The Baihua Reservoir (Guizhou Province, Southwest China) has a history of mercury contamination associated with past acetic acid production activities at the Guizhou Organic Chemical Plant (GOCP). ...Soil and plant samples collected from riparian zones were analyzed for total Hg (THg) and methylmercury (MeHg) using cold vapor atomic fluorescence spectroscopy. The concentrations of THg and MeHg in soil samples were in the range of 109–371 ng g−1 and 0.32–1.80 ng g−1, respectively. Soils in the riparian zones close to the pollution source (the GOCP) presented higher Hg contamination, with relatively light Hg contamination in remote areas. This suggests a decreasing trend of THg concentrations along the riparian zones, with higher concentrations closer to the pollution source. Significant correlations were found between MeHg and soil organic matter (n = 24, p = 0.01). THg concentrations varied 11.3–161 ng g−1 in aboveground areas and 11.3–193 ng g−1 in underground areas. MeHg concentrations ranged from 0.23 to 1.06 ng g−1 in aboveground areas to 0.13–1.51 ng g−1 in the below ground areas. The vegetation studied showed different concentrations of THg and MeHg and can be considered to be impacted by Hg contamination. Different concentrations of total and methyl mercury were found among the different plant species. The high Hg concentrations in soils and vegetation suggests that the ability of Hg to bioaccumulate in riparian plants is affected by plant physiological characteristics and soil mercury concentrations. Although the bioaccumulation factors (BCFs) of the studied plants were low, their transfer factors (TFs) were >1. Our findings suggest that vegetation exhibiting TFs for THg >1 have the potential for phytoextraction in Hg-impacted riparian zones.
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•THg, MeHg concentrations were measured in riparian plants from Hg-impacted reservoir.•THg concentrations decrease along riparian zones due to the pollution from GOCP.•Hg level in riparian plants is affected by physiological features, soil Hg level.•TFs for THg >1 have the potential for phytoextraction in Hg-impacted riparian zones.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Mercury (Hg) is a global pollutant and poses a worldwide concern due to its high toxicity. Guizhou province is recognized as a heavily Hg-polluted area in China due to both the special geochemical ...background and human activities. Here an integrated overview of current knowledge on the behavior of Hg in environments, as well as human health risk with respect to Hg contaminations in Guizhou was presented. Two key anthropogenic Hg emission sources in Guizhou were coal combustion and metals smelting, which dominantly contributed to the high levels of Hg in local ecosystems and high fluxes of Hg deposition. The annual Hg emission from anthropogenic sources ranged between 22.6 and 55.5 t, which was about 6.3–10.3% of current total Hg emissions in China. Meanwhile, Hg Hg-enriched soil in the province serves an important natural Hg emission source to the ambient air. The local environment of Hg mining and zinc smelting areas are seriously contaminated with Hg. It is demonstrated that rice growing in Hg Hg-contaminated soil can accumulate methylmercury (MeHg) to a level to pose health threat to local inhabitants whose staple food is rice. Local inhabitants in Hg mining areas are exposed to Hg through inhalation of Hg vapor and consumption of rice with high level of MeHg. Rice intake is indeed the main MeHg exposure pathway to local inhabitants in Hg mining areas in Guizhou, which is contrary to the general point of view that fish and fish products are the main pathway of MeHg exposure to humans.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Rice paddy plantation is the dominant agricultural land use throughout Asia. Rice paddy fields have been identified as important sites for methylmercury (MeHg) production in the terrestrial ecosystem ...and a primary pathway of MeHg exposure to humans in mercury (Hg) mining areas. We compared the source and distribution of Hg species in different compartments of the rice paddy during a complete rice-growing season at two different typical Hg-contaminated mining sites in Guizhou province, China: an abandoned site with a high Hg concentration in soil but a low concentration in the atmosphere and a current-day artisanal site with a low concentration in soil but a high concentration in the atmosphere. Our results showed that the flux of new Hg to the ecosystem from irrigation and atmospheric deposition was insignificant relative to the pool of old Hg in soil; the dominant source of MeHg to paddy soil is in situ methylation of inorganic Hg (IHg). Elevated MeHg concentrations and the high proportion of Hg as MeHg in paddy water and the surface soil layer at the artisanal site demonstrated active Hg methylation at this site only. We propose that the in situ production of MeHg in paddy water and surface soil is dependent on elevated Hg in the atmosphere and the consequential deposition of new Hg into a low-pH anoxic geochemical system. The absence of depth-dependent variability in the MeHg concentration in soil cores collected from the abandoned Hg mining site, consistent with the low concentration of Hg in the atmosphere and high pH of the paddy water and irrigation water, suggested that net production of MeHg at this site was limited. We propose that the concentration of Hg in ambient air is an indicator for the risk of MeHg accumulation in paddy rice.
Background: Fish consumption is considered the primary pathway of methylmercury (MeHg) exposure for most people in the world. However, in the inland regions of China, most of the residents eat little ...fish, but they live in areas where a significant amount of mercury (Hg) is present in the environment. Objectives: We assessed concentrations of total Hg and MeHg in samples of water, air, agricultural products, and other exposure media to determine the main exposure pathway of Hg in populations in inland China. Methods: We selected Guizhou Province for our study because it is highly contaminated with Hg and therefore is representative of other Hg-contaminated areas in China. We selected four study locations in Guizhou Province: three that represent typical environments with severe Hg pollution due to Hg mining and smelting (Wanshan), traditional zinc smelting (recently closed; Weining), and heavy coal-based industry (Qingzhen), and a village in a remote nature reserve (Leigong). Results: The probable daily intake (PDI) of MeHg for an adult population based on 60 kg body weight (bw) was considerably higher in Wanshan than in the other three locations. With an average PDI of 0.096 μg/kg bw/day (range, 0.015—0.45 μg/kg bw/day), approximately 34% of the inhabitants in Wanshan exceeded the reference dose of 0.1 μg/kg bw/day established by the U.S. Environmental Protection Agency. The PDI of MeHg for residents in the three other locations were all well below 0.1 μg/kg bw/day (averages from 0.017 to 0.023 μg/kg bw/day, with a maximum of 0.095 μg/kg bw/day). In all four areas, rice consumption accounted for 94—96% of the PDI of MeHg. Conclusion: We found that rice consumption is by far the most important MeHg exposure route; however, most of the residents (except those in Hg-mining areas) have low PDIs of MeHg.
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BFBNIB, DOBA, IZUM, KILJ, NMLJ, NUK, OILJ, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK, VSZLJ
Recent studies have shown that rice consumption can be an important pathway of methylmercury (MeHg) exposure to humans in Hg mining areas and also in certain inland areas of Southwestern China. The ...seed of rice has the highest ability to accumulate MeHg compared to other tissues. The main objective of this study was to investigate the process of (MeHg) accumulation in rice seed (Oryza sativa L.) by monitoring MeHg levels in specific tissues of rice plants experiencing various levels of Hg multisource pollution during a full rice growing season. Four groups of experimental plantations were utilized, distributed among a rural artisanal Hg production site and a regional background control site. Our results suggest that the newly deposited Hg is more readily transformed to MeHg and accumulated in rice plants than Hg forms with an extended residence time in soil, and soil is the potential source of MeHg in the tissues of rice plants. MeHg in soil was first absorbed by roots and then translocated to the above-ground parts (leaf and stalk). During the full rice growing season only a very small amount of MeHg was retained in the root section. In the premature plant, the majority of MeHg is located in the leaf and stalk; however, most of this MeHg was transferred to seed during the ripening period.
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IJS, KILJ, NUK, PNG, UL, UM
China is the largest rice producer and consumer in the world, and mercury (Hg) levels, particularly methylmercury (MeHg), in rice and health exposure risks are public concerns. Total Hg (THg) and ...MeHg levels in 767 (domestic = 709 and abroad = 58) Chinese commercial rice were investigated to evaluate Hg pollution level, dietary exposures and risks of IHg and MeHg. The mean rice THg and MeHg levels were 3.97 ± 2.33 μg/kg and 1.37 ± 1.18 μg/kg, respectively. The highest daily intake of MeHg and IHg were obtained in younger groups, accounted for 6% of the reference dose-0.1 μg/kg bw/day for MeHg, 0.3% of the provisional tolerance week intake-0.571 μg/kg bw/day for IHg. Residents in Central China and Southern China meet the highest rice Hg exposure, which were more than 7 times of those in Northwest China. Lower concentrations than earlier studies were observed along the implementations of strict policies since 2007. This may indicate that a declining temporal trend of Hg in Chinese grown rice and associated exposures could be obtained with the implementations of strict policies. Though there exist Hg pollution in commercial rice, Hg levels in Chinese commercial rice is generally safe compared with Hg polluted sites. Populations dwelling in China have relatively a quite low and safe MeHg and IHg exposure via the intake of commercial rice. Strict policies contributed to the decrease in THg and MeHg levels in Chinese-grown rice. More attention should be paid to younger groups.
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•We carried a nationalwide survey of MeHg in Chinese commercial rice.•Hg in rice from Chinese markets is at a safe level.•Rice IHg and MeHg exposures in different Chinese age-gender groups were assessed.•Commercial rice intake doesn’t pose non-carcinogenic risk of MeHg to Chinese.•A declining trend of Hg in Chinese grown rice can be observed in last decade.
Chinese residents have relatively a quite low and decreased MeHg and IHg exposure via rice consumption.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
Cultivation of paddy rice for human consumption is a dominant agricultural activity throughout Asia. High levels of mercury (Hg) in rice grain pose a potential threat to human health, although the ...extent of risk is dependent on the chemical speciation of Hg inside the grain. We have investigated the speciation and localization of Hg in three fractions of rice grain (hull, bran, and white rice) collected from a Hg-contaminated region in China. On a mass basis, the majority of inorganic mercury (IHg) in a rice grain is found in hull and bran. However, the majority of the more toxic species methyl mercury (MeHg) is found in edible white rice. Our data show that during grain processing, most of the IHg (∼78%) is eliminated, but the majority of the MeHg remains in the food product (∼80%). Synchrotron radiation microscopic X-ray fluorescence (SR-μXRF) mapping shows strong localization of Hg at the surface of brown rice grains, corresponding to the pericarp and aleurone layer. We infer that this Hg is predominantly IHg absorbed from the atmosphere. Based on X-ray absorption near-edge spectroscopy (XANES) data we propose that IHg in bran is primarily bound to cysteine, and is associated with phytochelatins. Consequently, IHg is largely immobile and restricted to the outer layers of rice grain. MeHg in bran is primarily bound to cysteine and is associated with proteins. However, this MeHg–cysteine association behaves like a mobile nutrient and is actively transported to the endosperm during seed ripening. Concentration of MeHg–cysteine in white rice has implications for public health. There is growing evidence for Hg contamination of rice throughout Asia due to point and diffuse sources of Hg pollution. The magnitude of the associated risk must be quantified through better understanding of the localization and speciation of mercury in rice. Our work makes an effort to contribute to this understanding.
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IJS, KILJ, NUK, PNG, UL, UM
Rice grain is known to accumulate methylmercury (MeHg) and has been confirmed to be the major pathway of MeHg exposure to residents in mercury (Hg) mining areas in China. Selenium (Se) ...supplementation has been proven to be effective in mitigating the toxicity of Hg. To understand how Se supplementation influences soil Hg speciation, a wide range of Se (0–500 mg/kg) was applied to Hg polluted paddy soils in this study, which decreased MeHg concentration in soil from 2.95 ± 0.36 to 0.69 ± 0.16 μg/kg (or 77%). After Se addition, humic acid state Hg (F4) was transformed into strong-complexed state Hg (F5), indicating that Hg bound up to the non-sulfur functional groups of humic acid (non-RSH) was released and reabsorbed by strong binding Se functional group (F5). As a result, inorganic Hg (IHg) was reduced by >48%, 18%, and 80% in root, stem, and grain, respectively, however, the reduction was not apparent in leaf. Substantial reductions were also found for MeHg in grain and root, but not in stem and leaf. Soil is suggested to be the main source of both MeHg and IHg in rice grain. Such a finding may provide an idea for improving Hg-polluted paddies through controlling soil IHg and MeHg. Further research on the molecular structure of the strong-complexed Hg in F5 should be conducted to elucidate the mechanism of Hg-Se antagonism.
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•Both IHg and MeHg in rice grain primarily originate from soil.•With soil Se addition, humic acid Hg was converted to strong-complexed Hg.•Soil Se addition can remarkably reduce both IHg and MeHg in rice grain.•Controlling soil Hg pollution is the key factor to preventing Hg in rice.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
Understanding mercury (Hg) methylation/demethylation processes and the factors controlling methylmercury (MeHg) production within the rice paddy ecosystem of Hg mining areas is critical to assess the ...risk of MeHg contamination in rice grain. Two typical Hg-contaminated mining sites, a current-day artisanal site (Gouxi) and an abandoned site (Wukeng), were chosen in this study. We qualified the in situ specific methylation/demethylation rate constants in rice paddy soil during a complete rice-growing season. Our results demonstrate that MeHg levels in rice paddy soil were a function of both methylation and demethylation processes and the net methylation potential in the rice paddy soil reflected the measured MeHg production at any time point. Sulfate stimulating the activity of sulfate-reducing bacteria was a potentially important metabolic pathway for Hg methylation in rice paddies. We suggest that bioavailable Hg derived from new atmospheric deposition appears to be the primary factor regulating net MeHg production in rice paddies.
•Methylmercury levels in paddy soil were a function of both methylation and demethylation processes.•Sulfate stimulating the activity of sulfate-reducing bacteria was an important pathway for Hg methylation.•Bioavailable Hg derived from new atmospheric deposition was the primary factor regulating net MeHg production.
Both methylation and demethylation transformed Hg species in paddy fields, and MeHg levels in paddy soil were controlled by both processes.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
Total mercury (THg) and methylmercury (MMHg) were investigated in 259 wild plants belonging to 49 species in 29 families that grew in heavily Hg-contaminated wastelands composed of cinnabar ore mine ...tailings (calcines) in the Wanshan region, southwestern China, the world's third largest Hg mining district. The bioconcentration factors (BCFs) of THg and MMHg from soil to roots (THgroot/THgsoil, MMHgroot/MMHgsoil) were evaluated. The results showed that THg and MMHg in both plants and soils varied widely, with ranges of 0.076–140 μg/g THg and 0.19–87 ng/g MMHg in roots, 0.19–106 μg/g THg and 0.06–31 ng/g MMHg in shoots, and 0.74–1440 μg/g THg and 0.41–820 ng/g MMHg in soil. Among all investigated species, Arthraxon hispidus, Eremochloa ciliaris, Clerodendrum bunge, and Ixeris sonchifolia had significantly elevated concentrations of THg in shoots and/or roots that reached 100 μg/g, whereas Chenopodium glaucum, Corydalisedulis maxim, and Rumex acetosa contained low values below 0.5 μg/g. In addition to the high THg concentrations, the fern E. ciliaris also showed high BCF values for both THg and MMHg exceeding 1.0, suggesting its capability to extract Hg from soils. Considering its dominance and the tolerance identified in the present study, E. ciliaris is suggested to be a practical candidate for phytoextraction, whereas A. hispidus is identified as a potential candidate for phytostabilization of Hg mining-contaminated soils.
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•Total and methylmercury in wild plants grown at wastelands were characterized.•As high as 100 mg/kg total mercury was observed in A. hispidus and E. ciliaris.•Species of E. ciliaris was defined as a hyperaccumulator for Hg phytoremediation.
The species Eremochloa ciliaris and Arthraxon hispidus exhibited elevated Hg concentrations in shoots and roots, respectively, and can be considered candidates for phytoremediation of contaminated soils.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
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