zn is very mobile in the parent plant and seeds experience greater Zn load as a significant portion of sediment Zn reaches capsules (85%). Thus, Zn tolerance in J. acutus seeds is likely attributable to acclimation via maternal transfer of Zn; however, further manipulative experiments are required to disentangle potential acclimation, adaptation or epigenetic effects in explaining the tolerance observed.

This study aimed to reveal possible alterations to lipidomic profiles in Sydney rock oysters, Saccostrea glomerata, exposed to estrogenic mixtures (i.e., estrone, E1; 17ß-estradiol, E2; estriol, E3; 17a-ethinylestradiol, EE2; bisphenol A, BPA; 4-t-octylphenol, 4-t-OP; and 4-nonylphenol, 4-NP) at ¿low¿ and ¿high¿ concentrations, typical of those detected in Australian and global receiving waters. A seven-day acute exposure window exhibited significantly lower abundances of many non-polar metabolites in digestive gland, gills, and gonads. Overall, there was a strong effect of the carrier solvent ethanol (despite a low exposure of 0.0002%), with all solvent containing treatments exhibiting lower abundances of lipidic metabolites, especially in the gill and digestive gland. No significant changes of the lipidome were exhibited in the male gonad by estrogenic exposure. However, in the female gonad, significant reductions of phospholipids and phosphatidylcholine were associated with exposure to high estrogenic mixtures. We hypothesise that the decreases in these phospholipids in the female gonad may be attributable to 1) lower algal consumption and thus lower uptake of lipidic building blocks; 2) a reduction of available substrates for phospholipid and phosphatidylcholine synthesis; and/or 3) induction of reactive oxygen species via estrogen metabolism, which may cause lipid peroxidation and lower abundance of phospholipids.

This study assessed the appropriate sampling design required for quantifying variability in metal accumulation in the leaf tissues of A. marina, a dominant mangrove inhabiting Australian estuaries, by applying a hierarchical nested sampling design to sample mangroves at various levels of biological and spatial hierarchies (leaf, branch, tree, site). It was revealed that most variation in metal accumulation occurred among trees and branches, with insignificant variation between sites and among leaves. We also examined the accumulation of metal (loid)s in the leaf tissues collected from six locations across the Georges River estuary in southern Sydney, which differ in metal contamination history. Prospect Creek and Salt Pan Creek were the most contaminated locations, which exceeded sediment quality guideline values for Cu (66.71 ± 2.18 µg/g), Zn (317.14 ± 46.14 µg/g) and Pb (81.02 ± 2.79 µg/g). All metal(loid) concentrations in leaf tissues were much lower than their concentrations in sediment, but essential metals exhibited greater mobility. Out of 10 metal(loid)s, Mn, Co and Pb in leaves showed linear relationships (R2 = 0.28¿0.47) with sediment, indicating that mangrove leaves may be used as a bioindicator of environmental loads for these metals.

Estuaries are critical habitats subject to a range of stressors requiring effective management. Microbes are gaining recognition as effective environmental indicators, however, the response of host associated communities to stressors remains poorly understood. We examined microbial communities from seawater, sediments and the estuarine fish Pelates sexlineatus, in Australia's largest urbanised estuary, and hypothesised that anthropogenic contamination would be reflected in the microbiology of these sample types. The human faecal markers Lachno3 and HF183 were not detected, indicating negligible influence of sewage, but a gradient in copy numbers of the class 1 integron (intI-1), which is often used as a marker for anthropogenic contamination, was observed in sediments and positively correlated with metal concentrations. While seawater communities were not strongly driven by metal contamination, shifts in the diversity and composition of the fish gut microbiome were observed, with statistical links to levels of metal contamination (F2, 21 = 1.536, p < 0.01). Within the fish gut microbiome, we further report increased relative abundance of amplicon sequence variants (ASVs; single inferred DNA sequences obtained in sequencing) identified as metal resistant and potentially pathogenic genera, as well as those that may have roles in inflammation. These results demonstrate that microbial communities from distinct habitats within estuarine systems have unique response to stressors, and alterations of the fish gut microbiome may have implications for the adaptation of estuarine fish to legacy metal contamination.

An impact assessment of oceanic effluent releases from Belmont wastewater treatment works (WWTW) in Newcastle, Australia, was undertaken. Benthic infaunal assemblages in sandy sediments of ~25 m water depth were examined, at sites adjacent to the release point, and at increasing distances up to 2 km in both a NE and SW direction over five consecutive years (2016¿2020). Localised impacts were evident for infaunal assemblages, with sites within 20 m of the outfall (¿Impact¿ site types) exhibiting lower taxa richness and Shannon diversity, higher abundances of polychaetes and/or nematodes, higher polychaete ratios, and shifts in assemblage composition in comparison to sites at greater distances during some years. Taxa with increased localised abundances at the outfall were identified as indicators for monitoring impacts, including deposit-feeding polychaetes (Families Polygordiidae, Paraonidae and Dorvilleidae) and Phylum Nematoda. Future infaunal monitoring could include molecular tools and paired sediment analyses.

The current study represents the first attempt to analyse quantitatively, within a phylogenetic framework, uptake and partitioning patterns of copper (Cu), zinc (Zn), cadmium (Cd) and lead (Pb) in extant saltmarsh taxa globally, and to assess associations of these patterns with various plant traits indicative of their halophytic adaptations. Despite saltmarsh being diverse taxonomically, most saltmarsh taxa accumulate metals to roots at, or above, unity (> 1). Further, there is significant translocation from roots to shoot for Cu, Zn and Cd (= 1), however, Pb is less mobile (TF = 0.65). Patterns of accumulation were similar among families, except greater Cd accumulation to roots in members of Juncaceae. Patterns of uptake to roots and translocation to leaves were broadly similar among plant type, plant form, habitat and photosynthetic mode. Zinc is lower in the leaves of salt-secreting species for some closely related taxa, suggesting some species co-excrete sodium (Na+) and Zn2+ through glands in leaf tissue. Salinity tolerance has no relationship to metal uptake and translocation. Translocation of Zn is greater at lower Zn sediment exposures, reflecting its active uptake and essentiality, but such bias does not affect outcomes of analyses when included as a covariate.

Estrogenic compounds enter waterways via effluents from wastewater treatment works (WWTW), thereby indicating a potential risk to organisms inhabiting adjacent receiving waters. However, little is known about the loads or concentrations of estrogenic compounds that enter Australian WWTWs, the efficiency of removing estrogenic compounds throughout the various stages of tertiary WWTW processes (which are common in Australia), nor the concentrations released into estuarine or marine receiving waters, and the associated risk for aquatic taxa residing in these environments. Therefore, seven estrogenic compounds, comprising the natural estrogens estrone (E1), 17ß-estradiol (E2) and estriol (E3), the synthetic estrogen (EE2), and the industrial chemicals bisphenol A (BPA), 4-t-octyl phenol (4-t-OP) and 4-nonyl phenol (4-NP), in wastewater samples were quantified via liquid chromatographic-mass spectrometry (LC-MS) after solid-phase extraction at different stages of wastewater treatment and associated receiving waters. The concentrations of the target compounds in wastewater ranged from < LOQ (limit of quantification) to 158 ng/L for Tanilba Bay WWTW and < LOQ to 162 ng/L for Belmont WWTW. Most target compounds significantly declined after the secondary treatment phase. Appreciable removal efficiency throughout the treatment process was observed with removal from 39.21 to 99.98% of influent values at both WWTWs. The reduction of the natural estrogens (E1, E2 and E3) and 4-t-OP were significantly greater than EE2, BPA, and 4-NP in both WWTWs. Risk quotients (RQs) were calculated to assess potential ecological risks from individual estrogenic compounds. In predicted diluted effluents, no targeted compounds showed any ecological risk (RQ =1.65 × 10-2) at both WWTWs. Similarly, all RQs for shore samples at both WWTWs were below 1. Finally, the hazard index (HI), which represents combined estrogenic contaminants¿ ecological risk, indicated no mentionable risk for predicted diluted effluents (HI = 0.0097 to 0.0218) as well as shoreline samples (HI = 0.393 to 0.522) in the receiving estuarine or marine waters.

Anthropogenic metal pollution remains a substantial threat to remnant saltmarsh ecosystems as they continue to decline globally. Metal pollutants impart sublethal stress on saltmarsh halophytes evident at transcriptomic, proteomic, metabolomic and physiological levels. Halophytes form the basal underpinning of saltmarsh ecosystems and as such changes to their physiology may have subsequent detrimental effects on higher levels of ecological organisation. This concept forms the basis of a mechanistic framework for toxicity: an adverse outcome pathway (AOP). AOPs facilitate the use of molecular and biological markers to predict consequent effects on population parameters, and community structure and function. We reviewed the current literature on common anthropogenically enhanced metals (Cu, Zn, Cd and Pb) in saltmarsh ecosystems internationally. The literature amassed to date indicates a lack of data in regard to the impacts of metals at higher levels of biological organisation and insufficient relevant data available to develop reliable AOPs. Collectively, metals impart sublethal stress at the transcriptomic, proteomic, and metabolomic levels and targets of toxic effect are predominantly biomolecules involved in metal transport and detoxification, antioxidant pathways associated with metal-induced oxidative stress, and photosynthetic biochemistry. Thus, these targets would be useful biomarkers in future studies designed to develop AOPs in saltmarsh taxa.

We examined the patterns of uptake and partitioning of metal(loid)s in Suaeda australis from three highly urbanised estuaries (Sydney Olympic Park, Hunter Wetlands and Lake Macquarie) in NSW, Australia. Of these, Sydney Olympic Park was found to be the most contaminated estuary in terms of combined sediment metal(loid) load, followed by Hunter Wetlands and lowest in Lake Macquarie (via PERMANOVA). Uptake in roots was greater for the essential metals Cu and Zn along with the non-essential metal Cd and the metalloid Se (root BCFs >1) and lower for Pb and As (root BCFs <1). Substantial barriers for translocation from roots to stems were identified for all metal(loid)s (stem TFs; 0.07¿0.68). Conversely, unrestricted flow from stems to leaves was observed for all metal(loid)s at unity or higher (leaf TFs = 1). Strong linear relationships between sediment and root for Zn and Pb were observed, indicating roots as a useful bioindicator.

Marine molluscs, such as oysters, respond to estrogenic compounds with the induction of the egg yolk protein precursor, vitellogenin (Vtg), availing a biomarker for estrogenic pollution. Despite this application, the precise molecular mechanism through which estrogens exert their action to induce molluscan vitellogenesis is unknown. As a first step to address this question, we cloned a gene encoding Vtg from the Sydney rock oyster Saccostrea glomerata (sgVtg). Using primers designed from a partial sgVtg cDNA sequence available in Genbank, a full-length sgVtg cDNA of 8498 bp was obtained by 5'- and 3'-RACE. The open reading frame (ORF) of sgVtg was determined to be 7980 bp, which is substantially longer than the orthologs of other oyster species. Its deduced protein sequence shares the highest homology at the N- and C-terminal regions with other molluscan Vtgs. The full-length genomic DNA sequence of sgVtg was obtained by genomic PCR and genome walking targeting the gene body and flanking regions, respectively. The genomic sequence spans 20 kb and consists of 30 exons and 29 introns. Computer analysis identified three closely spaced half-estrogen responsive elements (EREs) in the promoter region and a 210-bp CpG island 62 bp downstream of the transcription start site. Upregulation of sgVtg mRNA expression was observed in the ovaries following in vitro (explants) and in vivo (tank) exposure to 17ß-estradiol (E2). Notably, treatment with an estrogen receptor (ER) antagonist in vitro abolished the upregulation, suggesting a requirement for an estrogen-dependent receptor for transcriptional activation. DNA methylation of the 5' CpG island was analysed using bisulfite genomic sequencing of the in vivo exposed ovaries. The CpG island was found to be hypomethylated (with 0-3% methylcytosines) in both control and E2-exposed oysters. However, no significant differential methylation or any correlation between methylation and sgVtg expression levels was observed. Overall, the results support the possible involvement of an ERE-containing promoter and an estrogen-activated receptor in estrogen signalling in marine molluscs.

Soil in urban areas contains the residues of past land-uses and practices. Urban farming (keeping chickens, vegetable gardening) requires soil disturbance and can increase exposure of residents to these contaminants. We measured the level of lead, arsenic, cadmium, copper and zinc contaminants in soil and eggs from 26 backyard chicken coops across the Lower Hunter, NSW Australia. We compared the levels of metals in soil to Health Investigation Levels and metals in home-grown eggs to the levels in commercial eggs tested in this study or published by Food Standards Australia New Zealand. The levels of arsenic, cadmium, copper and zinc were low, both in soil and in home-grown eggs and were comparable to commercial eggs tested in this study. The Health Investigation Level for lead in soil (300 mg lead/kg soil) was exceeded at 7 of the 26 sites. The level of lead in home-grown eggs was generally higher than in commercial eggs. The reference health standard for meat (including chicken), fruit and vegetables of 0.1 mg lead/kg produce was exceeded in home-grown eggs from 7 of the 26 sites. There was a significant relationship between the lead level in eggs and the lead level in soil accessible to chickens. As soil lead increased, concentrations of lead in eggs tended to increase. No relationship was detected between the lead level in feed and in eggs. We recommend strategies to reduce ingestion of soil by chickens thereby reducing metal contamination in home-grown eggs.

Same-sex genital interactions (SSGIs) occur across the order primates, yet explaining their maintenance in evolutionary terms appears problematic; as such interactions seem to counteract reproductive goals. We hypothesised that in more promiscuous species, where sexual motivation, mating effort, and non-conceptive heterosexual behaviour are greater, SSGIs may also occur at greater frequencies without necessarily impeding reproduction. We found that the expression of both male and female SSGIs were greater in multimale systems than in unimale ones. Both male and female SSGIs were positively correlated with the degree of promiscuity (relative testes mass). As mating system confers biases in the sex ratio that may influence the expression of SSGIs, we controlled for availability of members of the same-sex. When employing this control, results were largely congruent. For males, SSGIs were expressed more frequently in multimale systems. For both sexes, SSGIs were expressed more frequently with greater relative testes mass. We suggest SSGIs in primates may be a neutral by-product of selection for increases in promiscuous sexual activity, and that in certain instances these interactions may be co-opted to facilitate adaptive social functions.

Mangroves have been observed to possess a tolerance to high levels of heavy metals, yet accumulated metals may induce subcellular biochemical changes, which can impact on processes at the organism level. Six month-old seedlings of the grey mangrove, Avicennia marina (Forsk.) Vierh, were exposed to a range of Cu (0-800 µg/g), Pb (0-800 µg/g) and Zn (0-1000 µg/g) concentrations in sediments under laboratory conditions, to determine leaf tissue metal accumulation patterns, effects on photosynthetic pigments (chlorophyll a, chlorophyll b and carotenoids), and the activity of the antioxidant enzyme peroxidase. Limited Cu uptake to leaves was observed at low sediment Cu levels, with saturation and visible toxicity to Cu at sediment levels greater than 400 µg/g. Leaf Pb concentrations remained low over a range of Pb sediment concentrations, up to 400 µg/g Pb, above which it appeared that unrestricted transport of Pb occurred, although no visible signs of Pb toxicity were observed. Zn was accumulated linearly with sediment zinc concentration, and visible toxicity occurring at the highest concentration, 1000 µg/g Zn. Significant increases in peroxidase activity and decreases in photopigments were found with Cu and Zn at concentrations lower than those inducing visible toxicity. Significant increases in peroxidase activity only, were found when plants were exposed to Pb. Positive linear relationships between peroxidase activity and leaf tissue metal concentrations were found for all metals. Significant linear decreases in photosynthetic pigments with increasing leaf tissue metal concentrations were observed with Cu and Zn only. Photosynthetic pigments and peroxidase activity may be applicable as sensitive biological indicators of Cu and Zn stress, and peroxidase activity for Pb stress in A. marina. Copyright © 2001 Elsevier Science Ltd.

Macrobenthic community assemblage diversity and abundance were monitored on both Cowan and Berowra Creeks in the estuarine reaches of the Hawkesbury River, Sydney Australia during 1997-1998. Natural sediment physicochemical differences were assessed, along with low-level anthropogenic contaminants including copper, lead, zinc, phosphorus and nitrogen. Contaminant levels at all sites were below sediment guideline values for biological effects. Natural physicochemical sediment differences were the main determinants in species assemblage patterns among sites. Three groupings of sites with similar assemblages were observed during February 1998. Berowra Creek sites, which were higher in organic content and silt/clay (and thus metals and nutrients), higher in pH and lower in salinity, were similar in terms of contributions by the polychaetes Ceratoneresis aequisetis, Scoloplos normalis, the isopod Cyathura hakea and the bivalve mollusc Soletellina alba. Sites on upper Cowan Creek, higher in organic content, silt/clay (nutrients and metals) and lower in salinity, were similar and separated from other sites in terms of the polychaete Carazziella victoriensis and the gastropod mollusc Nassarius jonasii. Sites lower in Cowan Creek, tended to be higher in sand content, more saline and lower in organic content and thus nutrient and metal concentrations. These sites were similar in terms of contributions of the polychaete Sigalion bandaensis and the bivalve molluscs, Mysella vitrea and Tellina deltoidalis. The biotic assemblage patterns were not maintained temporally, suggesting the importance of monitoring over time to assess possible future impacts. Aggregating species data to the family level resulted in similar site discrimination. Site differences were less distinct at higher taxonomic levels and suggests future monitoring at the family level is sufficient to detect assemblage differences among sites. The results obtained represent the difficulty in detecting responses to low-level contamination at the community level, and provide a sound anticipatory baseline for the assessment of future possible anthropogenic disturbance in the Hawkesbury River.

Although alterations at the organism level in decapod crustaceans on exposure to heavy metals have been evidenced in the laboratory, little examination of metal effects on morphology and population parameters have been explored in a field-based situation. Relationships between morphological parameters, population demography and heavy metal sediment loadings were examined in conjunction with the accumulation of metals in the Semaphore crab, Heloecius cordiformis, in the Port Jackson and Hawkesbury River estuaries, Sydney, Australia. H. cordiformis exhibited sexual dimorphism, with males having larger carapace width, carapace length, chelae length and total mass than females. Sexes were subsequently treated separately to assess morphological differences among locations. Locations that had greater proportions of females with purple chelae and less females in the population tended to have higher sediment metal levels. These relationships were maintained over time, and could be employed as population-level biological indicators of heavy metal stress. Copper and zinc were regulated in the hepatopancreas of H. cordiformis. Lead was accumulated in the hepatopancreas of H. cordiformis in proportion to sediment lead levels, suggesting the species is both an appropriate candidate for bio-indication of lead pollution, and Pb is the main metal linked with population level differences. Accumulation of lead varied between sexes, indicating that sexes must be monitored separately. Smaller males accumulated more lead than larger males, suggesting size is an important consideration for lead accumulation. (C) 2000 Elsevier Science B.V.

The distribution and excretion of Cu, Pb and Zn in the root and leaf tissue of the grey mangrove, Avicennia marina was studied using scanning electron microscope (SEM) X-ray microanalysis and atomic absorption spectroscopy. SEM X-ray microanalysis of nutritive root tissue in seedlings dosed with 4 g/l Cu, Pb and Zn revealed accumulation of all metals predominantly in cell walls. The root epidermis provided a major barrier to the transport of Pb only. The endodermal casparian strip was shown to provide a barrier to movement of all three metals into the stele. Washings from mature leaves contained significantly higher amounts of Zn and Cu than control plants after 1 month, suggesting excretion of both metals from the glandular trichomes. In addition, salt crystals exuded from the glands on the adaxial surface of mature leaves were composed of alkaline metals: Zn in Zn-treated plants, and Cu in Cu-treated plants. Leaf tissue in seedlings dosed with 4 g/l Zn showed a decreasing gradient of the metal from xylem tissue, through photosynthetic mesophyll, to hypodermal (water) tissue, with a subsequent increase in concentration in the glandular tissue. A similar gradient was observed across leaf tissue in seedlings dosed with 4 g/l Cu, however, there was no subsequent increase in Cu concentration in glandular tissue. For both metals leaf cell wall metal concentrations were consistently higher than intracellular concentrations. (C) 2000 Elsevier Science B.V.

The New South Wales Olympic Co-ordination Authority, which is responsible for the redevelopment of the site for the Olympic Games 2000, Sydney, is committed to the rehabilitation of the remnant ecosystems remaining on the site. This paper describes a 3-year saltmarsh transplantation project, and resulting management approaches for the rehabilitation of other saline wetland areas on the site. Two series of cuttings (spring and autumn) were made, including three dominant species and three species rare in Sydney. It was found that all the species could be propagated without difficulty, but field survival and growth were much higher for the spring series than the autumn one. Measurement was also made of the colonisation of mangrove and saltmarsh species that occurred at the site over the course of the trials. New understandings of estuarine wetland colonisation have emerged, and the information has been used to develop methods of transplantation for other parts of the Olympic site, and to define management needs for monitoring success.

The Homebush Bay area, Sydney, site of the Olympic Games 2000, has been largely occupied for nearly a century by an abattoir, brickworks, armaments depot and waste dumps. However, it contains remnants of original ecosystems, including two estuarine wetlands, and the Olympic Co-ordination Authority (OCA), set up to manage the redevelopment of the site, is committed to the rehabilitation of these ecosystems. The ecological approaches and rehabilitation measures used for one of the wetlands are detailed. Apart from a history of disturbance, it has for 10 years been without tidal flushing. However, these wetlands are the largest remaining in the Sydney estuary, and are significant for a number of reasons including biodiversity and waterbird conservation. The ecological parameters of the site, the results of a 'before-restoration-impact' study , and the iterative links between science and management in the introduction of the rehabilitation measures, are presented. Criteria for success are discussed, along with biomonitoring strategies to test success.

Mangroves are important as primary producers in estuarine food chains. Zinc is often a major anthropogenic contaminant in estuarine ecosystems and has potential ecotoxicological consequences for mangrove communities. Accumulation, distribution and excretion of zinc in the leaf tissue of the grey mangrove, Avicennia marina was studied using SEM X-ray microanalysis and Atomic Absorption Spectroscopy. The first leaves of A. marina grown in 500 µg Zn as ZnCl2 per g of dry soil were found to accumulate 106.3 ± 18.5 µg Zn per g dry tissue, significantly higher than control plants, after a 7-month period. Washings from first leaves contained significantly higher amounts of zinc (0.30 ± 0.14 µg/cm2 Zn) than control plants after 1 month, suggesting excretion of zinc from glandular trichomes. SEM X-ray microanalysis revealed salt crystals exuded from glandular tissue on the adaxial surface of first leaves to be composed of alkaline metals and zinc in zinc treated plants. SEM X-ray microanalysis of seedlings dosed with 4 g/l Zn as Zn Cl2 revealed a decreasing Zn gradient from xylem tissue, through photosynthetic mesophyll, to hypodermal (water) tissue. A subsequent increase in Zn concentration was observed in glandular tissue. Cell wall Zn concentrations were consistently higher than intracellular Zn concentrations.