Patterns of Bacterial Diversity Along a Long-Term Mercury-Contaminated Gradient in the Paddy Soils

Mercury (Hg) pollution is usually regarded as an environmental stress in reducing microbial diversity and altering bacterial community structure. However, these results were based on relatively short-term studies, which might obscure the real response of microbial species to Hg contamination. Here, we analysed the bacterial abundance and community composition in paddy soils that have been potentially contaminated by Hg for more than 600 years. Expectedly, the soil Hg pollution significantly influenced the bacterial community structure. However, the bacterial abundance was significantly correlated with the soil organic matter content rather than the total Hg (THg) concentration. The bacterial alpha diversity increased at relatively low levels of THg and methylmercury (MeHg) and subsequently approached a plateau above 4.86 mg kg^?1 THg or 18.62 ng g^?1 MeHg, respectively. Contrasting with the general prediction of decreasing diversity along Hg stress, our results seem to be consistent with the intermediate disturbance hypotheses with the peak biological diversity under intermediate disturbance or stress. This result was partly supported by the inconsistent response of bacterial species to Hg stress. For instance, the relative abundance of Nitrospirae decreased, while that of Gemmatimonadetes increased significantly along the increasing soil THg and MeHg concentrations. In addition, the content of SO₄ ^2?, THg, MeHg and soil depth were the four main factors influencing bacterial community structures based on the canonical correspondence analysis (CCA). Overall, our findings provide novel insight into the distribution patterns of bacterial community along the long-term Hg-contaminated gradient in paddy soils.     

Bioaccumulation and Trophic Transfer of Mercury and Selenium in African Sub-Tropical Fluvial Reservoirs Food Webs (Burkina Faso)

The bioaccumulation and biomagnification of mercury (Hg) and selenium (Se) were investigated in sub-tropical freshwater food webs from Burkina Faso, West Africa, a region where very few ecosystem studies on contaminants have been performed. During the 2010 rainy season, samples of water, sediment, fish, zooplankton, and mollusks were collected from three water reservoirs and analysed for total Hg (THg), methylmercury (MeHg), and total Se (TSe). Ratios of δ¹³C and δ¹⁵N were measured to determine food web structures and patterns of contaminant accumulation and transfer to fish. Food chain lengths (FCLs) were calculated using mean δ¹⁵N of all primary consumer taxa collected as the site-specific baseline. We report relatively low concentrations of THg and TSe in most fish. We also found in all studied reservoirs short food chain lengths, ranging from 3.3 to 3.7, with most fish relying on a mixture of pelagic and littoral sources for their diet. Mercury was biomagnified in fish food webs with an enrichment factor ranging from 2.9 to 6.5 for THg and from 2.9 to 6.6 for MeHg. However, there was no evidence of selenium biomagnification in these food webs. An inverse relationship was observed between adjusted δ¹⁵N and log-transformed Se:Hg ratios, indicating that Se has a lesser protective effect in top predators, which are also the most contaminated animals with respect to MeHg. Trophic position, carbon source, and fish total length were the factors best explaining Hg concentration in fish. In a broader comparison of our study sites with literature data for other African lakes, the THg biomagnification rate was positively correlated with FCL. We conclude that these reservoir systems from tropical Western Africa have low Hg biomagnification associated with short food chains. This finding may partly explain low concentrations of Hg commonly reported in fish from this area.     

Xylem sap as a pathway for total mercury and methylmercury transport from soils to tree canopy in the boreal forest

Conifer needles are an important link in the cycling of Total Mercury (THg) and Methylmercury (MeHg) in the boreal ecosystem due to the high THg and MeHg concentrations in litterfall. Translocation within the tree of Hg from soils to the crown canopy has been assumed to be a minor source of the Hg in litterfall. This paper, however, is the first to present direct observations of THg/MeHg transport from the soil via xylem sap. Xylem sap concentrations of THg and MeHg were measured in sap drained from different levels along the boles of freshly cut 100 year old Norway spruce (Picea abies) and Scots pine (Pinus sylvestris). The trees came from a mixed stand growing on podzolized till soils at the Svartberget Forest Research Station in N. Sweden. Soil solution concentrations of THg and MeHg at different levels in the soil profile were measured for comparison.Concentrations of THg in xylem sap ranged from 10–15 ng L^-1 in both the Scots pine and Norway spruce. Concentrations of MeHg varied from 0.03 ng L^-1to 0.16 ng L^-1, with higher values in Scots pine than Norway spruce. If these concentrations are representative of the transport from soils to needles in xylem sap at this site, then only 3% of the MeHg in litterfall (0.12 mg ha^-1 yr^-1) and 11% of the THg (26 mg ha^-1 yr^-1) can originate via this pathway. The upward transport via xylem sap is larger relative to the open field inputs (84% of THg and 17% of MeHg). Comparison of soil solution and xylem sap THg/MeHg suggested some degree of THg exclusion during water uptake in Scots pine and Norway spruce, but MeHg exclusion only in Norway spruce.     

Mercury and Selenium in Stranded Indo-Pacific Humpback Dolphins and Implications for Their Trophic Transfer in Food Chains

As top predators in the Pearl River Estuary (PRE) of China, Indo-Pacific humpback dolphins (Sousa chinensis) are bioindicators for examining regional trends of environmental contaminants in the PRE. We examined samples from stranded S. chinensis in the PRE, collected since 2004, to study the distribution and fate of total mercury (THg), methylmercury (MeHg) and selenium (Se) in the major tissues, in individuals at different ages and their prey fishes from the PRE. This study also investigated the potential protective effects of Se against the toxicities of accumulated THg. Dolphin livers contained the highest concentrations of THg (32.34±58.98 µg g⁻¹ dw) and Se (15.16±3.66 µg g⁻¹ dw), which were significantly different from those found in kidneys and muscles, whereas the highest residue of MeHg (1.02±1.11 µg g⁻¹ dw) was found in dolphin muscles. Concentrations of both THg and MeHg in the liver, kidney and muscle of dolphins showed a significantly positive correlation with age. The biomagnification factors (BMFs) of inorganic mercury (Hg_inorg) in dolphin livers (350×) and MeHg in muscles (18.7×) through the prey fishes were the highest among all three dolphin tissues, whereas the BMFs of Se were much lower in all dolphin tissues. The lower proportion of MeHg in THg and higher Se/THg ratios in tissues were demonstrated. Our studies suggested that S. chinensis might have the potential to detoxify Hg via the demethylation of MeHg and the formation of tiemannite (HgSe) in the liver and kidney. The lower threshold of hepatic THg concentrations for the equimolar accumulation of Se and Hg in S. chinensis suggests that this species has a greater sensitivity to THg concentrations than is found in striped dolphins and Dall’s porpoises.     

Methylmercury and Total Mercury in Eels, <Emphasis Type="Italic">Anguilla anguilla</Emphasis>, from Lakes in Northeastern Poland: Health Risk Assessment

In the aquatic environment, mercury is readily methylated into its most toxic form of methylmercury. In this form, it enters the aquatic food chain and its concentrations increase in subsequent links, which decreases the quality of fish meat and poses risks to consumer health. Concentrations of methylmercury (MeHg) and total mercury (THg) were determined in the muscle tissues of 64 eel specimens measuring from 59 to 95 cm in length as functions of specimen size and weight. Risks posed to consumers by eel from different length classes were also assessed. The mean concentration of THg in all of the eel examined was 0.179 mg kg^?1, but the range was from 0.028 to 0.487 mg kg^?1. The mean concentration of MeHg was 0.147 mg kg^?1, and the range was also wide from 0.023 to 0.454 mg kg^?1. Accumulated MeHg and THg increased with eel body length. The percentage share of MeHg in THg also changed with specimen length, and there was a positive correlation between the concentrations of MeHg and THg. Risk assessment was performed based on the doses of THg and MeHg ingested with fish for several specimen length classes. Consuming the meat of eel measuring 80 cm in length increased the estimated weekly intake (EWI) of THg and MeHg twofold in comparison to that from specimens 60 cm in length and fourfold in specimens exceeding 90 cm in length. The percentage shares of the EWI in the tolerable weekly intake and the target hazard quotient coefficient also increased proportionally. Generally, concentrations of MeHg and THg in eel are below current limits and pose no risk to consumer health as long as the consumption of larger specimens is avoided.     

中亚热带常绿阔叶林凋落物分解过程中汞的动态变化及迁移机理

森林凋落物对于汞在林地土壤的生物地球化学循环中起到重要作用,为研究森林凋落物分解过程中汞的迁移转化特征,以重庆四面山风景名胜区典型林分(常绿阔叶林)作为研究对象。于2014年3月—2015年3月连续监测典型林分凋落物中各形态汞浓度和有机质变化量,同时监测周围土壤中汞浓度变化。结果表明:四面山典型林分凋落物分解过程中汞浓度整体上升,总汞浓度(初始浓度:78 ng/g)的增幅最高达53%,甲基汞浓度(初始浓度:0.32 ng/g)最高增幅达138%;在春季和夏季,水溶态和酸溶态两种活性态汞含量分别增加了851%和96%,在分解前期和末期,凋落物汞的中惰性汞比例最高,占比达75%。土壤腐殖质层中总汞和甲基汞浓度比较稳定。凋落物中活性态汞通过雨水淋洗进入土壤与有机质络合并发生甲基化/去甲基化过程,通过地表径流、地下径流进入水体。凋落物中C含量减少了22%,N含量增加了15%,总汞浓度与C/N比呈负相关,与N含量呈正相关。凋落物中微生物C、N含量整体增加,与汞浓度峰值同步,且夏季含量显著高于冬季含量(P0.05),说明微生物与凋落物固定汞和汞的甲基化过程密切相关。     

Forestry Influence by Stump Harvest and Site Preparation on Methylmercury, Total Mercury and Other Stream Water Chemistry Parameters Across a Boreal Landscape

Forestry has been reported to cause elevated mercury (Hg) concentrations in runoff water. However, the degree to which forestry operations influence Hg in runoff varies among sites. A synoptic study, covering 54 catchments distributed all over Sweden, subjected to either stump harvest (SH), site preparation (SP) or no treatment (Ref), was undertaken to reveal the degree of forestry impact and causes of eventual variation. All streams were sampled twice, in autumn 2009 and summer 2010. There were no significant differences in total mercury (THg) and methylmercury (MeHg) concentrations between the three treatments in either 2009 or 2010. However, when pooling the treated catchments (that is, SH and SP) and taking catchment properties such as latitude into account, the treatment had a significant influence on the THg and MeHg concentrations. Although the treatment effect on THg and MeHg did not differ between SH and SP, the study did reveal significant forestry effects on potassium (K) and total nitrogen (TN) that were greater in the SH catchments and lower in the SP catchments. Partial least square (PLS) regressions indicated that organic matter was the most important variable influencing both the THg and MeHg concentrations. There were no significant differences between the treatment groups when comparing the ratios of THg/total organic carbon (TOC) and MeHg/TOC, suggesting that the high concentrations of THg and MeHg observed at some of the treated catchments are associated with increased concentrations of TOC rather than new methylation or increased mobilization caused by factors other than TOC.     

Effect of urban sewage treatment on total and methyl mercury concentrations in effluents

The purpose of this study was to investigate the effect of sewage treatment on total mercury (THg) and methylmercury (MeHg) concentrations in domestic effluents and the contribution of urban sewage treatment facilities to THg and MeHg in rivers. We determined the concentrations of THg and MeHg in unfiltered samples of untreated and treated domestic sewage from the three treatment facilities and receiving river water within the City of Winnipeg. The concentrations of THg in the Red and Assiniboine rivers ranged from 3–31 ng/L. THg was related positively to suspended sediment concentrations in the rivers. The concentrations of MeHg in these rivers were usually 0.2–0.3 ng/L. THg concentrations in raw sewage varied widely, from 2–150 ng/L. Treatment removed an average of 88% of this mercury. MeHg concentrations in raw sewage were 0.5–4.3 ng/L, however, after treatment at two treatment facilities, MeHg was greatly reduced, usually to 0.1–0.4 ng/L. Most treated sewage, therefore, had MeHg concentrations that were similar to levels in the receiving rivers and the effect of discharged effluent was usually a change of about 2% or less on concentrations in the rivers. However, one of the facilities (the West End plant) was discharging higher concentrations of MeHg, up to 2 ng/L, causing calculated increases of up to 11% in the concentration of MeHg in the Assiniboine River.     

Effects of environment and genotype on mercury and methylmercury accumulation in rice (<Emphasis Type="Italic">Oryza sativa</Emphasis> L.)

Background and aims

Rice grains contaminated by mercury (Hg) and methylmercury (MeHg) pose risks to human health. This study evaluated the relative importance of genotype, environment and genotype-environment interactions on the accumulation of total Hg (THg) and MeHg in brown rice.

Methods

A pot trial with four rice genotypes and 10 Hg-contaminated paddy soils was conducted under greenhouse conditions. The effects of genotype, environment and genotype-environment interactions on brown rice THg and MeHg accumulation were assessed by an Additive Main Effects and Multiplicative Interaction (AMMI) model.

Results

THg and MeHg concentrations in brown rice ranged from 20.5 to 75.5 μg kg^?1 and 2.24 to 54.7 μg kg^?1, respectively. The AMMI model indicated that genotype explained 41.1 and 19.6%, environment described 40.6 and 55.8%, and the genotype-environment interaction explained 11.9 and 20.0% of the variation in brown rice THg and MeHg levels, respectively. Brown rice THg positively correlated with water-soluble Hg and total potassium, but negatively correlated with total sulphur, iron, total organic carbon and nickel in soils. Brown rice MeHg negatively correlated with soil pH and selenium.

Conclusion

THg accumulation in brown rice was mainly affected by both genotype and environment, whereas MeHg accumulation was largely determined by environment.

     

Dietary Exposure of the Red-Crowned Crane (Grus japonensis) to Total and Methyl Mercury in Zhalong Wetland,Northeastern China

To determine the dietary exposure of the migratory red-crowned crane to mercury (Hg), this study analyzed the concentrations of total mercury (T-Hg) and methyl mercury (MeHg) in its prey, i.e., reeds and three aquatic animal families (Perccottus glenni Dybowski, Cybister japonicus Sharp, and Viviparidae) in northeastern China. Results indicated that the Hg concentration in Zhalong Wetland was elevated through the food chain, and the prey of the red-crowned crane contained measurable levels of T-Hg and MeHg. In prey tissues, MeHg was the main form of the Hg element and accounted for 61 % of total Hg concentration in Viviparidae, 58 % in C. japonicus Sharp, and 85 % in P. glenni Dybowski. The highest T-Hg and MeHg concentrations ranged from 1.66 to 3.89 ppm and from 1.12 to 2.67 ppm, respectively, and they were detected in the feathers of the red-crowned cranes. The lowest T-Hg concentration was determined in the excretions of wild red-crowned cranes at 0.21 ppm; furthermore, the content of MeHg was below the detection limit. In Zhalong Wetland, the level of dietary exposure of the population of red-crowned cranes to Hg is below the threshold of Hg toxicity. Moreover, eggshells are suitable indicators of Hg risk levels to the red-crowned crane.     

An examination of current Hg deposition and export in Fenno-Scandian catchments

The input and output flux data of total Hg (THg) and methylmercury (MeHg) from three catchments located in different geographical regions in Sweden and one catchment in southern Finland were compared to elucidate the role of current atmospheric Hg/MeHg deposition with regard to waterborne Hg/MeHg output.There was a negative co-variaton between the open field THg inputs and the ratio of THg output to open field input. The highest ratio (and lowest input) occurring in N. Sweden and S. Finland, while the lowest output ratio (and highest inputs) occurred in southwest Sweden. A much larger variation was found in the ratio of output to open field input for MeHg (14 to 160%). Examinations of MeHg input/output data in relation to catchment charateristics suggest that riparian peat, mires and wet organic soil contributed to the large MeHg output from certain catchments, probably due to in situ production of MeHg. This finding is consistent with other studies which have found that catchment characteristics such as wetland area, flow pathways, seasonal temperature and water flow are important in controlling the output of MeHg. These catchment characteristics govern the fate of the contemporary input of Hg and MeHg as well as the mobilization of the soil pools.     

Effect of Electron Donor to Sulfate Ratio on Mercury Methylation in Floodplain Sediments under Saturated Flow Conditions

A column transport experiment was conducted to examine the release and methylation of Hg using Hg contaminated sediment from the floodplain of the South River near Waynesboro, Virginia. Three input solutions were sequentially introduced into the column. Input 1 was unamended South River water, Input 2 was river water amended with 100 mg L^?1 SO₄ and 3600 mg L^?1 lactate, and Input 3 was river water amended with 500 mg L^?1 SO₄ and 340 mg L^?1 lactate. During the first stage of the experiment (Input 1) the effluent Hg concentration was initially 4 µg L^?1 and peaked at 21 µg L^?1 and after 21 pore volumes stabilized at 13 µg L^?1. During the second stage, at high lactate to SO₄ ratios, elevated concentrations of acetic and propionic acids were detected, indicating that fermentative bacteria were dominant. During the third stage, at high SO₄ to lactate ratios, a decrease in SO₄ and an increase in H₂S concentrations were detected in the column effluent indicating that SO₄ reduction was occurring. Concentrations of methyl Hg (MeHg) in the effluent were variable over the duration of the experiment. During the first phase, concentrations of MeHg remained <3.3 ng L^?1. During the fermentative stage, concentrations of MeHg increased to a maximum value of 32 ng L^?1, and during the sulfate-reducing stage to a maximum value of 266 ng L^?1. When the column was deconstructed both molecular and cultural techniques indicated that sulfate reducing bacteria were most dominant near the influent port. These results indicate that the formation of MeHg in the sediment is not limited by the availability of Hg and that the bacterial community that contributes to mercury methylation can respond quickly to changes in the abundances of electron donors and acceptors.     

Phytoremediation of mercury- and methyl mercury-contaminated sediments by water hyacinth (Eichhornia crassipes)

Phytoremediation has the potential for implementation at mercury- (Hg) and methylHg (MeHg)-contaminated sites. Water hyacinths (Eichhornia crassipes) were investigated for their ability to assimilate Hg and MeHg into plant biomass, in both aquatic and sediment-associated forms, over a 68-day hydroponic study. The suitability of E. crassipes to assimilate both Hg and MeHg was evaluated under differing phosphate (PO4) concentrations, light intensities, and sediment:aqueous phase contamination ratios. Because aquatic rhizospheres have the ability to enhance MeHg formation, the level of MeHg in water, sediment, and water hyacinth was also measured. Hg and MeHg were found to concentrate preferentially in the roots of E. crassipes with little translocation to the shoots or leaves of the plant, a result consistent with studies from similar macrophytes. Sediments were found to be the major sink for Hg as they were able to sequester Hg, making it non-bioavailable for water hyacinth uptake. An optimum PO4 concentration was observed for Hg and MeHg uptake. Increasing light intensity served to enhance the translocation of both Hg and MeHg from roots to shoots. Assimilation of Hg and MeHg into the biomass of water hyacinths represents a potential means for sustainable remediation of contaminated waters and sediments under the appropriate conditions.     

Mercury in blood,hair, and feces from subsistence fish-eating riverines of the Madeira River Basin (Western Amazon)

BackgroundThe Madeira River (Amazon Basin) has been impacted by activities related to artisanal and small-scale gold mining (ASGM), deforestation and burning (for timber, agriculture, and hydroelectric dam projects). All these activities contribute to environmental mercury (Hg) release and cycling into the Amazon ecosystem and thus to changing lifestyles.MethodWe assessed exposure to total and MeHg in two small riverine communities of the Madeira River (Amazon): Lago Puruzinho (LP, n = 26 families) and São Sebastião do Tapurú (SST, n = 31 families). Samples of human hair (n = 137), blood (n = 39), and feces (n = 41) were collected from adults and children (0–15 years of age).ResultsIn women of childbearing age from LP village, the mean blood total-Hg (THg) (45.54 ± 24.76 μg.L⁻¹) and MeHg (10.79 ± 4.36 μg.L⁻¹) concentrations were significantly (p = 0.0024; p < 0.0001, respectively) higher than in women from SST village (THg: 25.32 ± 16.75 μg.L⁻¹; MeHg: 2.32 ± 1.56 μg.L⁻¹) village; the trend in hair-Hg persisted but was statistically significant (p < 0.0145) only for THg (LP, 11.34 ± 5.03 μg. g⁻¹; SST, 7.97 ± 3.51 μg. g⁻¹). In women, the median hair:blood ratio of total Hg was 269. In children, the mean hair THg concentrations were 6.07 ± 3.60 μg. g⁻¹ and 6.47 ± 4.16 μg. g⁻¹ in LP and SST; thus, not significantly different (p = 0.8006). There was a significant association (p < 0.001) between hair-Hg concentrations of mothers and their respective children. The excretion of Hg in feces of women (0.52 μg. g⁻¹ dw) was not significantly different from children (0.49 μg. g⁻¹ dw). The only statistically significant correlation between Hg in feces and in hair was found in children, (n = 16, r_s = 0.38, p = 0.005). Significant relationship was seen between the levels of THg in blood and hair of women from LP and SST. Based on hair-Hg concentrations, fish consumption rate ranged from 94.5 to 212.3 g.day⁻¹.ConclusionWomen and children excrete THg in feces in comparable concentrations. However, the mean fish consumption rate and blood MeHg are higher in the most remote villagers. Mother`s hair-Hg concentration is a good predictor of children’s hair-Hg.     

Total mercury and methylmercury in garfish (Belone belone) of different body weights,sizes, ages,and sexes

BackgroundGarfish, (Belone belone) is a migratory pelagic fish that inhabits the waters of coastal Europe, North Africa, the North Sea, the Mediterranean Sea. Little information about garfish has been disseminated mainly because of its low abundance and its brief occurrence in various water bodies. Data is lacking on mercury compounds, particularly dangerous the toxic organic form of methylmercury (MeHg), which endangers the health of fish and their consumers.MethodsThe research material was garfish caught off the southern Baltic Sea coast in Puck Bay during the spawning period. Total mercury (THg) content was assayed with the cold vapour atomic absorption method in an AMA 254 mercury analyser. The MeHg extraction procedure was based on three-step sequential extraction method: hydrolysis using of hydrochloric acid, extract by toluene, bind the MeHg by L-cysteine.ResultsThe concentrations of THg and MeHg was determined in the muscle of garfish. The highest concentrations of THg (0.210 mg kg-1) and MeHg (0154 mg kg-1) were detected in the longest specimens (80 cm). The THg and MeHg concentrations in garfish muscles increased with specimens length, weight and age, which was confirmed by positive correlations. Differences were also noted depending on sex. Males accumulated more THg and MeHg than did females. The mercury in garfish from the southern Baltic Sea occurred mainly in its organic form MeHg and accounted for 84.7% of the THg.ConclusionSignificant differences were noted in mercury concentrations depends on length, weight, age and sex. Concentration of MeHg in garfish must be done by length class, and fish sex when selecting this fish for contamination studies and risk assessment. The toxic MeHg in garfish tissues did not pose a threat to the health of consumers, as indicated by the low values of EDI, TWI and THQ indices.     

Mercury contamination and stable isotopes reveal variability in foraging ecology of generalist California gulls

Environmental contaminants are a concern for animal health, but contaminant exposure can also be used as a tracer of foraging ecology. In particular, mercury (Hg) concentrations are highly variable among aquatic and terrestrial food webs as a result of habitat- and site-specific biogeochemical processes that produce the bioaccumulative form, methylmercury (MeHg). We used stable isotopes and total Hg (THg) concentrations of a generalist consumer, the California gull (Larus californicus), to examine foraging ecology and illustrate the utility of using Hg contamination as an ecological tracer under certain conditions. We identified four main foraging clusters of gulls during pre-breeding and breeding, using a traditional approach based on light stable isotopes. The foraging cluster with the highest δ¹⁵N and δ³⁴S values in gulls (cluster 4) had mean blood THg concentrations 614% (pre-breeding) and 250% (breeding) higher than gulls with the lowest isotope values (cluster 1). Using a traditional approach of stable-isotope mixing models, we showed that breeding birds with a higher proportion of garbage in their diet (cluster 2: 63–82% garbage) corresponded to lower THg concentrations and lower δ¹⁵N and δ³⁴S values. In contrast, gull clusters with higher THg concentrations, which were more enriched in ¹⁵N and ³⁴S isotopes, consumed a higher proportion of more natural, estuarine prey. δ³⁴S values, which change markedly across the terrestrial to marine habitat gradient, were positively correlated with blood THg concentrations in gulls. The linkage we observed between stable isotopes and THg concentrations suggests that Hg contamination can be used as an additional tool for understanding animal foraging across coastal habitat gradients.     

Role of Organic Carbon Sources and Sulfate in Controlling Net Methylmercury Production in Riverbank Sediments of the South River,VA (USA)

Mercury (Hg) transport and methylmercury (MeHg) production in riverbank sediments are complex processes influenced by site-specific physical and biogeochemical conditions. The South River watershed in VA, USA, contains elevated concentrations of Hg in riverbank and floodplain sediments, which has the potential to methylate. The role of specific organic carbon sources in promoting methylation reactions in natural sediments under dynamic flow conditions is not well understood. Four saturated column experiments were conducted, including a control column, which received South River water as an influent solution, and three columns that received South River water amended with: acetate (5.8 mM); lactate (5.7 mM); and lactate (5.7 mM) with SO₄^2? (10.1 mM). The amendments were selected to promote growth of different microorganisms to gain an understanding of the microbial processes, controlling rates of methylation. The column receiving lactate and SO₄^2? had the highest MeHg concentrations in the effluent and in the pore water near the effluent at 1.8 and 4.9 μg L^?1, respectively. At the cessation of the column experiments, the lactate–sulfate column sediments contained the highest populations of enumerable sulfur-reducing bacteria and the highest solid-phase MeHg at 530 ± 100 ng g^?1 dry wt. from the interval closest to the influent. The results suggest that the form and availability of electron donors and acceptors are primary factors controlling rates of methylation in the South River sediment.     

Metabolic and oxidative impairments in human salivary gland cells line exposed to MeHg

Background/aimThe ingestion of contaminated seafood by MeHg is considered the main route of human exposure, turning the salivary gland one important target organ. The salivary glands play critical roles in maintaining oral health homeostasis, producing saliva that maintains the oral microbiota, initiation of the digestion of macromolecules, and being essential in maintaining the integrity of the adjacent soft tissues and teeth. Thus, this study aimed to investigate the effects of MeHg exposure on human salivary gland cells line.MethodsCells were exposed to 1–6 μM of MeHg for 24 h, and analysis of toxicity was performed. Based on these results, the LC50 was calculated and two concentrations were chosen (0.25 and 2.5 μM MeHg) to evaluate intracellular mercury (Hg) accumulation (THg), metabolic viability and oxidative stress parameters (GSH:GSSG ratio, lipid peroxidation, protein oxidation and DNA damage).ResultsThe results demonstrated accumulation of THg as we increased the MeHg concentrations in the exposure and, the higher the dose, the lower is the cell metabolic response. In addition, the 2.5 μM MeHg concentration also triggered oxidative stress in human salivary gland cells by depleting the antioxidant competence of GSH:GSSG ratio and increasing lipid peroxidation and proteins carbonyl levels, but no damages to DNA integrity.ConclusionIn conclusion, although these two elected doses did not show lethal effects, the highest dose triggered oxidative stress and new questionings about long-term exposure models are raised to investigate furthers cellular damages to human salivary gland cells caused by MeHg exposure to extrapolate in a translational perspective.     

Accelerating recovery of the mercury-contaminated Wabigoon/English River system

Mercury levels (essentially methyl mercury — MeHg) in sportfish in a 250 km section of the Wabigoon-English River system remain seriously elevated as a result if the discharge of approximately 10 tonnes of inorganic Hg from a chlor-alkali plant at Dryden, Ontario, Canada which occurred primarily between 1962 and 1970. The discharges resulted in elevated mercury concentrations in water, sediments and biota. For example, Hg in adult Northern Pike in Clay Lake routinely exceeded 3 µg/g (ppm). Field studies in 1978–1981 suggest that partitioning of inorganic and MeHg between surface sediment, water and suspended particles occurs within days. MeHg levels in water were partitioned with total (essentially inorganic) Hg. Temperature affects both Hg and MeHg levels in water; concentrations fluctuated seasonally by an order of magnitude at some sites. Hg in contaminated surface sediments is almost certainly the primary source of the mercury now entering the water and biota in this contaminated watercourse. Mercury levels in biota decline less dramatically with distance downstream of Dryden than mercury concentrations in sediments. Natural erosion, resuspension and sedimentation processes have helped to reduce the amount of mercury in the active layer at the sediment/water interface and the most effective means of accelerating the recovery of the system will probably involve measures to accelerate these natural processes. Enclosure experiments, regional surveys and geochemical studies all provide evidence that the biological uptake of upstream anthropogenic Hg loadings at any given site would likely be reduced dramatically by the continuous addition of very modest quantities of pristine clay sediment. The quantities contemplated, when resuspended, would result in suspended solids concentrations on the order of 15–25 ppm, a value higher than for most shield waters but well within the range of many other productive watercourses in North America. The ability to mitigate local sources and ameliorate the adverse biological effects of anthropogenic loadings from upstream sources by resuspension of clean clay sediments permits targeting of sites for restoration and opens a wide array of ameliorative options. The authors believe that some of these options would be more effective and less costly than other restoration procedures commonly considered such as dredging and on land disposal of contaminated sediment.The views expressed are those of the authors and do not necessarily reflect the views of the Ontario Ministry of the Environment or the International Joint Commission. No endorsement should be inferred.     

Mercury-selenium relationships in liver of Guiana dolphin: the possible role of kupffer cells in the detoxification process by tiemannite formation

Top marine predators present high mercury concentrations in their tissues as consequence of biomagnification of the most toxic form of this metal, methylmercury (MeHg). The present study concerns mercury accumulation by Guiana dolphins (Sotalia guianensis), highlighting the selenium-mediated methylmercury detoxification process. Liver samples from 19 dolphins incidentally captured within Guanabara Bay (Rio de Janeiro State, Brazil) from 1994 to 2006 were analyzed for total mercury (THg), methylmercury (MeHg), total organic mercury (TOrgHg) and selenium (Se). X-ray microanalyses were also performed. The specimens, including from fetuses to 30-year-old dolphins, comprising 8 females and 11 males, presented high THg (0.53-132 μg/g wet wt.) and Se concentrations (0.17-74.8 μg/g wet wt.). Correlations between THg, MeHg, TOrgHg and Se were verified with age (p<0.05), as well as a high and positive correlation was observed between molar concentrations of Hg and Se (p<0.05). Negative correlations were observed between THg and the percentage of MeHg contribution to THg (p<0.05), which represents a consequence of the selenium-mediated methylmercury detoxification process. Accumulation of Se-Hg amorphous crystals in Kupffer Cells was demonstrated through ultra-structural analysis, which shows that Guiana dolphin is capable of carrying out the demethylation process via mercury selenide formation.