Mercury pollution in two typical areas in Guizhou province, China and its neurotoxic effects in the brains of rats fed with local polluted rice

Assessing mercury pollution at a primary ore site with both ancient and industrial mining and smelting activities

The Minamata Convention on Mercury has mandated a renewed global effort to tackle Hg pollution. The present study evaluates Hg pollution at a primary Hg production site exploited since the Qin Dynasty (200s BC), with intensive industrial scale production over the past four decades. This single location accounts for over 95% total Hg production in China in recent years. To assess the environmental risk and effectiveness of recently implemented control measures, we collected 90 soil samples, 60 plant tissue samples, 47 sediment samples, and 47 river water samples from the site and its vicinity. A site-specific conceptual site model was established based on the sources, migration transformation pathways of Hg pollutant and its exposure scenarios. The maximum soil Hg concentration reached 10,451 mg kg-1, posing a high health and ecological risk. Vegetable and crop Hg concentrations outside the site reached 0.23 mg kg-1 in rice grains and 4.24 mg kg-1 in green onion. The highest health risk, with a hazard quotient of 130.66, was observed in the Ore Storage Site, which reduced to 17.14 when Hg bioavailability was considered. Risk control measures implemented in recent years included a stormwater collection system and capping of the tailing pond area with clean imported soil. These measures were generally successful; however, Hg in the tailings were found to be contaminating the imported surficial soil due to rainfall saturation and upward migration, suggesting a need for long-term post remedial site monitoring and maintenance. We also found that mining and smelting activities have contaminated a 6 km stretch of a nearby river, with sediment Hg concentrations reaching 2819 mg kg-1, and water column concentrations reaching 193.21 ng L-1. The sediment and water concentrations are highly correlated (R2 = 0.78), suggesting that, with risk control measures in place, a reservoir of Hg in polluted river sediment is now driving pollution in the water column. This work demonstrates that primary Hg mining has caused widespread and serious soil and water pollution. Risk control measures can reduce human health and ecological risks, but robust monitoring and maintenance are required for remediation to be effective in the long-term.

Mercury bioaccumulation and its toxic effects in rats fed with methylmercury polluted rice

Recent evidence indicated that methylmercury (MeHg) contaminated rice can be a significant source of MeHg human exposure, but the health implications are not known. The objective of this study was to study the kinetics, speciation, and effects of MeHg contaminated rice using a rat model. Five groups of adult Sprague-Dawley rats (n=10 in each group) were fed control rice, low (10ng/g MeHg) and high (25ng/g MeHg) MeHg contaminated rice. Two groups of the positive control were fed control rice spiked with the same levels of MeHgCl. Short-term exposure to low level of spiked MeHgCl stimulated the growth of male rats while long-term exposure to spiked MeHgCl inhibited the growth in female rats. There was no temporal variation of total mercury (THg) concentrations in the rat fecal samples from each group, and the THg concentrations significantly correlated with the inorganic Hg concentrations in the feeding rice. There were significant differences in the accumulation of THg and MeHg among different groups and different organs. THg and MeHg concentrations in the kidney were the highest among the organs examined. The blood and brain had high percentages of THg as MeHg, which indicates that MeHg can easily pass through the blood-brain barrier and has a high affinity for brain tissue. Exposure to rice containing 25ng/g MeHg decreased antioxidant function and damaged the nervous system in rats, but no significant effects were found in the group fed with rice containing 10ng/g MeHg. MeHgCys in rice is less toxic than spiked MeHgCl to rats. The toxicity of MeHg both decided by its concentration and speciation.

A Portable Smart-Phone Readout Device for the Detection of Mercury Contamination Based on an Aptamer-Assay Nanosensor

The detection of environmental mercury (Hg) contamination requires complex and expensive instruments and professional technicians. We present a simple, sensitive, and portable Hg²⁺ detection system based on a smartphone and colorimetric aptamer nanosensor. A smartphone equipped with a light meter app was used to detect, record, and process signals from a smartphone-based microwell reader (MR S-phone), which is composed of a simple light source and a miniaturized assay platform. The colorimetric readout of the aptamer nanosensor is based on a specific interaction between the selected aptamer and Hg²⁺, which leads to a color change in the reaction solution due to an aggregation of gold nanoparticles (AuNPs). The MR S-phone-based AuNPs-aptamer colorimetric sensor system could reliably detect Hg²⁺ in both tap water and Pearl River water samples and produced a linear colorimetric readout of Hg²⁺ concentration in the range of 1 ng/mL-32 ng/mL with a correlation of 0.991, and a limit of detection (LOD) of 0.28 ng/mL for Hg²⁺. The detection could be quickly completed in only 20 min. Our novel mercury detection assay is simple, rapid, and sensitive, and it provides new strategies for the on-site detection of mercury contamination in any environment.

Mercury levels and estimated total daily intakes for children and adults from an electronic waste recycling area in Taizhou, China: Key role of rice and fish consumption

In order to assess the potential health risks of Hg pollution, total mercury (T-Hg) and methyl mercury (MeHg) concentrations were determined in air, dust, surface soil, crops, poultry, fish and human hair samples from an electronic waste (e-waste) recycling area in Taizhou, China. High concentrations of T-Hg and MeHg were found in these multiple matrices, and the mean concentration was 30.7 ng/m(3) of T-Hg for atmosphere samples, 3.1 μg/g of T-Hg for soil, 37.6 μg/g of T-Hg for dust, 20.3 ng/g of MeHg for rice and 178.1 ng/g of MeHg for fish, suggesting that the e-waste recycling facility was a significant source of Hg. The inorganic Hg (I-Hg) levels (0.84 μg/g) in hair samples of e-waste workers were much higher than that in the reference samples. Pearson's correlation coefficients showed that strong positive correlations (p<0.01) between hair I-Hg and time staying in industrial area (r=0.81) and between MeHg and fish consumption frequency (r=0.91), imply that workers were mainly exposed to Hg vapor through long-time inhalation of contaminated air and dust, while other population mainly exposed to MeHg through high-frequency fish consumption. The estimated daily intakes of Hg showed that dietary intake was the major Hg exposure source, and Hg intakes from rice and fish were significantly higher than from any other foods. The estimated total daily intakes (TDIs) of MeHg for both children (696.8 ng/(kg·day)) and adults (381.3 ng/(kg·day)) greatly exceeded the dietary reference dose (RfD) of 230 ng/(kg·day), implying greater health risk for humans from Hg exposures around e-waste recycling facilities.

Assessment of neurotoxic effects and brain region distribution in rat offspring prenatally co-exposed to low doses of BDE-99 and methylmercury

Exposure to polybrominated diphenyl ether (PDBE) and methylmercury (MeHg) can occur simultaneously as both contaminants are found in the same food sources, especially fish, seafood, marine mammals and milk. The aim of this study was to assess the effects of exposure to low levels of MeHg (2.0 μg mL(-1) in drinking water) and BDE-99 (0.2 mg kg(-1) d(-1)) from gestational day 6 to postnatal day (PND) 21, alone and in combination, on neurobehavioral development and redox responses in offspring. The present study demonstrated an interaction due to co-exposure with low doses of MeHg and BDE-99 enhanced developmental neurotoxic effects. These effects were manifested as the delayed appearance of negative geotaxis reflexes, impaired motor coordination, and induction of oxidative stress in the cerebellum. In particular, the cerebellum may be a sensitive target for combined MeHg and BDE-99 toxicity. The neurotoxicity of low dose MeHg was exacerbated by the presence of low dose of BDE-99. It is concluded that prenatal co-exposure to MeHg and BDE-99 causes oxidative stress in the cerebellum of offspring by altering the activity of different antioxidant enzymes and producing free radicals. Hg retention was not affected by co-exposure to BDE-99. However, MeHg co-exposure seemed to increase BDE-99 concentrations in selected brain regions in pups compared to pups exposed to BDE-99 only. These results showed that the adverse effects following prenatal co-exposure to MeHg and BDE-99 were associated with tissue concentrations very close to the current human body burden of this persistent bioaccumulative compound.

Neurobehavioral effects, c-Fos/Jun expression and tissue distribution in rat offspring prenatally co-exposed to MeHg and PFOA: PFOA impairs Hg retention

Exposure to methylmercury (MeHg) and perfluorooctanoic acid (PFOA) can occur simultaneously as both contaminants are found in the same food sources, especially fish, seafood, marine mammals and milk. The aim of this study was to assess the effects of exposure to MeHg (10 μg mL(-1) in drinking water) and PFOA (10 μg mL(-1) in drinking water) from gestational day 1 to postnatal day (PND) 21, alone and in combination, on neurobehavioral development and the expression of c-Fos/Jun in different brain regions in the offspring. Our findings showed that exposure to MeHg alone, and exposure to MeHg combined with PFOA significantly induced cliff avoidance reflexes and negative geotaxis reflexes. And these effects appeared to be greater following exposure to MeHg alone. MeHg and/or PFOA exposure did not significantly impair motor coordination functions, or cause significant changes in c-Fos expression in the hippocampus and cerebellum, and spatial learning tests were similar to those in the controls, thus it was impossible to determine whether combined exposure to MeHg and PFOA had any additional effects on both hippocampus and cerebellum regions. However, a significant increase in the frequency of line crossing was observed in rats treated with MeHg or PFOA alone, and there were no significant differences between the MeHg+PFOA-treated group and the controls, suggesting that PFOA was antagonistic to MeHg toxicity in the locomotor activity test. Co-exposure to MeHg and PFOA decreased all tissue Hg concentrations in pups compared to the group exposed to MeHg only, suggesting that PFOA impaired Hg retention in different tissues.

Characterization of residues from dismantled imported wastes

Residues from the imported wastes dismantling process create a great burden on the ambient environment. To develop appropriate strategies for the disposal of such residues, their characteristics were studied through background value analysis and toxicity leaching tests. Our results showed that the heavy metals concentrations in residues were high, particularly those of Cu (7180 mg kg(-1)), Zn (2783 mg kg(-1)), and Pb (1954 mg kg(-1)). Toxicity leaching tests revealed a high metal releasing risk of such residues if they are disposed of in a landfill. However, the residues of imported wastes were also found to have some intrinsic metal recycling value.

Accumulation of mercury, selenium and PCBs in domestic duck brain, liver and egg from a contaminated area with an investigation of their redox responses

PCBs and methylmercury (MeHg) are two of the most ubiquitous contaminants in the Qingzhen (QZ) area of Guizhou province. The estimated tolerable daily intakes (TDIs) of total mercury (T-Hg), MeHg, PCBs and Se from contaminated rice, eggs and fish by Chinese people in QZ showed that both MeHg and PCBs exceeded the corresponding safety limits. Pearson's correlation analyses of mercury and Se in all duck tissues showed that there were high correlations with T-Hg or MeHg and Se in QZ samples. However, the molar ratio between T-Hg and Se in brain tissues was close to 1, suggesting that Se is antagonistic to mercury toxicity only in brain tissues. Biochemical analyses showed that both superoxide dismutase and glutathione peroxidase increased in the brain, whereas in the liver and egg these enzymes decreased. However, lipid peroxidation and H2O2 generation in liver and egg tissues showed contrary responses, where significant increases in these tissues were seen relative to controls. Mercury and PCBs co-accumulation in liver and egg tissues gave rise to large numbers of free radicals as well as aggravated alkyl free radicals, superoxide radical and nitric oxide, thereby resulting in oxidative stress in these tissues. It can be concluded that an adaptive response of the redox defense system is present in brain tissues, as opposed to a general break down of the redox defense system in liver and egg. The results obtained in this study will provide basic information on exposure and risk assessment in local residents.

Remediation of mercury contaminated sites - A review

Environmental contamination caused by mercury is a serious problem worldwide. Coal combustion, mercury and gold mining activities and industrial activities have led to an increase in the mercury concentration in soil. The objective of this paper is to present an up-to-date understanding of the available techniques for the remediation of soil contaminated with mercury through considering: mercury contamination in soil, mercury speciation in soil; mercury toxicity to humans, plants and microorganisms, and remediation options. This paper describes the commonly employed and emerging techniques for mercury remediation, namely: stabilization/solidification (S/S), immobilization, vitrification, thermal desorption, nanotechnology, soil washing, electro-remediation, phytostabilization, phytoextraction and phytovolatilization.

Synthesis of current data for Hg in areas of geologic resource extraction contamination and aquatic systems in China

China has become the largest contributor of anthropogenic atmospheric mercury (Hg) in the world owing to its fast growing economy and the largest of populations. Over the last two decades, Hg has become of increasing environmental concern in China and much has been published on its distribution, transportation, methylation, and bioaccumulation in aquatic systems and areas of geologic resource extraction contaminated sites, such as coal-fired power plants, non-ferrous smelters, Hg mining and retorting sites, Au amalgam, landfills, chemical plants, etc.. Environmental compartments, like soil, water, air, and crop from areas of geologic resource extraction contamination, especially from Hg mining regions, exhibit elevated values of total-Hg and MMHg. Risk assessments indicate that the consumption of rice, which has a high bioaccumulation of MMHg, has become the dominant pathway of MMHg exposure of inhabitants living in Hg mining areas. Low concentrations less than 5ngl(-1) in total-Hg can be observed in rivers from remote areas, however, high concentrations that reached 1600ngl(-1) in total-Hg can be found in rivers from industrial and urban areas. The studies of hydropower reservoirs of southwest China indicated the old reservoirs act as net sinks for total-Hg and net sources of MMHg, while newly established ones act as net sinks for both total-Hg and MMHg, which is in sharp contrast to the evolution of biomethylation in reservoirs established in the boreal belt of North America and Eurasia. Fish from those reservoirs have relatively low levels of total-Hg, which do not exceed the maximum total-Hg limit of 0.5mgkg(-1) recommended by WHO. Currently, however, there is still a large data gap regarding Hg even in the areas mentioned above in China, which results in poor understanding of its environmental biogeochemistry. Moreover, for a better understanding of human and environmental health effects caused by the fast growing economy, long-term Hg monitoring campaigns are urgently needed.

Neurotoxicological effects of low-dose methylmercury and mercuric chloride in developing offspring mice

Mercury is a well-known toxic metal and potently induces severe neurotoxicological effects, especially in infants and children. The purpose of this study was to explore the underlying mechanisms of neurotoxic effects of mercurial compounds on the different stages of developing mice. Low-doses (the probability of human exposure in mercury-contaminated areas) of methylmercury (MeHg) (M, 0.02mg/kg/day) and mercury chloride (HgCl(2)) (H, 0.5mg/kg/day) were administered to mice of the following groups: (1) treatment with distilled water for 7 consecutive weeks after weaning (control-vehicle (CV)); exposure to mercurial compounds at different stages; (2) for 7 consecutive weeks after weaning (control-MeHg (CM) and control-HgCl(2) (CH)); (3) only during perinatal and weaning stages (MeHg-vehicle (MV) and HgCl-vehicle (HV)); and (4) in all experimental stages (MeHg-MeHg (MM) and HgCl(2)-HgCl(2) (HH)). Results revealed the neurobehavioral defects (increased locomotor activities, motor equilibrium impairment, and auditory dysfunction) that correlated with increasing Hg accumulation in CM and CH groups. However, it revealed a decrease and an increase in locomotor activities in MV and HV groups, respectively; these became more severe in MM and HH groups than in MV and HV groups. Motor equilibrium performance in MV and HV groups remained normal, while that in MM and HH groups was decreased. The most severe auditory defects (altered auditory brainstem response, ABR test) found in MM and HH groups than those in the respective CM and CH, MV and HV, including absolute wave III delays and interwave I-III latencies, which suggested that the irreversible auditory dysfunction caused by mercurial compounds. Furthermore, the alteration of lipid peroxidation (LPO), Na(+)/K(+)-ATPase activities, and nitric oxide (NO(x)) in the brain tissues contributed to the observed neurobehavioral dysfunction and hearing impairment. These findings provide evidence that fetuses were much more susceptible to the effects of mercurial compounds with regard to inducing severely neurotoxicological injuries as that found in human beings. The signaling of ROS/Na(+)-K(+)-ATPase/NO(x) plays a crucial role in the underlying mechanism for mercurial compound-induced toxic effects in offspring.

Mercury exposure and children's health

Acute or chronic mercury exposure can cause adverse effects during any period of development. Mercury is a highly toxic element; there is no known safe level of exposure. Ideally, neither children nor adults should have any mercury in their bodies because it provides no physiological benefit. Prenatal and postnatal mercury exposures occur frequently in many different ways. Pediatricians, nurses, and other health care providers should understand the scope of mercury exposures and health problems among children and be prepared to handle mercury exposures in medical practice. Prevention is the key to reducing mercury poisoning. Mercury exists in different chemical forms: elemental (or metallic), inorganic, and organic (methylmercury and ethyl mercury). Mercury exposure can cause acute and chronic intoxication at low levels of exposure. Mercury is neuro-, nephro-, and immunotoxic. The development of the child in utero and early in life is at particular risk. Mercury is ubiquitous and persistent. Mercury is a global pollutant, bio-accumulating, mainly through the aquatic food chain, resulting in a serious health hazard for children. This article provides an extensive review of mercury exposure and children's health.

Distribution patterns of inorganic mercury and methylmercury in tissues of rice (Oryza sativa L.) plants and possible bioaccumulation pathways

Whole rice plants (Oryza sativa L.) were collected at different typical mercury (Hg) contaminated sites during regular harvest periods to investigate the distribution of inorganic mercury (IHg) and methylmercury (MeHg) in tissues. The whole rice plants were divided into rice seed (brown rice), hull, root, stalk and leaf. Elevated IHg and MeHg concentrations were observed in rice plants cultivated in Hg mining area compared to those obtained from the control site, which attributed to the Hg contamination of soil compartments by the historical large-scale Hg mining/smelting and ongoing artisanal Hg smelting activities. Our observations showed that Hg in ambient air was the potential source of IHg to the above ground parts, whereas IHg concentrations in root were restricted to Hg concentrations in paddy soil. The rice seed has the highest ability to accumulate MeHg compared to the other tissues. MeHg in paddy soil is a potential source to tissues of rice plant. Our study suggested that newly deposited Hg is comparatively more easily methylated than old mercury in soil.

Quantification and fractionation of mercury in soils from the Chatian mercury mining deposit, southwestern China

Contents of total Hg and Hg fraction, organic matter, pH, grain size and chemical composition were measured to investigate the pollution characteristics and binding behavior of Hg in soils collected from the Chatian Hg mining deposit (CMD), southwestern China. The average concentration of Hg concentration in the CMD soils was 155 and 1,315 times higher than that in control soils and Chinese soils, respectively, suggesting that the CMD soils were heavily contaminated by the element. The finding was confirmed by Müller geoaccumulation index assessment with 75% very seriously polluted, 6.25% highly to very highly polluted and 18.75% moderately to highly polluted. Hg sources in the region were natural and anthropogenic: in addition to the pedogenic process and original geochemical situation, human mining-refining activities have also seriously impacted the redistribution of Hg in soils, especially in paddy soils. Based on the BCR protocol, soil Hg was divided into exchangeable (EXC), amorphous Fe-Mn oxides (AFe-MnOX), organic-crystalline iron oxides (OM-CFe) and residual (RES) fraction. The average percentage of the four fractions in the CMD followed the trend: RES (85.77%) > OM-CFe (12.44%) > AFe-MnOX (0.93%) ≥ EXC (0.86%), suggesting that the majority proportion of soil Hg in the study area remained of residual form inside the soil mineral matrix. However, their concentrations and percentages significantly varied among different locations and land use types. Soil physico-chemical parameters were key factors affecting the presence of Hg fraction. Generally, Hg fraction concentrations were positively correlated with the sand contents and soil pH values, which was presumably due to the basic anthropogenic input of Hg-containing materials and their similarity to sand in physical characteristics. However, organic matter caused adsorption-fixation and reduction-volatilization to coexist, which had opposite effects on Hg concentrations in soil, consequently exhibiting its dual nature.

Neurobehavioural effects, redox responses and tissue distribution in rat offspring developmental exposure to BDE-99

Polybrominated diphenyl ethers (PBDEs) have recently been shown to be on the increase in the environment and in human milk. The most commonly found PBDE congener in human milk is 2,2',4,4',5-penta BDE (BDE-99). The aim of the present study was to investigate the neurotoxic effects of BDE-99 (2 mg kg(-1)d(-1)) administration, from gestational day 6 to postnatal day (PND) 21, on neurobehavioural development and redox responses in offspring. Neurobehavioural development analysis revealed a delayed appearance of cliff drop and negative geotaxis reflexes in the exposed group. Furthermore, developmental exposure to BDE-99 also affected learning and memory functions during adolescence. On PND 37, the activity of superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px) was reduced, while increases in hydrogen peroxide, lipid peroxidation, nitric oxide and electron spin resonance signal intensities were observed in the hippocampus of BDE-99-treated animals. However, the activity of SOD and GSH-Px in the cerebellum and cerebral cortex was not significantly different between treated and control animals. The present study demonstrated that developmental BDE-99 exposure causes oxidative stress in the hippocampus of offspring by altering the activity of different antioxidant enzymes and producing free radicals. We demonstrated adverse effects of developmental exposure to BDE-99 associated with tissue concentrations very close to the current human body burden of this persistent and bioaccumulative compound.

Assessing noxious effects of dietary exposure to methylmercury, PCBs and Se coexisting in environmentally contaminated rice in male mice

Polychlorinated biphenyls and methylmercury are two of the most ubiquitous environmental contaminants in Guizhou province. Rice is eaten with almost every meal and provides more calories than any single food in Guizhou province. The estimated tolerable daily intake of total mercury, MeHg, Se and PCBs from Guizhou contaminated rice by Chinese people showed that MeHg and/or PCBs exceeded the corresponding limits. The aim of this study was to characterize the effects of exposure to environmental contaminated rice on neurobehavioral development and neurobiological disruptions in mice. Animals were treated from postnatal day (PND) 22 to 91. At PND 26-91 days of age, mice were tested for neurobehavioural development and neurochemical level changes. We showed that dietary exposure to environmentally contaminated rice gave rise to different changes in antioxidants. Reduced superoxide dismutase (SOD) activity and excess increased nitric oxide (NO) indicated aggravation of oxidative status after long-term dietary intake of Hg and PCBs. Neurobehavioral derangement in the central nervous system and significant delay in the Morris water maze test response on PND 91 are correlated with the increased of c-fos/c-jun expression levels in the cerebral cortex. These results suggest that MeHg neurotoxicity might be a greater hazard than that associated with PCB, but PCB may augment the neurobehavioral deficits caused by increased levels of mercury exposure. The simultaneous intake of selenium might have a protective effect on Hg accumulation in the body, and vitamin C might protect mice against the toxic effects of PCBs. However, the protective role of Se and vitamin C is very limited for multiple-agent pollution. Immediately early genes in the brain response to contaminated rice might be dependent on interaction among NO, NO synthase (NOS), SOD and reduced glutathione (GSH). We should be alert to mental health problems in human beings when any kind of Hg- and PCB-polluted food is consumed.

Mercury levels in fisherman and their household members in Zhoushan, China: impact of public health

Zhoushan Island is situated in the coast of the East China Sea. In order to assess the potential health risks associated with dietary consumption of mercury, hair samples from 59 piscatorial households, thirteen species of fish, crops and poultry samples were collected from the fishing villagers of Zhoushan. Total mercury (T-Hg) and methylmercury (MeHg) concentrations in the fathers' hair (mean, 5.7 and 3.8 microg/g) were approximately 2.5 and 2.1 times greater and 2.6 and 2.0 times higher than those of their wives (2.3 and 1.8 microg/g) and their children (2.2 and 1.7 microg/g), respectively. However, the mean quantity of the fish consumed by the fathers was 2.5 and 2.4 times higher than those of the mothers and children, implying that there was a wide variation in hair Hg concentrations between the fathers and the mothers and children of the same household, which was probably related to the quantity, frequency and type of fish consumed. The average T-Hg and MeHg concentrations in all species of fish were 0.26 and 0.18 microg/g, respectively. Approximately, 15% and 19% of the samples showed T-Hg and MeHg levels which exceeded the limit established by the Chinese National Standard Agency (CNSA) (0.3 and 0.2 microg/g), respectively. However, T-Hg and MeHg levels in crops, poultry, milk, drinking water, food oil and salt samples were all below the corresponding CNSA limit. The estimated total daily dietary intakes of T-Hg and MeHg via different food types showed that fish intake was the major source (>85%) of Hg exposure. The consumption advisories for the total quantity of thirteen species of fish were 69.3, 58.7 and 15.0 g per day for fathers, mothers and children, respectively.

Adsorption properties and gaseous mercury transformation rate of natural biofilm

Biofilms were developed on glass microscope slides in a natural aquatic environment and their mercury adsorption properties were evaluated. Results demonstrated that the biofilms contained a large number of bacterial cells and associated extracellular polymers. Mercury forms detected in the biofilms were mainly bound to residual matter and organic acids. The adsorption processes could be described by a Langmuir isotherm. The optimum conditions for adsorption of mercury to natural biofilm were an ionic strength of 0.1 mol/L, pH 6 and an optimum adsorption time of 40 min. The transformation rate was 0.79 microg gaseous mercury per gram of biofilm.

Mercury pollution in Guizhou, southwestern China - an overview

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.

Methylmercury accumulation in rice (Oryza sativa L.) grown at abandoned mercury mines in Guizhou, China

Mercury is a global pollutant that can transform into methylmercury, a highly toxic and bioaccumulative organic form. Previous surveys have shown that fish is the main source of human methylmercury exposure, whereas most other food products have an average value below 20 microg/kg and primarily in the inorganic form. This paper reports that methylmercury in rice (Oryza sativa L.) grown at abandoned mercury mining areas contained levels >100 microg/kg in its edible portion and proved to be 10-100 times higher than other crop plants. The daily adult intake of methylmercury through rice consumption causes abnormally high methylmercury exposure to humans. The results demonstrate that rice is a methylmercury bioaccumulative plant and the main methylmercury source for human exposure in the areas studied.

Mercury concentration in hair samples from Chinese people in coastal cities

This investigation was made to estimate current normal concentrations of total mercury in the hair of Chinese coastal people. Hair samples were collected from 659 healthy inhabitants in the areas along the coast and the rivers (such as Shanghai, Ningbo, Dalian, Xiamen, and Zhoushan) of China from Feb. 2005 to June 2006. Total mercury concentrations in the samples were analyzed by the cold vapor atomic adsorption spectrometry method (CVAAS). The results showed the geometric mean concentration of total mercury in the hair of the total population (N = 659) was 0.83 microg/g, and the geometric mean of the concentrations of total mercury in the hair of the male (0.94 microg/g, 338 inhabitants with an average age of 35.2, age 2-93) was higher than that of the female (0.72 microg/g, 321 inhabitants with an average age of 39.1, age 1-90). In both the male and female, the mean concentrations of total mercury in hair increased with age, and then gradually decreased. There was a significant correlation between the total hair mercury and the place of residence (p < 0.01), and total hair mercury was the highest in volunteers who lived in Zhoushan. Over half of all sample concentrations were below the USEPA-recommended 1 microg/g. In Zhoushan (males, 2.44 microg/g; females, 1.94 microg/g) and Ningbo (males, 1.06 microg/g; females, 1.02 microg/g), it exceeded the recommended level. Very little females (0.3%) of reproductive age showed hair mercury levels close to 10 microg/g. It was thus concluded that fish consumption was a major current route for mercury exposure in China.

Detection of mercury-, arsenic-, and selenium-containing proteins in fish liver from a mercury polluted area of Guizhou Province, China

Mercury (Hg)-, selenium (Se)-, and arsenic (As)- containing proteins in liver tissues of bighead carp and grass carp sampled from a mercury-polluted area of Wanshan, Guizhou Province, China, were separated by thin-layer isoelectric focusing. The relative content of Hg, Se, and As in protein bands was measured with synchrotron radiation x-ray fluorescence. The results indicated that there were at least 3 Hg-containing bands with pI 3.7, 4.8, and 6.2 in liver of bighead carp and 1 Hg-containing band with pI 6.2 in grass carp. Se and As were found in the Hg-containing bands 3.7 in bighead carp and 6.2 in grass carp. The bands may be corresponding to the antagonistic effect of Se against the toxicity of Hg and As. In addition, Hg and As often coexist in the same band, suggesting that the two elements may be involved in the same metabolic processes.