Distribution Of Methylmercury Research Articles

Distribution of mercury and methylmercury in ice-water-sediments in lakes during the freezing period under the influence of ice cover

The presence of lake ice cover alters the subglacial water environment, thereby influencing the migration and transformation of mercury (Hg) and methylmercury (MeHg) within the ice-water-sediment media of lakes. This study investigated the occurrence characteristics of mercury and methylmercury in various environmental compartments within lakes located at high latitudes in cold regions during the freezing period. To this end, Wuliangsuhai Lake, the largest freshwater lake situated at 40°N in China, was selected as the study site. The contents of mercury and methylmercury in lake ice were determined for the first time. The percentage of methylmercury (MeHg%) and ice-water partition coefficient were analyzed. The pollution situation and health risk were evaluated by single factor pollution index. The results show that the ice body and water body of Wuliangsuhai are not polluted by mercury and methylmercury, but some sampling points in the sediment are slightly polluted. The mercury content in sediment is negatively correlated with the ice thickness, and the methylmercury content in water is positively correlated with the methylmercury content in sediment, but negatively correlated with the ice thickness. The migration ability of methylmercury in ice-water system is stronger than that of mercury. The MeHg% of water in ice period is higher than that in non-freezing period, which is different from other lakes without ice sheet. The results show that in the dynamic equilibrium of methylation and demethylation in the high-latitude lake water, the methylation is higher in the ice period than in the non-freezing period due to the influence of light intensity, while the mercury in the non-freezing period is more susceptible to the demethylation.

Impacts of oyster farms on sediment-associated mercury and methylmercury concentrations and health risks in an estuarine, mangrove forest, Zhanjiang Bay, China

Estuarine sediments serve as significant reservoirs for mercury (Hg) and methylmercury(MeHg), which can also interconvert in the external environment. The release of Hg in response to human activities raises concerns about its potential ecological and human health effects. Sediment samples were collected in December 2021 from four locations (sites), and Hg cycling by measuring the concentrations of, and controls on, the spatial distribution of total Hg (THg) and methylmercury (MeHg) in high-tidal zone (HTZ) and mid-tidal zone (MTZ) sediments of a mangrove forest (MF) and oyster farm (OF) was examined in northwestern Zhanjiang Bay, including simultaneous determination of sediment particle size, oxidation-reduction potential (Eh), pH, total organic carbon (TOC), sulfide concentration (S2-), and sulfate reducing bacteria (SRB). The research results indicated that concentrations of both THg and MeHg ranged between 20.0–104.0 ng/g and 0.011–0.277 ng/g in the sediments, respectively. The highest methylation potentials within the MF and OF were in sediments located approximately 10–15 cm below the surface. MeHg in the HTZ of the OF was likely derived from exogenous inputs as Hg methylation appears limited, and the formation of MeHg depended not only on the amount of inorganic mercury available for methylation in SRB, but also on the TOC, pH, Eh and S2- content in the sediment. A risk assessment of MeHg during the anthropogenic disturbance of this estuaries conducted on individuals eating oysters demonstrated that health risks are low.

Methylmercury and mercury in Mediterranean mussels (Mytilus galloprovincialis) from Turkish coast: Dietary exposure prediction

The spatial distribution of total mercury (HgT) and methylmercury (MeHg) in Mediterranean mussels (Mytilus galloprovincialis) sampled at 23 different stations along Türkiye's Black Sea, the Marmara, and Aegean Sea coasts were investigated in this study. HgT and MeHg were determined using a direct mercury analyzer and ranged 1.10–130.70 μg/kg and 0.22–37.90 μg/kg dry weight, respectively. HgT and MeHg have been determined to have a substantial positive correlation (r2 = 0.94). According to average consumption and portion sizes, the weekly intake (EWI) for MeHg was less than the 1.6 μg/kg/week limits set by the FAO/WHO Joint Committee of Experts on Food Additives (JECFA) for both pediatric and adult consumers. The Target Risk Coefficients (THQ) were calculated to explain the potential long-term exposure scenarios. Our data showed that the excessive consumption of mussels from areas with high MeHg concentrations might pose a risk only for pediatric consumers. The determination of suitable sites for healthy-sustainable mussel production as well as the prevention of collecting mussels from illegal and polluted fields and placing them on the market, should be considered in the context of consumer health awareness.

Distribution and Release of Mercury Regulated by the Decomposition of a Pioneer Habitat-Adapted Plant in the Water-Level-Fluctuating Zone of the Three Gorges Reservoir.

Pioneer habitat-adapted bermudagrass is prevalent in the water-level-fluctuating zone of the Three Gorges Reservoir area. This study was performed to explore the response characteristics of dissolved organic matter (DOM) qualities to bermudagrass decomposition and their regulation in the distribution and release of mercury (Hg) and methylmercury (MeHg) in the soil-water system. Compared to the control, the bermudagrass decomposition resulted in a great increase in the protein-like components in the water in the initial stages (p < 0.01), but it also greatly reduced the humification degree of water DOM (p < 0.01). However, it accelerated the consumption of protein-like components, the humification rate, and the synthesis of humic-like DOM in the water over time. This changing pattern of the DOM qualities resulted in an initial elevation and a subsequent great decrease in the dissolved Hg and MeHg concentrations in the pore water, which ultimately reduced their release levels into the overlying water by 26.50% and 54.42%, respectively, compared to the control. Our results indicate the potential inhibitory effects of short-term bermudagrass decomposition caused by flooding and how decomposition affects the release of total Hg and MeHg by shaping the DOM qualities, and they have implications for similar aquatic systems in which herbaceous plants are frequently decomposed after submergence.

Geochemical controls on the distribution of total mercury and methylmercury in sediments and porewater from the Yangtze River Estuary to the East China Sea

A comprehensive investigation was conducted to explore the distributions of total mercury (THg) and methylmercury (MeHg) in sediments and porewater along a typical transect from the Yangtze River Estuary (YRE) to the East China Sea (ECS) open shelf. THg concentrations in the surface sediments exhibited large variations across sites, higher in the estuary mixing region, especially within the turbidity maximum zone (TMZ). The spatial and vertical distributions (0–20 cm) of THg in sediments were highly controlled by sediment grain size and total organic carbon (TOC), due to the strong binding between Hg and fine-grained sediments that enriched with organic matter. In contrast, MeHg concentrations in surface sediments were higher in the estuary mixing region and the ECS open shelf than in the river channel, with remarkably higher MeHg/THg ratios in sediments and porewater at the open shelf sites, identified as the regional hotspots of the net in situ MeHg production. Considering the large gradients of physiochemical properties of sediments, porewater and the overlying water, the results of this study suggested that the higher net Hg methylation potential in the open shelf region was largely attributed to the lower acid volatile sulfide, lower TOC and higher salinity, which facilitated the partitioning of inorganic Hg into porewater that highly bioavailable for Hg-methylation bacteria. Moreover, the estimated diffusive fluxes of MeHg at the sediment-water interface were positive at all the tested sites, and pronouncedly higher within the TMZ (driven by the higher THg loading and higher porosity) that requires special attention.

Riverine input of suspended particulate matter controls distribution, partitioning and transport of mercury and methylmercury in the Yellow River Estuary

Riverine mercury (Hg) is the largest global source of Hg in coastal oceans. The Yellow River delivers the majority of Hg to the semi-enclosed Bohai Sea, where Hg contamination adversely affects the surrounding heavily populated provinces in northern China. Mercury distribution patterns in the river-estuary interacting area provides essential information to understand the riverine Hg transport and biogeochemical cycling of Hg in the estuary. Analyzing the spatial distributions of total- (THg) and methyl-Hg (MeHg) in the lower end of Yellow River (∼105 km) and adjacent estuary, we found the dominant role of suspended particulate matter (SPM) in Hg transport, with 99.1% and 86.3% of THg and MeHg being in particulate phase. The SPM dynamics, such as transport, retention, sorting and sedimentation, governs Hg transport with water flow and particle-water partition of Hg. While THg decreased along the water flow to the river mouth with the settlement of particulate THg (about 27.5% onto the riverbed and the rest entering the sea), MeHg and particulate MeHg increased by 110% and 117%, respectively. This study highlights the distinct patterns in THg and MeHg distribution and transport and suggests potential Hg methylation and external MeHg input in the river-estuary mixed zone.

Spatial distribution of total mercury and methylmercury in the sediment of a tropical coastal environment subjected to heavy urban inputs

Jurujuba Cove is located in Guanabara Bay (adjacent to highly populated city of Rio de Janeiro, Brazil), which receives diffuse sources of contaminants along with two main freshwater inputs (the Cachoeira and Icaraí rivers), and hosts mussel farms. The main goal of this work was to evaluate the total mercury (THg) and methylmercury (MeHg) concentrations distributions in the sediments of the cove and their associations with physical and chemical parameters, thereby assessing their geochemical behavior. Twenty samples of surface sediments were collected and characterized for grain size, pH, redox potential, organic carbon, total phosphorus, THg and MeHg. Spatial distribution maps were produced for each parameter and a principal components analysis was carried out, to assess THg and MeHg behavior and their relationships with other parameters. The principal components analysis showed that grain size functions as the main diluting agent. The highest THg concentrations were observed in the mussel-farm area (656.1 ng g−1), and were related to fine grain size and elevated organic carbon values. High MeHg concentrations also occurred in the center of the cove, probably favored by high organic carbon content (low-energy environment). Total phosphorus concentrations indicate that Cachoeira River is a possible source of sewage, but little mercury seems to come from it. The results showed that although total mercury concentrations are elevated, with exception of a few locations, small methylmercury convertion rates were recorded in the sediments.

Distribution of Mercury and Methylmercury in Farmland Soils Affected by Manganese Mining and Smelting Activities.

Manganese (Mn)-related activities would affect the mercury (Hg) cycling in farmlands, whereas this was not well understood. Here, one of the largest Mn ores in China was selected to study the effects of Mn-related activities on the accumulation and distribution of total Hg (THg) and methylmercury (MeHg) in farmland soils. The soil THg concentrations in the mining area were 0.56 ± 0.45, 0.56 ± 0.45, 0.53 ± 0.44, and 0.50 ± 0.46 mg kg−1 in the 0–10, 10–20, 20–30, and 30–40 cm layers, respectively, while they were increased to 0.75 ± 0.75, 0.72 ± 0.60, 0.62 ± 0.46, and 0.52 ± 0.38 mg kg−1 in the smelting area. Similarly, the soil MeHg concentrations in the smelting area were also elevated by 1.04–1.34 times as compared to those in the mining area. Concentrations of THg (0.59 ± 0.50 mg kg−1) and MeHg (0.64 ± 0.82 μg kg−1) in soils were higher than the regional background value but lower than in vicinal Hg-mining areas, while they were largely elevated at the intersection of two rivers in the smelting area. Significant positive Mn-THg relationship (p < 0.01) and negative Mn-MeHg relationship (p < 0.01) favored the conclusion that soil Mn could promote Hg accumulation while inhibiting MeHg production. Approximately 70% of soil Hg was distributed in the residual phase, and the environmental hazard was not elevated according to a geochemical model. Overall, mining and smelting activities of Mn ores have resulted in obvious and distinct effects on the accumulation and methylation of Hg in farmland soils, but the environmental hazards are currently manageable.

Mercury concentrations in tuna blood and muscle mirror seawater methylmercury in the Western and Central Pacific Ocean

Understanding the relationship between mercury in seafood and the distribution of oceanic methylmercury is key to understand human mercury exposure. Here, we determined mercury concentrations in muscle and blood of bigeye and yellowfin tunas from the Western and Central Pacific. Results showed similar latitudinal patterns in tuna blood and muscle, indicating that both tissues are good candidates for mercury monitoring. Complementary tuna species analyses indicated species- and tissue- specific mercury patterns, highlighting differences in physiologic processes of mercury uptake and accumulation associated with tuna vertical habitat. Tuna mercury content was correlated to ambient seawater methylmercury concentrations, with blood being enriched at a higher rate than muscle with increasing habitat depth. The consideration of a significant uptake of dissolved methylmercury from seawater in tuna, in addition to assimilation from food, might be interesting to test in models to represent the spatiotemporal evolutions of mercury in tuna under different mercury emission scenarios.

Microbial mercury methylation potential in a large-scale municipal solid waste landfill, China

Landfills harbor ideal conditions for microbial mercury methylation. However, the levels and distribution of mercury (Hg) and methylmercury (MeHg), potential microbial Hg methylation, and their linkage within landfills are largely unknown. In the present study, total mercury (THg), MeHg, the Hg methylation gene (hgcA) and mer operon were quantified in 30 waste samples from different depths (0–30 m) at 5 locations within a large-scale landfill in China. The average concentrations of THg and MeHg in the solid waste samples were 1422.91 ng/g and 3.15 ng/g, respectively. THg (up to 14405.29 ng/g) and MeHg (up to 10.42 ng/g) have high concentrations in the middle part (10–15 m) along the depth profiles. The concentration of THg was strongly positively (both p < 0.05) correlated with the MeHg concentration and the relative abundance of hgcA, indicating that the THg concentration can play an important role in microbial Hg methylation. The hgcA genes were detected in most samples and mer operon were detected in all samples. Combined hgcA qPCR and metagenomics data showed that Archaea Methanofollis may mainly account for Hg methylation within landfills. These findings provide fundamental knowledge on Hg cycles in landfills.

Distribution and accumulation of mercury in pot-grown African rice cultivars (Oryza glaberrima Steud. and Oryza sativa L.) determined via LA-ICP-MS.

There is limited information concerning the distribution of mercury in rice, particularly in African rice. The objective was to compare the distribution of total mercury (THg) and methylmercury (MeHg) in African rice (Oryza glaberrima Steud.) and Asian rice (O. sativa L.). It is hypothesized that increased mineral accumulation and greater stress tolerance in O. glaberrima will affect the uptake and distribution of THg and MeHg, compared to O. sativa. Rice varieties from the Republic of Mali, including O. glaberrima (n =1) and O. sativa (n = 2), were cultivated in a greenhouse, in mercury-spiked soil (50 mg/kg) (n =3 replicates/variety). THg and MeHg concentrations were analyzed in the grain (brown rice), and the THg distribution was analyzed using laser ablation inductively coupled-plasma mass spectrometry (LA-ICP-MS). THg and MeHg concentrations did not differ between O. glaberrima and O. sativa grain. However, in both O. sativa varieties, THg was highly concentrated in the scutellum, which surrounds the embryo and is removed during polishing. Conversely, in O. glaberrima grain, THg was widely distributed throughout the endosperm, the edible portion of the grain. Differences in the THg distribution in O. glaberrima grain, compared to O. sativa, may elevate the risk of mercury exposure through ingestion of polished rice. The novelty of this study includes the investigation of a less-studied rice species (O. glaberrima), the use of a highly sensitive elemental imaging technique (LA-ICP-MS), and its finding of a different grain THg distribution in O. glaberrima than has been observed in O. sativa.

Distribution of mercury and methylmercury in river water and sediment of typical manganese mining area

Manganese (Mn) ores contain substantial concentrations of mercury (Hg), and mining and smelting of Mn ores can bring Hg into the surrounding aquatic environment through atmospheric deposition, leaching of electrolytic Mn residue and Mn gangue dump. However, limited is known that how these processes influence the environmental behaviors of Hg in waterbody. Therefore, the seasonal distribution and existing form of Hg in water and sediment in one Mn ore area in Xiushan County, Chongqing were investigated. Our results showed that the mean Hg and methylmercury (MeHg) concentrations in water (n=35) were 5.8 ± 4.6 ng/L and 0.22 ± 0.14 ng/L, respectively. The mean Hg concentrations in retained riverbed and fluvial bank sediment (n=35) were 0.74 ± 0.26 mg/kg and 0.63 ± 0.27 mg/kg, respectively (the mean MeHg concentrations were 0.64 ± 0.40 µg/kg and 0.51 ± 0.30 µg/kg, respectively). It indicated that the mining and smelting of Mn ores were the main sources of anthropogenic Hg, and Mn may inhibit Hg methylation in rivers in Mn ore areas. Mercury in the bound to iron/ Mn (Fe/Mn) oxides of low crystallinity fraction (Hg-OX) accounted for 4.01% and 5.25% of the total Hg concentrations in the retained riverbed and fluvial bank sediment, respectively. The amount of Hg bound to Fe/Mn oxides in sediment increased significantly due to the manganese mining activities in the investigated area. Therefore, it could be hypothesized that high Hg concentrations in river sediment in Mn mining areas are closely related to high Mn concentration in sediment.

Subcellular Distribution of Dietary Methyl-Mercury in Gammarus fossarum and Its Impact on the Amphipod Proteome.

The transfer of methyl-Hg (MeHg) from food is central for its effects in aquatic animals, but we still lack knowledge concerning its impact on invertebrate primary consumers. In aquatic environments, cell walls of plants are particularly recalcitrant to degradation and as such remain available as a food source for long periods. Here, the impact at the proteomic level of dietary MeHg in Gammarus fossarum was established and linked to subcellular distribution of Hg. Individuals of G. fossarum were fed with MeHg in cell wall or intracellular compartments of Elodea nuttallii. Hg concentrations in subcellular fractions were 2 to 6 times higher in animals fed with cell wall than intracellular compartments. At the higher concentrations tested, the proportion of Hg in metal-sensitive fraction increased from 30.0 ± 6.1 to 41.0 ± 5.7% for individuals fed with intracellular compartment, while biologically detoxified metal fraction increased from 30.0 ± 6.1 to 50.0 ± 2.8% when fed with cell wall compartment. Data suggested that several thresholds of proteomic response are triggered by increased bioaccumulation in each subcellular fraction in correlation with Hg exclusively bound to the metal-sensitive fraction, while the increase of biologically detoxified metal likely had a cost for fitness. Proteomics analysis supported that the different binding sites and speciation in shoots subsequently resulted in different fate and cellular toxicity pathways to consumers. Our data confirmed that Hg bound in cell walls of plants can be assimilated by G. fossarum, which is consistent with its feeding strategy, hence pointing cell walls as a significant source for Hg transfers and toxicity in primary consumers. The high accumulation of Hg in macrophytes makes them a risk for food web transfer in shallow ecosystems. The present results allowed gaining new insights into the effects and uptake mechanisms of MeHg in aquatic primary consumers.

The effect of beaver dams on organic carbon, nutrients and methyl mercury distribution in impounded waterbodies

The European beaver Castor fiber is well‐known as an ecosystem engineer that greatly affects landscape structure, biodiversity as well as physical and chemical properties of surface water bodies. Beaver ponds alter surface water bodies by raising water elevation, decreasing flow velocity and altering the morphology of streams or drainage ditches, which can reduce the concentrations of organic carbon (OC) and nutrients (N, P). Recent studies indicated that mercury transforms into hazardous and neurotoxic methylmercury (MeHg) in beaver impoundments by biological processes in anaerobic conditions.However, the knowledge about nutrients and MeHg levels in impounded forest waterbodies is scarce in Lithuania. We aimed to ascertain the alteration in concentrations and stocks of OC, nutrients and MeHg in water and sediments from upstream and downstream, as well as within beaver dams and ponds during the growing seasons of 2016–2018. Results showed higher concentrations of dissolved organic carbon (DOC) and nutrients (P and N) in upstream water samples compared to those of downstream from beaver dams. Meanwhile, in sediments mean stocks of OC, P and N were the highest in the middle part of the ponds and in beaver dams. Moreover, the concentrations and stocks of MeHg in sediments were higher in beaver dams than in any other parts of beaver impoundments (upstream, mid‐pond, pond periphery and downstream). We conclude that dam bottom sediments were rich in OC, N and P, and at the same time, contained toxic MeHg. Therefore, beaver dams could act as a trickle filter by improving water quality, in our case, DOC, N and P leaching, from riparian forests and soils, but may also act as hotspots of mercury methylation.

Ecosystem-Scale Modeling and Field Observations of Sulfate and Methylmercury Distributions in the Florida Everglades: Responses to Reductions in Sulfate Loading

The Florida Everglades has one of the most severe methylmercury (MeHg) contamination issues in the USA, resulting from factors including high rates of atmospheric mercury (Hg) deposition and sulfate inputs from agricultural lands. Sulfate loading stimulates microbial sulfate reduction and production of toxic and bioaccumulative MeHg. Controls on regional Hg emissions have been successful in reducing Hg deposition and MeHg production in wetlands in other areas, but this has not been the case for the Everglades as the Hg deposited here appears to come from unknown global sources of emissions. We posit that reductions in sulfate loading to the Florida Everglades can be an effective alternative approach used to reduce MeHg production. This study tested this hypothesis (1) by evaluating temporal trends in MeHg concentrations in response to a reduction in sulfate loading at a site in central Water Conservation Area (WCA) 3 and (2) using ecosystem-scale models to predict the effects of reductions in sulfate loading on sulfate concentrations in surface water and MeHg Risk. At the WCA site, we report a decline in sulfate concentrations (from about 9 mg/L in the late 1990s to levels of 33% in sulfate loading will significantly benefit the Everglades by reducing MeHg Risk.

Distribution of total mercury and methylmercury and their controlling factors in the East China Sea

Mercury (Hg) is among contaminants of public concern due to its prevalent existence, high toxicity, and bioaccumulation through food chains. Elevated Hg has been detected in seafood from the East China Sea (ECS), which is one of the largest marginal seas and an important fishing region in the northwestern Pacific Ocean. However, there is still a lack of knowledge on the distribution of Hg species and their controlling factors in the ECS water column, thus preventing the understanding of Hg cycling and the assessment of Hg risks in the ECS. In this study, two cruises were conducted in October 2014 and June 2015 in order to investigate the distribution of total Hg (THg) and methylmercury (MeHg) and their controlling factors in the ECS. The concentrations of THg and MeHg were determined to be 4.2 ± 2.8 ng/L (THg) and 0.25 ± 0.13 ng/L (MeHg) in water from the ECS. The level of Hg in the ECS occupied the higher rank among the marginal seas, thus indicating significant Hg contamination in this system. Both the THg and MeHg presented complicated spatial distribution patterns in the ECS, with high concentration areas located in both the nearshore and offshore areas. Statistical analyses suggest that temperature (T) and Hg in sediment may be the controlling factors for THg distribution, while dissolved organic matter (DOM), T, and MeHg in the sediment may be the controlling factors for MeHg distribution in the seawater of the ECS. The relative importance of these environmental factors in Hg distribution depends on the water depth. T-salinity (S) diagram analyses showed that water mass mixing may also play an important role in controlling THg and MeHg distribution in the coastal ECS.

Mercury species in the nests and bodies of soil-feeding termites, Silvestritermes spp. (Termitidae, Syntermitinae), in French Guiana

Mercury pollution is currently a major public health concern, given the adverse effects of mercury on wildlife and humans. Soil plays an essential role in speciation of mercury and its global cycling, while being a habitat for a wide range of terrestrial fauna. Soil fauna, primarily soil-feeding taxa that are in intimate contact with soil pollutants are key contributors in the cycling of soil mercury and might provide relevant indications about soil pollution. We studied the enrichment of various mercury species in the nests and bodies of soil-feeding termites Silvestritermes spp. in French Guiana. Soil-feeding termites are the only social insects using soil as both shelter and food and are major decomposers of organic matter in neotropical forests. Nests of S. minutus were depleted in total and mobile mercury compared to nearby soil. In contrast, they were enriched 17 times in methylmercury. The highest concentrations of methylmercury were found in body of both studied termite species, with mean bioconcentration factors of 58 for S. minutus and 179 for S. holmgreni relative to the soil. The assessment of the body distribution of methylmercury in S. minutus showed concentrations of 221 ng g−1 for the guts and even higher for the gut-free carcasses (683 ng g−1), suggesting that methylmercury is not confined to the gut where it was likely produced, but rather stored in various tissues. This enrichment in the most toxic form of Hg in termites may be of concern on termite predators and the higher levels in the food chain that may be endangered through prey-to-predator transfers and bioaccumulation. Soil-feeding termites appear to be promising candidates as bio-indicators of mercury pollution in soils of neotropical rainforest ecosystems.

The distribution of methylmercury in estuary and harbor sediments.

Methylmercury (MeHg) presents high toxicity to humans and can be accumulated to organisms via the food chains. In aquatic environments, MeHg is mainly formed by microorganism using the bioavailable inorganic mercury in sediment. In this study, a total of 120 surface sediments from 20 sites in the Kaohsiung Harbor were collected quarterly in the period from July 2016 to October 2017 and analyzed for total mercury (THg), bioavailable inorganic mercury (BIHg), MeHg, and several geochemical parameters. The concentrations of THg, BIHg, and MeHg in sediment were 455-5108, 7.0-1021, and 0.84-24.1 μg/kg dw, respectively. Results indicated that the percentage of MeHg to THg (MeHg ratio) in most sediment (85%) is <1.2%. Correlation analysis showed that MeHg in sediment was mainly controlled by BIHg (r = 0.759, p < 0.01), while the concentration of BIHg in sediment was mainly related to TOC (r = 0. 480, p < 0.01) and THg (r = 0.435, p < 0.01). The relationship between total bioavailable inorganic mercury (containing BIHg and the bioavailable inorganic mercury used in the synthesis of MeHg) and MeHg concentration in the sediments that collected from the estuary, harbor channel, and the entrance was established by a Michaelis-Menten model to predict the maximum value of MeHg. The efficiency of Hg methylation in the sediments of Kaohsiung Harbor is significantly affected by the total bioavailable inorganic mercury and the related environmental factors. In addition, changes in environmental conditions caused by local seasonality should also be an important factor to consider when assessing the efficiency of Hg methylation.

Total and methyl mercury distribution in water, sediment, plankton and fish along the Tapajós River basin in the Brazilian Amazon

Mercury (Hg) is known as one of the major contaminants in the Amazon. The Tapajós River basin, in the Brazilian Amazon, has diverse anthropogenic activities which increase Hg concentrations in the aquatic ecosystem. Moreover, high concentrations of Hg are naturally found in this basin. Distribution of total (THg) and methyl (MeHg) mercury were assessed in unfiltered water (n = 47), suspended particulate matter (SPM, n = 30), superficial sediment (BS, n = 29), plankton (n = 28) and fishes (n = 129) from the Tapajós River basin. Suspended particles were the main carrier of Hg in the water column and sediment. Increased erosion, prompted by anthropic activities, led to higher Hg concentrations in water from the most impacted areas. Hg is transported mainly in particulate matter; thus, anthropic disturbances influence Hg concentrations downstream. Limnological parameters such as organic matter content influenced MeHg concentrations in water, plankton and sediment of the Tapajós basin. Hg methylation in total plankton was more efficient in lakes (13-66%) than in Tapajós River main channel (2-14%). Biotic and abiotic factors interact in a complex way in the aquatic ecosystem, making Hg concentrations to vary in food web. Gold mining and deforestation probably increase Hg levels in the Tapajós basin. Thus, in addition to Hg monitoring, prevention and remediation efforts should be focused on soil and sediment erosion control.

Distribution of mercury and methylmercury in surface water and surface sediment of river, irrigation canal, reservoir, and wetland in Taiwan.

In Taiwan, because of the co-use of some irrigation and drainage canals, a portion of industrial wastewater was directly discharged into irrigation canals or even flowed into rivers or wetlands, causing the heavy metal pollution in waters and sediments. Mercury (Hg) contamination in rivers, irrigation canals, and wetlands has been found in Taiwan, but a thorough investigation on the distribution of Hg and methylmercury (MeHg) in these waters and sediments, which may be present in a greater level with elevating total Hg (THg) concentration and markedly impact human health, is still lacking. In this study, surface waters and surface sediments were sampled from five major rivers, two irrigation canals, two reservoirs, and one wetland in Taiwan, and their THg and MeHg concentrations were quantified. Additionally, statistical analysis was carried out to understand the relationship between sediment properties and MeHg levels. The results showed that irrigation canal sediments were relatively more polluted by Hg and the THg concentrations of some sampling points exceeded the upper limit (i.e., 0.87mgkg-1) of sediment quality index (SQI) for THg promulgated by Taiwan Environmental Protection Administration, which may be attributed to the co-use of irrigation and drainage canals. Furthermore, the MeHg concentration in irrigation canal sediments was the highest; rivers came in second followed by wetlands. In addition, the Siangshan Wetland was analyzed to have the greatest THg and MeHg concentrations in its surface water. Linear regression analysis also indicated that total organic carbon and clay content substantially affected the MeHg production in sediments.