Mercury pollution in Wuchuan mercury mining area, Guizhou, Southwestern China: the impacts from large scale and artisanal mercury mining

Towards a better understanding of ethylmercury in the environment: Addressing propylation derivatization artifact and verifying its occurrence in Chinese wetlands

Ethylmercury (EtHg), similar to methylmercury (MeHg), is highly neurotoxic and bioaccumulative. Although recent studies suggested its occurrence in natural soils and sediments, the common propylation derivatization for EtHg analysis might generate EtHg artifacts, potentially leading to its overestimation in environmental samples. Furthermore, the extensive environmental prevalence of EtHg remains unverified, keeping its importance largely uncertain. This study investigated the formation of EtHg artifacts during propylation derivatization, evaluating artifacts formation and recoveries under different extraction methods with real samples, and confirmed the widespread occurrence of EtHg in Chinese wetlands. EtHg artifacts were obviously present during the propylation derivatization and strongly dependent on the levels of Hg2+ (0.1-10 ng) in the derivatization solution (R² = 0.99), accounting for 1.38-2.14% of Hg2+. CuSO4-HNO3CH2Cl2 extraction (effectively removing Hg2+) combined with propylation derivatization offers excellent recovery (81-86%) and low artifacts (< LOD: 1.98 × 10-4 ng/g) for EtHg measurement in soils/sediments, with results aligning with those from online solid phase extraction-high performance liquid chromatography-inductively coupled plasma mass spectrometry (R2 = 0.99). Additionally, we observed the occurrence of EtHg in soil and sediment samples across 14 Chinese wetlands, with concentrations varying from 6.08 to 171 pg/g, similar to MeHg concentrations at some sites. EtHg positively correlates with MeHg, total Hg, and total organic carbon across all samples, indicating a possible biological formation. These findings help better understand and predict the prevalence of EtHg in wetlands and its key role in environmental Hg cycle.

Environmental and human health risk assessment of soils in areas of ore mineralization and past gold-mining activity

The patterns of the potentially toxic elements (PTEs: Cr, Fe, Ni, Cu, Zn, As, Mo, Pb, Hg) distribution in soils were studied together with the health risk assessment in the area of ore mineralization, past gold activity, and tailing effects of the Sarala gold-ore group located in the Republic of Khakassia, Russia. High PTE concentrations were found in soils with the presence of potential negative impact on human health based on the following: local background investigation, according to statistics; geochemical, environmental, and human health risk calculations; and comparative analysis using international and local reference, such as continental crust, clarke, and permissible concentrations. Sources of PTE soil enrichment and pollution were statistically identified in ascending order of degree: geogenic (local background) < geogenic-technogenic (sites with geological exploration traces - trenches) < technogenic (waste tailings). The main pollutants are Hg and As which showed moderate to significant ecological risk. Negative impact of Cr on soils was found. The pollution degree and toxicity (moderate to significant) of other PTEs increase in the location of ore mineralization zone with exploration trenches and waste tailings. Arsenic poses a carcinogenic risk to adults and children upon contact with polluted soils and non-carcinogenic effect on children in areas affected by tailings and ore mineralization zone. The non-carcinogenic effect of Fe on children was found in soils of all sites. The results provide useful information regarding the studied PTEs and their impact on the environment and human health. Such information can be helpful for the state-level decision-making process when addressing solutions for contaminated areas.

Heavy metal contamination in duck eggs from a mercury mining area, southwestern China

Objective

Mercury (Hg) contamination in the environment around mercury mines is often accompanied by heavy metal contamination.

Methods

Here, we determined concentrations of chromium (Cr), zinc (Zn), strontium (Sr), barium (Ba), and lead (Pb) in duck eggs from a Hg mining area in Southwest China to assess the contamination and health risk.

Results

Duck eggs obtained from the mining area exhibit higher concentrations of Cr, Zn, Sr, Ba, and Pb compared to those from the background area, with egg yolks containing higher metal levels than egg whites. Specifically, the mean Cr, Zn, Sr, Ba, and Pb concentrations of duck eggs from the Hg mining area are 0.38, 63.06, 4.86, 10.08, and 0.05 μg/g, respectively, while those from the background area are only 0.21, 24.65, 1.43, 1.05, and 0.01 μg/g. Based on the single-factor contamination index and health risk assessment, heavy metal contamination in duck eggs poses an ecological risk and health risk.

Conclusion

This study provides important insight into heavy metal contamination in duck eggs from Hg mining areas.

Assessment of mercury distribution and bioavailability from informal coastal cinnabar mining - Risk to the marine environment

Coastal cinnabar mining commenced in 2010 around Luhu on Seram (Ceram) Island, Indonesia. This study investigates the ore characteristics and environmental distribution and bioavailability of mercury in coastal sediments from eight sites adjacent to, and north and south of the mining area. Sediment and ore samples were digested using 1:3 HNO3:HCl for total extractable metal determination and separate samples were extracted with 1.0 HCl for bioavailable metals (Hg, Cu, Zn, Cr, Ni and Pb). Analysis was completed using inductively coupled plasma-mass spectrometry. Ore defined by miners as 'first class ore' was around 50 % cinnabar. Mercury concentrations were extremely elevated in near coastal sediments (up to 2796 mg/kg) with bioavailable concentrations exceeding 450 mg/kg. Marine sediments elevated in mercury extend to the north and south of the coastal mine site and cover in excess of 14 km. Total organic carbon in marine sediments was relatively low (predominately <0.6 %) suggesting mercury methylation will likely be slow, however, inorganic mercury is a known toxicant. Other metals of environmental concern (Cu, Zn, Cr, Ni and Pb) in sediments were not strongly associated with the mining operations, rather were elevated around coastal villages, but not at concentrations that raise immediate concerns.

Ecological restoration reduces mercury in corn kernel and the distinction of mercury in corn plants in rural China - A case in Wuchuan mercury mining area

Corn is a crucial crop in China and is widely cultivated in the mercury (Hg) mining region of Guizhou. This study analyzed the Hg content in soil and corn plant samples from the Wuchuan Hg mining area (WCMA) and the surrounding non-Hg mining regions (SNMR). The findings suggest that ongoing ecological rehabilitation and environmental conservation measures in the WCMA have significantly decreased the Hg content in corn kernels. The Hg concentration in different parts of the corn plant varied, being higher in the roots, tassels, and leaves and lower in kernels and stalks. Hg stored in corn plant growing in the WCMA primarily originates from the soil (55.4%), while in the SNMR, it mainly comes from the atmosphere (74.9%). Despite counted only about 7% of the total plant mass, corn roots play a crucial role in soil Hg pollution remediation when corn is used for remediation. Household corn residues burning release about 58.5% and 66.9% of the stored Hg in corn plants growing in the WCMA and the SNMR, respectively, into the atmosphere. Our findings indicate that corn cultivation acts as a reservoir for both soil and atmospheric Hg in the SNMR, while in the WCMA, it serves as a source of atmospheric Hg.

Assessment of hydrological, geological, and biological parameters of a river basin impacted by old Hg mining in NW Spain

Mercury (Hg) is a toxic metal that can cause adverse effects for the health of ecosystems. The Caudal River is one of the main rivers in the Asturias region (NW Spain), whose basin is highly anthropized, hosting several Hg mines, closed in the last century. Arsenic (As) is also found in the mineral paragenesis of the Hg deposits, posing a greater environmental risk. In the mining sites, remaining old facilities and tailings continue to release these elements into the environment. In this work, samples of fluvial sediments and water were taken, both in areas affected by anthropic activity and in pristine areas, in order to establish the background levels for the critical elements. The mineralogical study of the sediments, combined with EDS microanalysis, is useful to identify mineralogical traps such as Fe oxides or clays to retain the As. The As content in all sampled sediments is above the threshold effect levels (TEL), the possible effect range within which adverse effects occasionally occur, according to the Canadian Sediment Quality Guidelines for the Protection of Aquatic Life. This fact is related to a naturally high geochemical background in the basin, due to the existing mineral deposits. The PEL threshold (the probable effect range within which adverse effects frequently occur) is exceeded by more than an order of magnitude in the sediments downstream of the Hg mines. In these points, the As content in the water, exceeding 700 μg L-1 As, is also above the quality standard established in Spanish legislation. As a result, the Caudal River tributaries in the lower part of the basin do not reach a good ecological state, according to the Hydrological Planning Office, and in some cases their state is deficient, showing low richness and high dominance of macroinvertebrates. Although the concentrations decrease with distance from the source, these findings justify the low ecological quality of the affected watercourses.

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.

Ultrasensitive detection and efficient removal of mercury ions based on covalent organic framework spheres with double active sites

In present work, a new spherical covalent organic framework (TFPB-APTU COF) with good photoelectric property and double active sites (secondary amine (-NH-) group and sulfur (S) atom) was prepared for ultrasensitive detection and efficient removal of mercury ions (Hg2+). The -NH- group and S atom can capture free Hg2+ by coordination and chelation interaction, and the related steric hindrance effect reduces the photocurrent signal of the TFPB-APTU COF, resulting in the highly sensitive photoelectrochemical analysis of Hg2+ with a wide linear response range (0.01-100000 nM) and low detection limit (0.006 nM). On the other hand, the developed TFPB-APTU COF has large removal capacity (2692 mg g-1), good regeneration capability, and high removal speed for Hg2+ removal based on the double active sites (-NH- group and S atom), large specific surface area and porous spherical structure. The developed TFPB-APTU COF spheres show great potential in monitoring and treatment of environmental pollution of Hg2+.

Effects of long-term zinc smelting activities on the distribution and health risk of heavy metals in agricultural soils of Guizhou province, China

To assess the effect of zinc smelting on environment and human health, the concentration, distribution, sources and health risk of eight heavy metals (Pb, Cd, Cu, Zn, Cr, Ni, Mn, and As) were investigated from agricultural soils in a long-term Zn smelting area in Guizhou, China. Different health risk assessment methods and models were used to access health risks. The results show that the concentrations of all the eight heavy metals were significantly higher than their corresponding background values (p < 0.05). Pb, Cd, and As were the most contaminated elements, with 93.6%, 90.3% and 48.4% of agricultural soil samples higher than the risk screening values, respectively. Statistical analysis indicated that Pb, Cd, Cu, Zn, Mn, and As could be mainly accounted for Zn smelting activities, while Cr and Ni may be generally more controlled by natural sources. The geo-accumulation index (Igeo) suggested that the most seriously contaminating heavy metals were Pb, Cd, and Zn, with 96.8%, 90.3%, and 96.8%, respectively, of the soil samples classified as moderately to extremely contaminated. The non-carcinogenic health risk associated with Pb, Cd and As were observed for children, meanwhile, the carcinogenic risk due to As was found for both adults and children. Regardless of cancer risk or non-cancer risk, local children are at greater risk than adults. Therefore, Pb, Cd and As play the leading role to cause potential health risks in the study area, which need to be paid more attention and also effective control measures should be taken.

Environmental impact of potentially toxic elements on soils, sediments, waters, and air nearby an abandoned Hg-rich fahlore mine (Mt. Avanza, Carnic Alps, NE Italy)

The decommissioned fahlore Cu-Sb(-Ag) mine at Mt. Avanza (Carnic Alps, Italy) is a rare example of exploited ore deposits, as the tetrahedrite (Cu6[Cu4(Fe,Zn)2]Sb4S13) is the main ore mineral found. This multi-compartmental geochemical characterisation approach provides one of the first case studies regarding the geochemical behaviour and fate of Hg, Sb, As, Cu, and other elements in solid and water matrices and of Hg in the atmosphere in an environment affected by the mining activity of a fahlore ore deposit. Elevated concentrations of the elements (Cu, Sb, As, Pb, Zn, Hg) associated with both (Zn-Hg)-tetrahedrite and to other minor ore minerals in mine wastes, soils, and stream sediments were observed. Concentrations in waters and stream sediments greatly decreased with increasing distance from the mining area and the Igeo index values testify the highest levels of sediment contamination inside the mine area. Thallium and Ge were associated with the "lithogenic component" and not to sulfosalt/sulphide minerals. Although mine drainage water often slightly exceeded the national regulatory limits for Sb and As, with Sb being more mobile than As, the relatively low dissolved concentrations indicate a moderate stability of the tetrahedrite. The fate of Hg at the investigated fahlore mining district appeared similar to cinnabar mining sites around the world. Weak solubility but the potential evasion of gaseous elemental mercury (GEM) into the atmosphere also appear to be characteristics of Hg in fahlore ores. Although GEM concentrations are such that they do not present a pressing concern, real-time field surveys allowed for the easy identification of Hg sources, proving to be an effective, suitable high-resolution indirect approach for optimising soil sampling surveys and detecting mine wastes and mine adits.

Total mercury in different egg tissues provides insights to mercury metabolisms in bird bodies

Mercury (Hg) pollution in birds has been widely reported, but the metabolism of Hg in bird bodies remains unclear. Measurement of Hg concentrations in bird tissues (muscles and organs) could provide insights into the metabolism of Hg in bird bodies, however, this approach is often invasive. To avoid invasive procedures, we conducted feeding experiments using chickens and used eggs as a proxy for understanding Hg metabolism in chicken bodies. For the control group, various THg concentrations were observed in egg whites, egg yolks, and eggshells, but the THg concentration trends for different egg tissues were not statistically different (P > 0.05). For the Hg feeding group (0.3 mg/kg body weight, feeding once), Hg peaks were observed in egg yolks and egg whites at different time periods, suggesting different response time to dietary Hg in chicken body tissues. Mercury in egg yolks peaked at Day 6, suggesting their quick response to dietary Hg. Egg whites reached Hg peak at Day 20, exhibiting a slower response to dietary Hg. Eggshells did not show a Hg peak, perhaps due to their predominant inorganic components that do not trigger Hg bioaccumulation. We measured THg_yolk/THg_white ratios in various chicken eggs purchased from three areas in Guizhou, SW China. The THg_yolk/THg_white ratios for Huaxi, Hezhang and Wuchuan were 1.33 (0.57-2.41), 7.89 (4.27-19.47) and 2.64 (1.68-4.22), respectively, to suggest different exposure history for chickens. This study provides new insights into the metabolism and lifetime of Hg in bird bodies.

Unravelling the interactive effect of soil and atmospheric mercury influencing mercury distribution and accumulation in the soil-rice system

Mercury (Hg) accumulation in rice is an emerging health concern worldwide. However, sources and interactions responsible for Hg species accumulation in different rice tissues are still uncertain. Four experimental plots were carefully designed at an artisanal Hg mining site and a control site to evaluate the effect of atmospheric and soil Hg contents on Hg accumulation in rice. We showed that inorganic Hg (IHg) contents in rice tissues grown either in contaminated or control site soil (non-contaminated soil) were higher at Hg artisanal mining site than those at the control site. Elevated total gaseous mercury (TGM) levels in ambient air were the predominant source of IHg to rice at the Hg mining area. Methylmercury (MeHg) concentrations in rice plant tissues increased in proportionality with MeHg contents in paddy soil. Our results suggest that both atmosphere and soil Hg sources have been impacted the IHg accumulation in rice. Above ground rice tissues, grains, leaves, and stalk accumulated IHg from both atmosphere and soil to varying degrees. Nonetheless, the study also provides the first direct evidence that atmospheric Hg accumulated by above-ground rice tissues could be translocated to below-ground tissues (roots). However, the extent to which atmosphere or soil Hg contributes to IHg in rice tissues may vary with each source's concentration gradient at the given site. No evidence of in planta Hg methylation was found during the current study. Hence, paddy fields are potential MeHg production sites, whereas paddy soil is a unique MeHg accumulation source in rice plants. This study expands and clarifies the contribution of various sources involved in Hg accumulation in the soil rice system. The findings here provide the basis for future research strategies to deal with the global issue of Hg contaminated rice.

Mercury uptake by Paspalum distichum L. in relation to the mercury distribution pattern in rhizosphere soil

Paspalum distichum L. was tested to evaluate their phytoremediation capacity for Hg contaminated soil through analyzing the dissipation of Hg in soil through a greenhouse study by using self-made rhizos box. Original soil samples were collected at Hg mining site with serious Hg contamination and a control site, respectively. Planting of P. distichum. L last for 60 days. Soil and plant samples were collected from four periods (0 d, 20 d, 40 d, and 60 d) and soil samples were collected from five different rhizosphere distance in horizontal direction (0-2 cm, 2-4cm, 4-6cm, 6-8cm, 8-10cm). The results showed that the presence of P. distichum. L significantly accelerated the Hg dissipation in soil compared with control. Hg concentration in the rhizospheric soil was affected by the plant growth period and the distance to the plant roots. The closer of soil to the root of P. distichum. L, the lower mercury concentration in soil. During the 60-day growing period, the concentrations of total Hg (THg) and methylmercury (MeHg) reduced by 45% and 64%, respectively, in the rhizosphere (0-2cm) of Hg contaminated soil. However, MeHg concentration was increased near the roots (0-4 cm) during the initial growing period (0-20 d), which may be attributed to the influence of root exudates. Root is the major part for Hg accumulation in P. distichum. L. The low ratio between Hg concentrations in underground and aboveground tissues indicated that it seemed difficult for Hg translocation from root to shoot. The highest THg (9.71 ± 3.09 μg·g^-1) and MeHg (26.97 ± 0.98 ng·g^-1) value in root of P. distichum. L were observed at the 20^th day when P. distichum. L grown in Hg contaminated soil. The results of chemical fractions analyses showed that elemental Hg and residual Hg were the two major speciations followed by organic bound Hg in the Hg contaminated soil, which indicated the high bioavailability and ecological potential risk of Hg in Hg contaminated soil.

Mercury horizontal spatial distribution in paddy field and accumulation of mercury in rice as well as their influencing factors in a typical mining area of Tongren City, Guizhou, China

PURPOSE

To make up for the deficiency of the distribution characteristics of mercury (Hg) pollution in soil and rice in a specific area, the relationship between more than ten soil indices and Hg in soil-rice system was analysed, and the main factors affecting mercury accumulation in rice were screened out. So as to provide reliable theoretical and scientific basis for the regulation and safe utilization of Hg-contaminated soil.

METHODS

The Hg-polluted area of Siqian Dam, with a paddy field area of 1.34 million square meters, was selected as the research unit. Soil and corresponding rice samples were collected and analysed. Then, common Kriging interpolation was used to explore the spatial distribution differences of mercury content between soil and rice, Pearson correlation analysis and stepwise linear regression were used to analyse the relationship between mercury content and 14 soil indices.

RESULTS

In the study area, the total mercury(THg) content in soil and rice was as high as 30.60 mg/kg and 160.19 µg/kg, respectively, and the methyl mercury(MeHg) content was as high as 14.56 µg/kg and 40.32 µg/kg, respectively, indicating that mercury pollution in soil and rice was serious. The horizontal spatial distribution of soil THg and MeHg was different. Flood with its sediment and topography were the main reasons for the uneven distribution of Hg content in the region. The spatial distribution of Hg was different between rice and soil. There was no significant correlation between rice and soil THg, but there was a significant correlation between rice and soil MeHg content. Among the 14 soil indices, available potassium was a vital index affecting the accumulation of Hg in rice, followed by pH, Zn, Mn and Fe.

CONCLUSIONS

The results showed that in weakly acidic and fertile soil, the appropriate reduction of soil pH, OM and available Se and Cr contents could inhibit soil Hg methylation, the reduction of potassium fertilizer application could further reduce rice Hg accumulation.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s40201-021-00711-z.

A new method of predicting the contribution of TGM to Hg in white rice: Using leaf THg and implications for Hg risk control in Wanshan Hg mine area

Rice plants accumulate Hg from the soil and ambient air, however, evaluating the contribution of Hg from these two sources remains challenging. Here, we proposed a practical method to predict the contribution of total gaseous mercury (TGM) to Hg in white rice in Wanshan Hg mine area (WMM). In this study, rice was planted in the same low-Hg soil at different sites of WMM with varying TGM levels. Comparing to the control sites at IG (Institute of Geochemistry, Guiyang), TGM is the dominant source of Hg in rice leaves and white rice at TB (Tianba) and ZJW (Zhangjiawan) sites of WMM. Subsequently, a good correlation between the Hg concentrations in rice leaves and the concentration contributions of TGM to Hg in white rice was obtained. Such a correlation enabled feasible quantification of the contribution of TGM to Hg in white rice collected from the Wanshan Hg mine. The contribution of TGM to Hg in white rice across the WMM area was also estimated, demonstrating that white rice receives 14-83% of Hg from the air. Considering the high contribution of TGM to Hg in white rice, we compared the relative health risks of Hg via inhalation and rice consumption and found that inhalation, rather than rice consumption, was the major pathway for bioaccessible Hg exposure in adults at high-TGM sites. This study provides new knowledge of Hg biogeochemistry in Hg-mining areas.

Holistic health risk assessment in an artisanal mercury mining region in Mexico

Mexico is one of the world's leading mercury producers and exporters. However, mercury mining is carried out using artisanal procedures, which highly impact ecosystems. In the municipality of Pinal de Amoles, Queretaro, Mexico, artisanal mercury mining (AMM) is practiced in a region that has been categorized as a Biosphere Reserve. Therefore, a holistic health risk assessment for mercury was performed in the region, including environmental monitoring (air, water, and soil) and mercury exposure in both humans (children, women, and miners) and biota (plants, rodents, and worms). The atmospheric mercury determination was carried out using the JEROME® J405 analyzer, whereas total mercury in environmental and biological samples was determined by atomic absorption spectrophotometry/cold vapor. Results showed that mercury concentrations in the environmental and biological matrices exceeded their respective reference values. These results demonstrate the direct influence of AMM in the increasing levels of mercury in all the components of the studied ecosystem. Therefore, comprehensive intervention strategies must be implemented to reduce and prevent human health and ecological risks due to the presence of mercury. In this regard, the Minamata Convention for mercury control should include biomonitoring programs not only for humans but also for critical ecological receptors in polluted ecosystems.

Neurodevelopment and exposure to neurotoxic metal(loid)s in environments polluted by mining, metal scrapping and smelters, and e-waste recycling in low and middle-income countries

This review covers a wide body of literature to gain an understanding of the impacts of informal activities related to metal extraction (primary mining and recycling) on early life exposure to neurotoxicants and on neurodevelopment. In primary mining, gold extraction with Hg amalgamation is the main environmental cause of Hg pollution in most artisanal small-scale gold mining (ASGM) activities around the world. Nevertheless, in Sub-Saharan Africa (SSA), Pb disrupted from gold-related ores, mining, and artisanal cookware production are an important neurotoxicant that seriously contaminates the affected population, with devastating effects on children. In e-waste recycling settings, the range of neurotoxic substances that contaminate mothers and children is wider than in primary mining environments. Thus, Hg and Pb are major pre- and postnatal neurotoxicants affecting children in the informal metal extraction activities and SSA countries show the highest record of human contamination and of neurotoxic effects on children. There are additional sources of neurotoxic contamination from mining and metal processing activities (cyanide tailing in South America and SSA) and/or co-exposure to Hg-containing products such as cosmetics (soaps and Hg-based skin lightning creams in Africa) and pediatric Thimerosal-containing vaccines (TCVs, that breaks down to ethyl-mercury) in current use in middle and low income countries. However, the action of these neurotoxicants (per se or in combination) on children needs more attention and research. Studies show a negative association between biomarkers of all environmental metal(loid)s (As, Cd, Hg, Mn, and Pb) studied and neurodevelopment in young children. Sadly, in many unregulated activities, child labor is widely employed, thus presenting an additional occupational exposure. Children living in polluted environments related to metal processing are disproportionately exposed to a wide range of co-occurring neurotoxic substances. The review showed compelling evidence from highly representative parts of the world (Africa, Asia, and Latin America) that the studied neurotoxic substances negatively affected areas of the brain associated with language, memory and executive function, as well as psychosocial behavior. Protecting the environment and children from unregulated and highly polluting metal extraction and processing are inextricably intertwined and deserve urgent attention.

Significant mercury efflux from a Karst region in Southwest China - Results from mass balance studies in two catchments

Karst regions have long been recognised as landscapes of ecological vulnerability, however the mass balance and fate of mercury (Hg) in karst regions have not been well documented. This study focused on the largest contiguous karst area in China and investigated Hg mass balance in two catchments, one with high geological Hg (Huilong) and the other representative of regional background Hg (Chenqi). The mass balance of Hg was calculated separately for the two catchments by considering Hg in throughfall, open field precipitation, total suspended particulate matter (TSP), litterfall, fertilizer, crop harvesting, air-surface Hg⁰ exchange, surface runoff and underground runoff. Results show that litterfall Hg deposition is the largest loading (from atmosphere) of Hg in both catchments, accounting for 61.5% and 38.5% of the total Hg input at Huilong and Chenqi, respectively. Air-surface Hg⁰ exchange is the largest efflux, accounting for 71.7% and 44.6% of the total Hg output from Huilong and Chenqi, respectively. Because both catchments are subject to farm and forest land use, cultivation plays an important role in shaping Hg fate. Mercury loading through fertilizer was ranked as the second largest input (28.5%) in Chenqi catchment and Hg efflux through crop harvest was ranked as the second largest output pathway in both Huilong (27.0%) and Chenqi (52.9%). The net Hg fluxes from the catchments are estimated to be 1498 ± 1504 μg m^-2 yr^-1 and 4.8 ± 98.2 μg m^-2 yr^-1. The significantly greater magnitude of net Hg source in Huilong is attributed to higher air-surface Hg⁰ exchange. The output/input ratio of Hg in this study was much greater than has been reported for other forest or agricultural ecosystems and indicates that the karst region of Southwest China is a significant source of atmospheric Hg. The results of this study should be considered in the development of pollution control policies which seek to conserve fragile karst ecosystems characterised by high geological background of Hg.

Novel fluorescent probe based on dicoumarin for rapid on-site detection of Hg2+ in loess

It is momentous to exploit rapid, specific and on-site detection methods for mercury ion (Hg²⁺) in loess, as the severe toxicity of Hg²⁺ and the fragile ecological environment of Loess Plateau. In this paper, a novel fluorescent probe DC-Hg (Dicoumarin-Hg) was synthesized by 3-hydroxybiscoumarin and phenyl thiochloroformate at room temperature. DC-Hg could exclusively combine with Hg²⁺ to 'turn-on' yellow fluorescence at 530 nm among various other metal ions. The relationship between the remarkable increase in intensity and concentration of Hg²⁺ was associated with photoinduced electron transfer (PET), which was founded by Job's plot and ¹H NMR. The limit detection of DC-Hg showed to 85.25 nM in aqueous medium, which could be applied to varying situations. For the loess samples, they were only extracted by hand-shake and filtration for quickly complete the treatment operation on site, and the results proved that DC-Hg could satisfactorily detect the Hg²⁺ in mercury pollution areas.

Four xanthene–fluorene based probes for the detection of Hg2+ ions and their application in strip tests and biological cells

Four new fluorescent probes based on the xanthene structure to detect mercury ions with different colors of fluorescence have been reported.

Mercury in rice paddy fields and how does some agricultural activities affect the translocation and transformation of mercury - A critical review

Human exposure to methylmercury (MeHg) through rice consumption is raising health concerns. It has long been recognized that MeHg found in rice grain predominately originated from paddy soil. Anaerobic conditions in paddy fields promote Hg methylation, potentially leading to high MeHg concentrations in rice grain. Understanding the transformation and migration of Hg in the rice paddy system, as well as the effects of farming activities, are keys to assessing risks and developing potential mitigation strategies. Therefore, this review examines the current state of knowledge on: 1) sources of Hg in paddy fields; 2) how MeHg and inorganic Hg (IHg) are transformed (including abiotic and biotic processes); 3) how IHg and MeHg enter and translocate in rice plants; and 4) how regular farming activities (including the application of fertilizer, cultivation methods, choice of cultivar), affect Hg cycling in the paddy field system. Current issues and controversies on Hg transformation and migration in the paddy field system are also discussed.

Pollution and health risk assessment of toxic metal(loid)s in soils under different land use in sulphide mineralized areas

Toxic metal(loid) pollution in sulphide mineralized area has been increasingly concerned. In the present study, the pollution characteristics and the health risk of Hg, As, Tl and other metal(loid)s in soils under different land use, from a rural area impacted by Tl-Hg-rich sulphide mineralization, were assessed using statistical analysis, enrichment factor (EF), potential ecological risk index (RI) and health risk assessment model. The results showed that Tl, Hg and As were highly enriched in the mine area due to the historic sporadic mining activities, and Tl, Hg and Sb were enriched in the peripheral area. Hg and Tl pollution in soils of the mine area impacted by past mining activities posed high ecological risk. High contents and enrichment of Tl and Hg in forest/grass land had a greater impact on the ecological risk in the mine area; whereas Tl and Hg in the grain land and vegetable land dominated the soil ecological risk in the peripheral area. Human health risk assessment indicated that children are more sensitive and vulnerable to toxic metal(loid)s in soils than the adults. Hg, Tl and As have potential non-carcinogenic risk to local children and adults. The HQ levels for different exposure pathways of toxic metal(loid)s were in the order of ingestion > dermal contact > air inhalation for Tl and As, and dermal contract > ingestion > air inhalation for Hg. For carcinogenic risk, all the mean CR values of ingestion in the mine area were higher than 10^-4, indicating seriously potential risk. The descending order of ILCR via different pathways was the same as the HQ, for which ingestion was predominant, followed by dermal and air inhalation. The findings may help provide basic knowledge and guidelines for toxic metal(loid) pollution remediation in similar sulphide mineralized areas.

Vegetable Houttuynia cordata Thunb. as an important human mercury exposure route in Kaiyang county, Guizhou province, SW China

Consumption of mercury (Hg) contaminated vegetable is one important pathway of Hg expose to humans. In this study, Hg contents in a popular vegetable, Houttuynia cordata Thunb. (HCT), and its growing soils in Kaiyang county in Guizhou province of southwest China were investigated. Health risk related to Hg exposure through consumption of this vegetable was evaluated for the first time. Hg contents in HCT were found to be much higher in three towns in western Kaiyang county (42.3 ± 48.2 μg/kg, FW), where former Hg mines located, than that in other towns (7.6 ± 5.0 μg/kg, FW). Hg contents in HCT were also higher than in the other five vegetables (Chinese cabbage, Lettuce, Tomato, Carrot and White radish). Consumption of HCT may account for 37.4-61.1% of total vegetable Hg intake of local people in Kaiyang county. Hg concentration in HCT positively correlated with that in soil (r² = 0.311, p < 0.01), especially, the labile Hg species (F_C1, r² = 0.796, p < 0.01) and the elemental Hg that is bound to the crystalline oxides (F_C3, r² = 0.711, p < 0.01), and negatively correlated with Hg that is bound to humic and fulvic complexes (F_C2, - 0.304). Estimated daily intake (EDI) and target hazard quotient (THQ) results shown that Hg expose risk is much higher for children than adults, likely due to their different eating habits and the amount of snack intake.

Occurrence and risk assessment of total mercury and methylmercury in surface seawater and sediments from the Jiaozhou Bay, Yellow Sea

The Jiaozhou Bay is a semi-enclosed bay located in the middle of the Yellow Sea. Effluents from wastewater treatment plants have been carried into the bay, which has significantly increased the deposition of mercury. The spatial distributions of total mercury (THg) and methylmercury (MeHg) in dissolved state, in suspended matters of seawater and surface sediments at 26 locations inside the Jiaozhou Bay and five surrounding rivers in April 2018 were examined. The contents of THg and MeHg found along the eastern coast were higher than those found along the western coast, which indicated the impact of human activities (river input) on the Jiaozhou Bay. The partition coefficient (LogKd) was used to express the distribution relationships of THg and MeHg in suspended matters and dissolved state, and it was concluded that suspended matter was the main reservoir of mercury in Jiaozhou Bay seawater. The correlations between contents and physicochemical properties of seawater showed that THg and MeHg concentrations in seawater decreased with increasing salinity and pH. The effects of the mean grain diameter (MGD) and sediment organic matter (SOM) on the THg and MeHg in surface sediments were also discussed. Principal component analysis (PCA) was used to obtain the factors determining the methylation proportion in the surface sediments, indicating that the combination of human activities and natural processes affected the degree of methylation in the sediments. The spatial distribution of THg, MeHg and MeHg% was suggested to be disturbed by the interaction of natural processes and human activities (river input) by the correlation analysis of the corresponding pollutant concentrations among seawater and. Although the concentrations of THg and MeHg in seawater and sediments of the Jiaozhou Bay did not exceed the Chinese regulatory standards, the pollution levels of THg and MeHg were comparable to those in other bays in the world.

Newly deposited atmospheric mercury in a simulated rice ecosystem in an active mercury mining region: High loading, accumulation, and availability

Mercury (Hg) mining activities are an important anthropogenic source of atmospheric Hg. The Xunyang Hg mine located in Shaanxi Province is the largest active Hg producing centre in China. To understand the biogeochemical processes of atmospheric Hg through Hg mining activities, six groups of experimental pots were carefully designed to investigate the effect of Hg mining activities on Hg contamination from atmospheric deposition in the local surface soils. Based on the variations of Hg in the soil from the experimental pots, the deposition flux and loading of Hg in the Xunyang Hg mining district were investigated. The results showed that the average concentration of total gaseous mercury (TGM) as high as 193 ± 122 ng m^-3 was observed in the ambient air, which was orders of magnitude higher than that in remote areas. The average deposition flux and annual loading of atmospheric Hg were 72 mg m^-2 y^-1 and 10 t y^-1, respectively. The dominant atmospheric Hg deposition is within a distance range of 6.0-12 km from the Hg retorting facility, accounting for approximately 85% of the total Hg loading. After 14 months of exposure, total mercury (THg) concentrations in the soil from the experimental pots increased 0.35-9.5 times, and the highest concentrations of methylmercury (MeHg) (3.7 ± 2.9 μg kg^-1) in soil were observed in February. Concentrations as high as 643 μg kg^-1 THg and 13 μg kg^-1 MeHg in rice were observed in the second experimental year. Elevated concentrations of both THg and MeHg in rice indicated that the newly deposited atmospheric Hg was bioavailable, readily methylated, and taken up by rice, suggesting that the ongoing Hg mining activities cause serious Hg contamination in the soil-rice ecosystem and posed a threat to local residents in the Xunyang Hg mining area.

Anthropogenic influences on mercury in Chinese soil and sediment revealed by relationships with total organic carbon

Rapid industrialization has led to high levels of mercury (Hg) releases from anthropogenic sources in China. When deposited to terrestrial ecosystems, Hg has a high affinity for natural organic carbon. This means that Hg concentrations will vary naturally as a function of the total organic carbon (TOC) content of different soils and sediment. Thus, Hg to TOC ratios in topsoil and surface sediment provides a useful normalized tracer of the anthropogenic impact on Hg contamination. We compiled literature-documented Hg and total organic carbon (TOC) data for topsoil (n = 957) and surface sediment (n = 1142) in China. Topsoil samples (n = 100) were also collected in this study to broaden the spatial coverage. We found large differences in Hg:TOC ratios among topsoil from background sites, agricultural and urban areas, and mining sites and surface sediment from fluvial, coastal, and marine environments. Specifically, a significant increase in Hg:TOC ratios occurred between soils from background sites (median: Hg:TOC = 21.1; Inter-Quartile Range (IQR): 9.67 to 40.7) and agricultural areas (median: 34.1; IQR: 22.1 to 58.7), urban areas (median: 62.1 ng g^-1; IQR: 34.2 to 154) and mining sites (median: 2780; range: 181 to 43500). Urban and mining sites show the largest increase in Hg:TOC ratios, reflecting elevated anthropogenic Hg inputs in these areas. Fluvial sediment showed higher Hg:TOC ratios (median: 197; IQR: 109 to 389) than coastal (median: 88.3; IQR: 46.8 to 168) and marine sediment (median: 89.7; IQR: 53 to 138), indicating decreased anthropogenic Hg input from rivers to coastal and marine regions. Results of our study suggest Hg:TOC ratios are a useful normalized indicator of the influence of anthropogenic Hg releases on Hg enrichment in topsoil and surface sediment.

Responses of the grass Paspalum distichum L. to Hg stress: A proteomic study

Paspalum distichum L. was tested to evaluate its ability to phytoremediate mercury (Hg) contaminated soil over a 60-d period by analysis of the total Hg concentrations in roots and leaves. Hg concentration in Hg-contamination soil decreased by 70.0 μg g^-1 after 60 day of grass cultivation and Hg was readily taken up by the roots (4.51 ± 1.90 μg g^-1) rather than the leaves (0.35 ± 0.02 μg g^-1). In addition, a comparative proteomic study was performed to unravel the protein expression involved in the Hg stress response in P. distichum L. A total of 49 proteins were classified as differentially proteins in the roots by the 'top three' proteomic analysis, of which 32 were up-regulated and 17 down-regulated in response to Hg stress. These changed proteins were classified by gene ontology analysis into five complex molecular functions involving photosynthesis and energy metabolism (31%), oxidative stress (14%), protein folding (16%), sulfur compound metabolism (10%), metal binding, and ion transport (29%). Moreover, the protein expression patterns were consistent with the metabolism pathway results. Overall, the results contribute to our understanding of the molecular mechanisms of the Hg response in P. distichum and we propose a theoretical basis for the phytoremediation of Hg-contaminated soils.

Total mercury, chromium, nickel and other trace chemical element contents in soils at an old cinnabar mine site (Merník, Slovakia): anthropogenic versus natural sources of soil contamination

The aims of this study were to investigate the occurrence and distribution of total mercury (Hg) and other trace elements of environmental concern, such as arsenic (As), copper (Cu), chromium (Cr), manganese (Mn), nickel (Ni), lead (Pb), zinc (Zn) and vanadium (V), in soils from the abandoned Merník cinnabar mine in eastern Slovakia. For this purpose, thirty soil samples from two depth intervals within the mine area (n = 60 soil samples) and additional sixteen soil samples from adjacent areas (n = 25 soil samples) were collected. Total Hg was measured by atomic absorption spectrometry, while As and other metals were analyzed using inductively coupled plasma atomic emission spectrometry. High mercury concentrations (> 100 mg/kg with a maximum of 951 mg/kg) were observed only in surface soils close to mine waste heaps and adits. Otherwise, Hg concentrations in the majority of surface soils were lower (0.14-19.7 mg/kg), however, higher than Hg in soils collected from sites outside the mine area (0.19-6.92 mg/kg) and even considerably higher than Hg in soils at sites not influenced by the Merník mine. Elevated Cr and Ni concentrations in soils regardless of their sampling sites (mean of 276 mg/kg and median of 132 mg/kg for Cr and 168 mg/kg and 81 mg/kg for Ni, respectively) were attributed to the lithology of the area; the soils are underlain by the sediments of the Central Carpathian Palaeogene, containing a detritus of ultrabasic rocks. As our geochemical data are compositional in nature, they were further treated by compositional data analysis (CoDA). Robust principal component analysis (RPCA) applied on centred (clr) log-ratio-transformed data and correlation analysis of compositional parts based on symmetric balances distinguished very well different sources of origin for the chemical elements. The following three element associations were identified: Hg association with the main source in mining/roasting, Cr-Ni association derived from bedrock and As-Cu-Mn-Pb-Zn-V association (natural background and minor sulphides/sulfosalts in mineralized rocks). The values of geoaccumulation index and enrichment factor suggested that concentrations of Hg in the soils were influenced by human industrial activities.

Mercury in soil, vegetable and human hair in a typical mining area in China: Implication for human exposure

Concentrations of total mercury (T-Hg) and methylmercury (MeHg) in soil, vegetables, and human hair were measured in a mercury mining area in central China. T-Hg and MeHg concentrations in soil ranged from 1.53 to 1054.97mg/kg and 0.88 to 46.52μg/kg, respectively. T-Hg concentrations was correlated with total organic carbon (TOC) content (R²=0.50, p<0.01) and pH values (R²=0.21, p<0.05). A significant linear relationship was observed between MeHg concentrations and the abundance of sulfate-reducing bacteria (SRB) (R²=0.39, p<0.05) in soil. Soil incubation experiments amended with specific microbial stimulants and inhibitors showed that Hg methylation was derived from SRB activity. T-Hg and MeHg concentrations in vegetables were 24.79-781.02μg/kg and 0.01-0.18μg/kg, respectively; levels in the edible parts were significantly higher than in the roots (T-Hg: p<0.05; MeHg: p<0.01). Hg species concentrations in rhizosphere soil were positively correlated to those in vegetables (p<0.01), indicating that soil was an important source of Hg in vegetables. Risk assessment indicated that the consumption of vegetables could result in higher probable daily intake (PDI) of T-Hg than the provisional tolerable daily intake (PTDI) for both adults and children. In contrast, the PDI of MeHg was lower than the reference dose. T-Hg and MeHg concentrations in hair samples ranged from 1.57 to 12.61mg/kg and 0.04 to 0.94mg/kg, respectively, and MeHg concentration in hair positively related to PDI of MeHg via vegetable consumption (R²=0.39, p<0.05), suggesting that vegetable may pose health risk to local residents.

Concentration of heavy metals in vegetables and potential health risk assessment in China

Food safety is an important issue in the world. This study assessed the health risk for the Chinese public when consuming vegetables grown in China, based on 1335 data records from 220 published papers during 2007-2016. The results showed that the average of Pb, Cd, and Hg concentration in vegetables was 0.106, 0.041, and 0.008 mg/kg, which were lower than the maximum allowable concentrations, respectively. Leaf vegetables contained higher heavy metals than root vegetables and fruit vegetables. On a provincial scale, the highest Pb, Cd, and Hg concentrations in vegetables were determined by those in soil and atmosphere. The total health risk index showed that people in Guizhou, Yunnan, Guangxi, Hunan, Guangdong, Hubei provinces in southern China, and Liaoning Province in northeast China, faced a high risk of Pb, Cd, and Hg when consuming vegetables.

Environmental assessment of mining industry solid pollution in the mercurial district of Azzaba, northeast Algeria

To date, there have been few detailed studies regarding the impact of mining and metallogenic activities on solid fractions in the Azzaba mercurial district (northeast Algeria) despite its importance and global similarity with large Hg mines. To assess the degree, distribution, and sources of pollution, a physical inventory of apparent pollution was developed, and several samples of mining waste, process waste, sediment, and soil were collected on regional and local scales to determine the concentration of Hg and other metals according to their existing mineralogical association. Several physico-chemical parameters that are known to influence the pollution distribution are realized. The extremely high concentrations of all metals exceed all norms and predominantly characterize the metallurgic and mining areas; the metal concentrations significantly decrease at significant low distances from these sources. The geo-accumulation index, which is the most realistic assessment method, demonstrates that soils and sediments near waste dumps and abandoned Hg mines are extremely polluted by all analyzed metals. The pollution by these metals decreases significantly with distance, which indicates a limited dispersion. The results of a clustering analysis and an integrated pollution index suggest that waste dumps, which are composed of calcine and condensation wastes, are the main source of pollution. Correlations and principal component analysis reveal the important role of hosting carbonate rocks in limiting pollution and differentiating calcine wastes from condensation waste, which has an extremely high Hg concentration (˃1 %).

Chemical Forms of Mercury in Human Hair Reveal Sources of Exposure

Humans are contaminated by mercury in different forms from different sources. In practice, contamination by methylmercury from fish consumption is assessed by measuring hair mercury concentration, whereas exposure to elemental and inorganic mercury from other sources is tested by analysis of blood or urine. Here, we show that diverse sources of hair mercury at concentrations as low as 0.5 ppm can be individually identified by specific coordination to C, N, and S ligands with high energy-resolution X-ray absorption spectroscopy. Methylmercury from seafood, ethylmercury used as a bactericide, inorganic mercury from dental amalgams, and exogenously derived atmospheric mercury bind in distinctive intermolecular configurations to hair proteins, as supported by molecular modeling. A mercury spike located by X-ray nanofluorescence on one hair strand could even be dated to removal of a single dental amalgam. Chemical forms of other known or putative toxic metals in human tissues could be identified by this approach with potential broader applications to forensic, energy, and materials science.

Mercury Release to Aquatic Environments from Anthropogenic Sources in China from 2001 to 2012

Based on an analysis of measured data and distribution factors, we developed the China Aquatic Mercury Release (CAMR) model, which we used to calculate an inventory of mercury (Hg) that was released to aquatic environments from primary anthropogenic sources in China. We estimated a total release of 98 tons of Hg in 2012, including coal-fired power plants (17%), nonferrous metal smelting (33%), coal mining and washing (25%), domestic sewage (17%), and other sectors (8.3%). The total primary anthropogenic Hg released to aquatic environments in China decreased at an annual average rate of 1.7% between 2001 and 2012, even though GDP grew at an annual average rate of 10% during this period. In addition to the Hg that was released to aquatic environments in China's provinces, we estimated the Hg release amounts and intensities (in g/km(2)·yr) for China's 58 secondary river basins. The highest aquatic Hg release intensities in China were associated with industrial wastewater on the North China Plain and domestic sewage in eastern China and southern China. We found that the overall uncertainty of our inventory ranges from -22% to 32%. We suggest that the inventory provided by this study can help establish a more accurate map of regional and global Hg cycling; it also has implications for water quality management in China.

The redox processes in Hg-contaminated soils from Descoberto (Minas Gerais, Brazil): implications for the mercury cycle

Investigations of the redox process and chemical speciation of Hg(II) lead to a better understanding of biogeochemical processes controlling the transformation of Hg(II) into toxic and bioaccumulative monomethyl mercury, mainly in areas contaminated with Hg(0). This study investigates the speciation and redox processes of Hg in soil samples from a small area contaminated with Hg(0) as a result of gold mining activities in the rural municipality of Descoberto (Minas Gerais, Brazil). Soil samples were prepared by adding Hg(0) and HgCl2 separately to dry soil, and the Hg redox process was monitored using thermodesorption coupled to atomic absorption spectrometry. A portion of the Hg(0) added was volatilized (up to 37.4±2.0%) or oxidized (from 36±7% to 88±16%). A correlation with Mn suggests that this oxidation is favored, but many other factors must be evaluated, such as the presence of microorganisms and the types of organic matter present. The interaction of Hg with the matrix is suggested to involve Hg(II)-complexes formed with inorganic and organic sulfur ligands and/or nonspecific adsorption onto oxides of Fe, Al and/or Mn. The kinetics of the oxidation reaction was approximated for two first-order reactions; the faster reaction was attributed to the oxidation of Hg(0)/Hg(I), and the slower reaction corresponded to Hg(I)/Hg(II). The second stage was 43-139 times slower than the first. The samples spiked with Hg(II) showed low volatilization and a shifting of the signal of Hg(II) to lower temperatures. These results show that the extent, rate and type of redox process can be adverse in soils. Descoberto can serve as an example for areas contaminated with Hg(0).

Health risk and significance of mercury in the environment

Mercury (Hg) has long been recognised as a global pollutant, because it can remain in the atmosphere for more than 1 year. The mercury that enters the environment is generally acknowledged to have two sources: natural and anthropogenic. Hg takes three major forms in the environment, namely methyl-Hg (MeHg), Hg(0) and Hg(2+). All three forms of Hg adversely affect the natural environment and pose a risk to human health. In particular, they may damage the human central nervous system, leading to cardiovascular, respiratory and other diseases. MeHg is bioavailable and can be bioaccumulated within food webs. Therefore, several methods of eliminating Hg from the soil and the aquatic system have been proposed. The focus of this article is on phytoremediation, as this technique provides a low-cost and environmentally friendly alternative to traditional methods.

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.

Mercury speciation and mobility in mine wastes from mercury mines in China

Mercury (Hg) speciation and mobility were determined in calcines and waste rocks collected from 9 Hg mines in China. Total Hg (THg) concentrations in the mine wastes varied widely in different Hg mines (with a range of 0.369 to 2,620 mg kg(-1)). Cinnabar is the dominant form of Hg in the mine wastes. However, Hg(2+) and Hg(0) concentrations in the calcines were significantly higher than these in the waste rocks, which suggested the retorting can produce large amounts of by-product Hg compounds. The THg and Hg(0) concentrations in certain mine wastes exceeded soil guidelines recommended by US Environmental Protection Agency; while total soluble Hg concentrations of leachates in certain mine wastes exceeded National Surface Water Quality Standard of China. Mine wastes are important Hg pollution sources to the aquatic ecosystem and atmosphere.

Structural change of human hair induced by mercury exposure

Mercury is one of the most hazardous pollutants in the environment. In this paper, the structural change of human hair induced by mercury exposure was studied. Human hair samples were, respectively, collected from the normal Beijing area and the Hg-contaminated Wanshan area of the Guizhou Province, China. Inductively coupled plasma mass spectroscopy was used to detect the element contents. A small angle X-ray scattering technique was used to probe the structural change. Three reflections with 8.8, 6.7, and 4.5 nm spacing were compared between the normal and the Hg-contaminated hair samples. The results confirm that the 4.5 nm reflection is from the ordered fibrillar structure of glycosaminoglycan (GAG) in proteoglycan (PG) that composes the matrix around the intermediate filaments. The increase of Ca content makes the regular oriented fibrillar structure of GAG transform to a random oriented one, broadening the angular extent of the reflection with 4.5 nm spacing. However, overdose Hg makes the core proteins where the ordered fibrils of GAG are attached become coiled, which destroys the ordered arrangements of fibrillar GAG in PG, resulting in the disappearance of the reflections with 4.5 nm spacing. The disappearance of the 4.5 nm reflection can be used as a bioindicator of overdose Hg contamination to the human body. A supercoiled-coil model of hair nanoscale structure and a possible mechanism of mercury effect in human hair are proposed in this paper.

Socioeconomic drivers of mercury emissions in China from 1992 to 2007

Mercury emissions in China have increased by 164% during 1992-2007. While major mercury producers were among energy combustion and nonferrous metal sectors, little is known for the socioeconomic factors driving the growth of emissions. In this paper we examine the underlying drivers and their contributions to the change of mercury emissions. Results show that changes in per capita GDP and GDP composition led to increased emissions which offset the reduction of emissions made possible by technology-induced decrease of mercury emissions intensity and changes in final demand mix. In particular, changes in final demand mix caused decreasing mercury emissions from 1992 to 2002 and increasing emissions from 2002 to 2007. Formation of fixed capital was the dominant driver behind the increase of mercury emissions, followed by the increasing urban population and net exports. This systems-based examination of socioeconomic drivers for China's mercury emission increase is critical for emission control by guiding policy-making and targets of technology development.

Mercury in the atmospheric and coastal environments of Mexico

In Mexico, published studies relating to the occurrence of Hg in the environment are limited. Among the main sources of Hg in Mexico are mining and refining of Auand Hg, chloralkali plants, Cu smelting, residential combustion of wood, carbo electric plants, and oil refineries. Hg levels are highly variable in the atmospheric compartment because of the atmospheric dynamics and ongoing metal exchange with the terrestrial surface. In atmospheric studies, Hg levels are usually reported as total gaseous Hg (TGM). In Mexico, TGM values ranged from 1.32 ng m-3 in Hidalgo state (a rural agricultural area) to 71.82 ng m-3 in Zacatecas state (an area where brick manufacturers use mining wastes as a raw material).Published information on mercury levels in the coastal environment comprise 21 studies, representing 21 areas, in which sediments constituted the substrate that was analyzed for Hg. In addition, water samples were analyzed for Hg in nine studies.Few studies exist on Hg levels in the Caribbean and in the southwest of the country where tourism is rapidly increasing. Hence, there is a need for establishing baseline levels of mercury in these increasingly visited areas. In regions where studies have been undertaken, Hg levels in sediments were highly variable. Variations in Hg sediment levels mainly result from geological factors and the varying degree of anthropogenic impacts in the studied areas. In areas that still have pristine or nearly pristine environments (e.g., coast, Baja California, Todos Santos Bay, and La Paz lagoon), sediment Hg levels ranged from <0.006 to 0.35 j.lg g-1 on a dry wt basis.When higher levels exist (0.34-57.94 j.lg g-1 on a dry wt basis), the environment generally shows the influence of inputs from mining, oil processing, agriculture,geothermal events, or harmful algal bloom events (e.g., Guaymas Bay and Coatzacoalcos estuary). From chronological studies performed in selected coastal lagoons in NW Mexico, it is clear that Hg fluxes to sediments have increased from2- to 15-fold in recent years. Since the 1940s, historical increases of Hg fluxes have resulted from higher agricultural waste releases and exhaust from the thermo electric plants. The levels of Hg in water reveal a moderate to elevated contamination of some Mexican coastal sites. In Urias lagoon (NW Mexico), moderate to high levels were found in the dissolved and suspended fraction, and these are related to shipping, the fishing industry, domestic effluents, and the presence of a thermoelectric plant. In Coatzacoalcos (SE Mexico), extremely elevated Hg levels were found during the decade of the 1970s. Low to moderate levels of Hg were measured in waters from the Alvarado lagoon (SE Mexico); those concentrations appear to be associated with river waters that became enriched with organic matter and suspended solids inthe brackish mixing zone.Regarding the Hg content in invertebrates, the use of bivalves (oysters and mussels)as biomonitors must be established along the coastal zones of Mexico, because some coastal lagoons have not been previously monitored. In addition, more research is needed to investigate shrimp farms that are associated with agricultural basins and receive effluents from several anthropogenic sources (e.g., mining activity and urban discharges). Hg residues in several vertebrate groups collected in Mexico have been studied.These include mammals, birds, reptiles, and fish. In elasmobranch species, the highest Hg concentration (27.2 flg g-1 dry wt) was found in the muscle of the smooth hammer head shark (Sphyrna zygaena). Teleost fish are the vertebrate group that has been most studied, with regard to Hg residue content; the highest value (5.67 11g g-1dry wt) was detected in the striped marlin (T. audax). Among reptiles, only marine turtles were studied; Hg levels found ranged from 0.795 in the liver to 0.0006flg g-1dry wt in the blood of L. olivacea. In birds, the highest Hg concentration (5.08 flg g-1dry wt) detected was in the liver of the olivaceous cormorant (P. olivaceous).Specimens from stranded marine mammals were also analyzed; levels of Hg ranged from 70.35 flg g-1 dry wt in the liver of stranded spinner dolphin (S. longirostris ), to0.145 flg g-1 dry wt in the muscle of gray whale (E. robustus). The presence of Hgin these marine animals is not thought to have caused the stranding of the animals.Other organisms like macroalgae and vestimentiferan tube worms were used to monitor the occurrence of Hg in the aquatic environment; levels were comparable to data reported on similar organisms from other areas of the world. Few investigation shave been carried out concerning the mercury content in human organs/tissues in Mexico. Considering the potential deleterious effects of Hg on kidney, lung, and the central nervous system, more information about human exposure to organic and inorganic forms of mercury and their effects is needed, both in Mexico and elsewhere.