Mercury In Aquatic Environment Research Articles

Interaction of Naturally Occurring Phytoplankton with the Biogeochemical Cycling of Mercury in Aquatic Environments and Its Effects on Global Hg Pollution and Public Health.

The biogeochemical cycling of mercury in aquatic environments is a complex process driven by various factors, such as ambient temperature, seasonal variations, methylating bacteria activity, dissolved oxygen levels, and Hg interaction with dissolved organic matter (DOM). As a consequence, part of the Hg contamination from anthropogenic activity that was buried in sediments is reinserted into water columns mainly in highly toxic organic Hg forms (methylmercury, dimethylmercury, etc.). This is especially prominent in the coastal shallow waters of industrial regions worldwide. The main entrance point of these highly toxic Hg forms in the aquatic food web is the naturally occurring phytoplankton. Hg availability, intake, effect on population size, cell toxicity, eventual biotransformation, and intracellular stability in phytoplankton are of the greatest importance for human health, having in mind that such Hg incorporated inside the phytoplankton cells due to biomagnification effects eventually ends up in aquatic wildlife, fish, seafood, and in the human diet. This review summarizes recent findings on the topic of organic Hg form interaction with natural phytoplankton and offers new insight into the matter with possible directions of future research for the prevention of Hg biomagnification in the scope of climate change and global pollution increase scenarios.

Identification of Mercury in Tembang Fish (Sardinella gibbosa) and Shellfish (Marcia hiantina) in Losari Coastal Beach, Makassar

Mercury was one of heavy metals that became pollutant. High level of mercury in aquatic environment could cause adverse effects on living organisms in that environment, even endanger human health in using the water and consuming the organism. This reasearch was a descriptive survey that was supported by laboratory test result in order to know mercury (Hg) level in Tembang fish (Sardinella gibbosa) and Shellfish (Marcia hiantina) in Losari coastal beach, Makassar. The result of mercury examination at Center Health Laboratory Makasar was obtained that mercury levels in Tembang Fish were 0.0150 mg/kg, 0.0133 mg/kg and 0.0126 mg/kg. Thus, the average of mercury level in Tembang fish was 0.0409 mg/kg. Meanwhile, based on examination results of mercury level in Shellfish at Center Health Laboratory, Makasar, were obtained 0.0228 mg/kg, 0.0266 mg/kg, and 0.1105 mg/kg. Thus, the average of mercury level in Shellfish was 0.1599 mg/kg. Moreover, mercury level in either Tembang fish or Shellfish in Losari coastal beach Makassar had fulfilled the requirement based on SNI 7387/2009 regarding Maximum Limit of Heavy Metal of Mercury. Keywords: Mercury, Shellfish, Tembang Fish

Mercury: Biogeochemical and Toxicological Aspects and Levels Found in Marine Fish Along the Southern and Southeastern Coasts of Brazil

Sources of mercury (Hg ) introduced into the environment can be natural or anthropogenic. Methylmercury (MeHg ) is the most toxic form of the mercury, and is responsible for detrimental e ects on human health through the consumption of food, notably marine vertebrates such as carnivorous fish and sharks. is review focuses on aspects related to biogeochemistry and ecotoxicology of mercury in aquatic environments and presents 12 studies with sh in the Southern Brazilian coast marine environment where 50% of the sh sampled had Hg concentrations, above the level established by national and international agencies as safe for human consumption.

Successful New Methodology for Isotachophoretic Technique Determination of Mercury

This work presents a step-by-step study of a new methodology for capillary isotachophoretic determination (which is one of the green chemistry techniques) of mercury in aquatic environments. Hundreds of analyses resulted in the identification of optimal conditions for the determination of mercury(II) and the identification of problems related to such determination. Recovery for the analyzed compounds was 94 ± 4%, linearity of the method was between 10 and 75 µg/L, and detection limit was 5 µg/L.

Phytoremediation of water contaminated with mercury using Typha domingensis in constructed wetland

The presence of mercury in aquatic environments is a matter of concern by part of the scientific community and public health organizations worldwide due to its persistence and toxicity. The phytoremediation consists in a group of technologies based on the use of natural occurrence or genetically modified plants, in order to reduce, remove, break or immobilize pollutants and working as an alternative to replace conventional effluent treatment methods due to its sustainability – low cost of maintenance and energy. The current study provides information about a pilot scale experiment designed to evaluate the potential of the aquatic macrophyte Typha domingensis in a constructed wetland with subsurface flow for phytoremediation of water contaminated with mercury. The efficiency in the reduction of the heavy metal concentration in wetlands, and the relative metal sorption by the T. domingensis, varied according to the exposure time. The continued rate of the system was 7 times higher than the control line, demonstrating a better performance and reducing 99.6±0.4% of the mercury presents in the water contaminated. When compared to other species, the results showed that the T. domingensis demonstrated a higher mercury accumulation (273.3515±0.7234mgkg−1) when the transfer coefficient was 7750.9864±569.5468Lkg−1. The results in this present study shows the great potential of the aquatic macrophyte T. domingensis in constructed wetlands for phytoremediation of water contaminated with mercury.

Nrf2b, Novel Zebrafish Paralog of Oxidant-responsive Transcription Factor NF-E2-related Factor 2 (NRF2)

NF-E2-related factor 2 (NRF2; also called NFE2L2) and related NRF family members regulate antioxidant defenses by activating gene expression via antioxidant response elements (AREs), but their roles in embryonic development are not well understood. We report here that zebrafish (Danio rerio), an important developmental model species, possesses six nrf genes, including duplicated nrf1 and nrf2 genes. We cloned a novel zebrafish nrf2 paralog, nrf2b. The predicted Nrf2b protein sequence shares several domains with the original Nrf2 (now Nrf2a) but lacks the Neh4 transactivation domain. Zebrafish-human comparisons demonstrate conserved synteny involving nrf2 and hox genes, indicating that nrf2a and nrf2b are co-orthologs of human NRF2. nrf2a and nrf2b displayed distinct patterns of expression during embryonic development; nrf2b was more highly expressed at all stages. Embryos in which Nrf2a expression had been knocked down with morpholino oligonucleotides were more sensitive to tert-butylhydroperoxide but not tert-butylhydroquinone, whereas knockdown of Nrf2b did not affect sensitivity of embryos to either chemical. Gene expression profiling by microarray identified a specific role for Nrf2b as a negative regulator of several genes, including p53, cyclin G1, and heme oxygenase 1, in embryos. Nrf2a and Nrf2b exhibited different mechanisms of cross-talk with the Ahr2 signaling pathway. Together, these results demonstrate distinct roles for nrf2a and nrf2b, consistent with subfunction partitioning, and identify a novel negative regulatory role for Nrf2b during development. The identification of zebrafish nrf2 co-orthologs will facilitate new understanding of the multiple roles of NRF2 in protecting vertebrate embryos from oxidative damage.

GENOTOXIC EFFECTS OF METHYLMERCURY ON THE FISH <i>Colossoma macropomum</i> (CHARACIFORMES: CHARACIDAE) AS EVALUATED USING THE COMET ASSAY

Comet assay has been used increasingly to evaluate genotoxicity of many metals and their organic compounds in aquatic ecosystems. The use of endemic aquatic organisms as biological sentinels has proved to be useful to environmental monitoring. In this study, the genetic damages caused by methylmercury (MeHg) in the widely distributed Amazonian fish, Colossoma macropomum (commonly called tambaqui), was assessed using the comet assay. Specimens of C. macropomum were acclimatized in aquariums to laboratory conditions and then exposed to 2mg.L-1 MeHg by hydric way. Peripheral blood samples were obtained from specimens and subjected to the comet assay. Exposure to MeHg significantly increased the frequency of tailed nucleoids in the erythrocytes of fishes exposed (p C. macropomum is not only important as eatable species, but also an adequate model for biological studies that evaluate genotoxic effects of mercury in aquatic environments.

Mercury reduction and complexation by natural organic matter in anoxic environments

Mercuric Hg(II) species form complexes with natural dissolved organic matter (DOM) such as humic acid (HA), and this binding is known to affect the chemical and biological transformation and cycling of mercury in aquatic environments. Dissolved elemental mercury, Hg(0), is also widely observed in sediments and water. However, reactions between Hg(0) and DOM have rarely been studied in anoxic environments. Here, under anoxic dark conditions we show strong interactions between reduced HA and Hg(0) through thiolate ligand-induced oxidative complexation with an estimated binding capacity of ~3.5 μmol Hg/g HA and a partitioning coefficient >10(6) mL/g. We further demonstrate that Hg(II) can be effectively reduced to Hg(0) in the presence of as little as 0.2 mg/L reduced HA, whereas production of Hg(0) is inhibited by complexation as HA concentration increases. This dual role played by DOM in the reduction and complexation of mercury is likely widespread in anoxic sediments and water and can be expected to significantly influence the mercury species transformations and biological uptake that leads to the formation of toxic methylmercury.

Characterization of sorption gels used for determination of mercury in aquatic environment by diffusive gradients in thin films technique

Abstract The influence of pH, ionic strength and selected natural ligands on the measurement of mercury by the diffusive gradients in thin films technique (DGT) using recently introduced sorption gels was determined. Sorption gels containing Chelex 100, Spheron-Thiol, Duolite GT73 and modified Iontosorb AV resins were investigated, with the sorption capacity determined for all used sorption gels. The minimum DGT measurable concentrations were calculated from 3 times the standard deviation of mercury amount in unexposed sorption gels.

Detection of Mercury in Aquatic Environments Using EPRE Reporter Zebrafish

It has been proposed that transgenic zebrafish could be designed to detect low levels of chemical contaminants that cause oxidative stress in aquatic environments, such as heavy metals or pesticides. In this paper, we describe such a transgenic zebrafish that produces a luciferase-green fluorescent protein (LUC-GFP) fusion protein under conditions of oxidative stress. The reporter gene expression is under the regulation of the electrophile responsive element (EPRE), which activates gene expression in response to oxidative stressors. The GFP component of this fusion protein allows us to visually detect reporter gene activity in live animals to determine if activity is localized to a particular tissue. The luciferase component is capable of returning a quantitative assessment of reporter gene activity that allows us to determine if reporter gene activity is directly correlated to the concentration of the chemical inducer. We have tested this reporter construct in both transient and stable transgenic fish after exposure to a range of HgCl(2) concentrations. GFP expression from the EPRE-LUC-GFP construct was inducible in transient assays but was below the limit of detection in stable lines. In contrast, we observed inducible luciferase activity in both transient assays and stable lines treated with HgCl(2). We conclude that the EPRE is capable of driving reporter gene expression in a whole animal assay under conditions of oxidative stress. Furthermore, expression was induced at HgCl(2) concentrations that do not result in obvious morphological defects, making this approach useful for the detection of low levels of oxidative contaminants in aquatic environments.

Development and test application of a screening-level mercury fate model and tool for evaluating wildlife exposure risk for surface waters with mercury-contaminated sediments (SERAFM)

Complex chemical cycling of mercury in aquatic ecosystems means that tracing the linkage between anthropogenic and natural loadings of mercury to watersheds and water bodies and associated concentrations in the environment are difficult to establish without the assistance of numerical models that describe biogeochemical controls on mercury distribution and availability to organisms. This paper presents an overview of a process-based, steady-state model developed for state and water quality managers and scientists to assist in ecological risk assessments for mercury in aquatic environments. SERAFM (Spreadsheet-based Ecological Risk Assessment for the Fate of Mercury) incorporates the chemical, physical, and biological processes governing mercury transport and fate in a surface water including atmospheric deposition, watershed transport and transformation, solid transport and cycling within the water body, and water body mercury processes. This modelling framework was designed to assist risk assessors in evaluating wildlife risk at the screening-level for an aquatic ecosystem with mercury-contaminated sediments. An example application of the model that is used to inform a regional risk assessment is presented in this manuscript. In the example provided, hazard quotients for exposed wildlife and humans are calculated by the model for three scenarios: historical case of mercury-contaminated sediments, required clean-up levels to protect the most sensitive species, and background conditions. The spreadsheet structure of SERAFM permits dismantling and reassembling of specific sub-modules, while maintaining transparency to permit flexibility in use and application.

Speciation Analysis of Mercury in Aquatic Environment

This review considers methods for mercury speciation with low limits of detection that can be applied to real aquatic environmental samples (waters, sediments, biological tissues). Special attention is given to the necessity of clean sampling procedures and the proper storage of the samples. In this review, different extraction techniques for sediments and biological tissues are considered. The performance of different separation techniques, like liquid chromatography and off‐line and on‐line gas chromatography, are compared for their environmental applications.

Dark Oxidation of Dissolved and Liquid Elemental Mercury in Aquatic Environments

Elemental mercury (Hg0) can be found in liquid or dissolved forms in aquatic systems. Whereas dissolved Hg0 is measured in virtually all aquatic systems, liquid Hg0 droplets are mainly observed at poorly lit sediment/water interfaces of ecosystems with local point sources such as hydro-thermal vents, gold extraction sites, and near industrial facilities. Here, we report that, in the dark, liquid and dissolved forms of Hg behave differently with respect to their oxidation. Liquid Hg0 is rapidly oxidized in oxygenated solution in the presence of chloride. Liquid Hg0 oxidation rates are positively correlated with chloride concentrations and droplet surface area. When liquid Hg is removed from solution, the oxidation stops even though the solution is still saturated with dissolved Hg0. Liquid Hg0 droplets in oxygenated marine or brackish environments should be oxidized and release Hg2+ to solution. In freshwaters or anoxic seawater, liquid Hg will dissolve releasing Hg(aq)0 which, itself, will slowly oxidize.

Temporal variation of total mercury concentrations and burdens in the liver of eelpout Zoarces viviparus from the Forth Estuary, Scotland:implications for mercury biomonitoring

The utility of fishes a s biomonitors for mercury in aquatic environments is widely recognised, with skeletal muscle a s the tissue normally chosen for most monitoring programmes. The liver may also be a suitable candidate tissue for monitoring, as it concentrates many pollutants to higher levels than muscle, and is closely involved with processes of metal dynamics, storage, and detoxification. Little consideration has been given previously to the validation of the use of liver for mercury biomonitoring, with regard to quantifying natural temporal vanation. This study considered such variation in the eelpout Zoarces viviparusL., a resident estuarine fish species collected from a subtidal site near a formerly major industrial mercury discharge in the Forth Estuary, eastern Scotland Llver and skeletal muscle mercury concentrations, liver weight, and body size variables were measured for 196 individual eelpout in seven 3-month periods. Liver Somatic Index (LSI) was significantly hlgher, and liver mercury concentrations significantly lower, in the summer than In other seasons. Llver mercury burden (the mass of liver mercury per fish), in contrast, showed only llmited sign~ficant seasonal variation relative to body size, implying that the observed seasonal variation of liver mercury concentratlon (by around a factor of 3 between summer and winter) results largely from the dilution of simllar burdens by a seasonally growing and shrinking liver. Such natural seasonal variation may confound the use of the muscle/liver mercury concentration ratio, which has been proposed as evldence of fish migrat~on between waters with different levels of mercury contamination. These results also suggest that, as variation in liver mercury concentrations is closely related to seasonal vanation in LSI, liver t~s sue may not be a reliable monitor for mercury in temperate species of marine fishes with seasonally fluctuating l ~ v e r size.

Regional trends in mercury distribution across the Great Lakes states, north central USA

CONCENTRATIONS of mercury in the environment are increasing as a result of human activities, notably fossil-fuel burning and incineration of municipal wastes. Increasing levels of mercury in aquatic environments and consequently in fish populations are recognized as a public-health problem1,2. Enhanced mercury concentrations in lake sediments relative to pre-industrial values have also been attributed to anthropogenic pollution. It is generally assumed that atmospheric mercury deposition is dominated by global-scale processes, consequently being regionally uniform. Here, to the contrary, we report a significant gradient in concentrations and total amounts of mercury in organic litter and surface mineral soil along a transect of forested sites across the north central United States from northwestern Minnesota to eastern Michigan. This gradient is accompanied by parallel changes in wet sulphate deposition and human activity along the transect, suggesting that the regional variation in mercury content is due to deposition of anthropogenic mercury, most probably in particulate form.

Water hyacinth ( Eichhornia crassipes) to biomonitor genotoxicity of low levels of mercury in aquatic environment

The mitotic cell-cycle duration of root meristematic cells of Eichhornia crassipes as determined by the colchicine labelling method was approximately 24 h at 30 ± 1°C. In one experiment the intact root meristems of E. crassipes were subjected to 1 h acute exposure to water contaminated with maleic hydrazide (MH), 56 ppm, or methyl mercuric chloride (MMC1), 0.1–0.5 ppm, followed by recovery in tap water for 4–48 h. In a second experiment the roots were subjected to 96 h exposure to water contaminated with MH, 56 ppm, or MMCl, 0.0001–0.1 ppm. In both experiments the cytological end-point measured was the frequency of cells with micronuclei (MNC). In the first experiment, while in the MH-exposed root meristems the frequency of MNC was significant at 40 h of recovery, MMCl induced significant MNC at 12, 20, 24, 40, and 40 h of recovery depending on the concentration. In the second experiment both test chemicals induced MNC which was concentration-dependent in case of MMCl. The highest ineffective concentration tested (HICT) and lowest effective concentration tested (LECT) for MMC determined in this experiment were 0.0005 ppm and 0.001 ppm, respectively. The present work provides evidence that E. crassipes could be a promising in situ environmental biomonitoring assay system.