Guangle Qiu

Mercury pollution in Asia: a review of the contaminated sites.

This article describes the mercury contaminated sites in Asia. Among the various regions, Asia has become the largest contributor of anthropogenic atmospheric mercury (Hg), responsible for over half of the global emission. Based on different emission source categories, the mercury contaminated sites in Asia were divided into various types, such as Hg pollution from Hg mining, gold mining, chemical industry, metal smelting, coal combustion, metropolitan cities, natural resources and agricultural sources. By the review of a large number of studies, serious Hg pollutions to the local environment were found in the area influenced by chemical industry, mercury mining and gold mining. With the probable effects of a unique combination of climatic (e.g. subtropical climate), environmental (e.g. acid rain), economic (e.g. swift growth) and social factors (e.g. high population density), more effort is still needed to understand the biogeochemistry cycle of Hg and associated health effects in Asia. Safer alternatives and cleaner technologies must be developed and effectively implemented to reduce mercury emission; remedial techniques are also required to restore the historical mercury pollution in Asia.

In Inland China, Rice, Rather than Fish, Is the Major Pathway for Methylmercury Exposure

Background Fish consumption is considered the primary pathway of methylmercury (MeHg) exposure for most people in the world. However, in the inland regions of China, most of the residents eat little fish, but they live in areas where a significant amount of mercury (Hg) is present in the environment. Objectives We assessed concentrations of total Hg and MeHg in samples of water, air, agricultural products, and other exposure media to determine the main exposure pathway of Hg in populations in inland China. Methods We selected Guizhou Province for our study because it is highly contaminated with Hg and therefore is representative of other Hg-contaminated areas in China. We selected four study locations in Guizhou Province: three that represent typical environments with severe Hg pollution [due to Hg mining and smelting (Wanshan), traditional zinc smelting (recently closed; Weining), and heavy coal-based industry (Qingzhen)], and a village in a remote nature reserve (Leigong). Results The probable daily intake (PDI) of MeHg for an adult population based on 60 kg body weight (bw) was considerably higher in Wanshan than in the other three locations. With an average PDI of 0.096 μg/kg bw/day (range, 0.015–0.45 μg/kg bw/day), approximately 34% of the inhabitants in Wanshan exceeded the reference dose of 0.1 μg/kg bw/day established by the U.S. Environmental Protection Agency. The PDI of MeHg for residents in the three other locations were all well below 0.1 μg/kg bw/day (averages from 0.017 to 0.023 μg/kg bw/day, with a maximum of 0.095 μg/kg bw/day). In all four areas, rice consumption accounted for 94–96% of the PDI of MeHg. Conclusion We found that rice consumption is by far the most important MeHg exposure route; however, most of the residents (except those in Hg-mining areas) have low PDIs of MeHg.

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.

Methylmercury Exposure and Health Effects from Rice and Fish Consumption: A Review

Methylmercury (MeHg) is highly toxic, and its principal target tissue in humans is the nervous system, which has made MeHg intoxication a public health concern for many decades. The general population is primarily exposed to MeHg through consumption of contaminated fish and marine mammals, but recent studies have reported high levels of MeHg in rice and confirmed that in China the main human exposure to MeHg is related to frequent rice consumption in mercury (Hg) polluted areas. This article reviews the progress in the research on MeHg accumulation in rice, human exposure and health effects, and nutrient and co-contaminant interactions. Compared with fish, rice is of poor nutritional quality and lacks specific micronutrients identified as having health benefits (e.g., n-3 long chain polyunsaturated fatty acid, selenium, essential amino acids). The effects of these nutrients on the toxicity of MeHg should be better addressed in future epidemiologic and clinical studies. More emphasis should be given to assessing the health effects of low level MeHg exposure in the long term, with appropriate recommendations, as needed, to reduce MeHg exposure in the rice-eating population.

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.

The Process of Methylmercury Accumulation in Rice (Oryza sativa L.)

Recent studies have shown that rice consumption can be an important pathway of methylmercury (MeHg) exposure to humans in Hg mining areas and also in certain inland areas of Southwestern China. The seed of rice has the highest ability to accumulate MeHg compared to other tissues. The main objective of this study was to investigate the process of (MeHg) accumulation in rice seed (Oryza sativa L.) by monitoring MeHg levels in specific tissues of rice plants experiencing various levels of Hg multisource pollution during a full rice growing season. Four groups of experimental plantations were utilized, distributed among a rural artisanal Hg production site and a regional background control site. Our results suggest that the newly deposited Hg is more readily transformed to MeHg and accumulated in rice plants than Hg forms with an extended residence time in soil, and soil is the potential source of MeHg in the tissues of rice plants. MeHg in soil was first absorbed by roots and then translocated to the above-ground parts (leaf and stalk). During the full rice growing season only a very small amount of MeHg was retained in the root section. In the premature plant, the majority of MeHg is located in the leaf and stalk; however, most of this MeHg was transferred to seed during the ripening period.

Tracing Mercury Contamination Sources in Sediments Using Mercury Isotope Compositions

Mercury (Hg) isotope ratios were determined in two sediment cores collected from two adjacent reservoirs in Guizhou, China, including Hongfeng Reservoir and Baihua Reservoir. Hg isotope compositions were also analyzed in a soil sample collected from the catchment of Hongfeng Reservoir and three cinnabar samples collected from the Wanshan Hg mine. Baihua Reservoir was contaminated with runoff from Guizhou Organic Chemical Plant (GOCP) when metallic Hg was used as a catalyst to produce acetic acid. Hongfeng Reservoir, located upstream of Baihua, receives Hg from runoff and atmospheric deposition. We demonstrated that delta(202)Hg values relative to NIST 3133 of sediment in Baihua Reservoir ranging from -0.60 to -1.10 per thousand were distinctively different from those in Hongfeng Reservoir varying from -1.67 to -2.02 per thousand. While sediments from both Baihua and Hongfeng Reservoirs were characterized by mass dependent variation (MDF), only Hongfeng Reservoir sediments were characterized by mass independent variation (MIF). Moreover, by using a binary mixing model, we demonstrated the major source of Hg in sediment of Hongfeng Reservoir was from runoff due to soil erosion, which was consistent with the conclusion obtained from a previous Hg balance study. This study demonstrates Hg isotope data are valuable tracers for determining Hg contamination sources in sediments.

Allocation and source attribution of lead and cadmium in maize (Zea mays L.) impacted by smelting emissions.

Plants grown in contaminated areas may accumulate trace metals to a toxic level via their roots and/or leaves. In the present study, we investigated the distribution and sources of Pb and Cd in maize plants (Zea mays L.) grown in a typical zinc smelting impacted area of southwestern China. Results showed that the smelting activities caused significantly elevated concentrations of Pb and Cd in the surrounding soils and maize plants. Pb isotope data revealed that the foliar uptake of atmospheric Pb was the dominant pathway for Pb to the leaf and grain tissues of maize, while Pb in the stalk and root tissues was mainly derived from root uptake. The ratio of Pb to Cd concentrations in the plants indicated that Cd had a different behavior from Pb, with most Cd in the maize plants coming from the soil via root uptake.

Mercury exposure in the population from Wuchuan mercury mining area, Guizhou, China

Mercury (Hg) exposure in the population from Wuchuan mercury mining area (WMMA), Guizhou, China, was evaluated by human hair Hg investigation. Total gaseous mercury (TGM) in the ambient air and Hg in rice were measured to assess human risk of Hg exposure. High TGM concentrations in the ambient air were found near smelting workshop. Rice not only contained high total mercury (T-Hg) which ranged from 6.0-113 ng/g, but also contained highly elevated methylmercury (Me-Hg) which ranged from 3.1-13.4 ng/g. The means of hair T-Hg concentrations were 33.9 microg/g and 21.5 microg/g at YQG and JXC sites, respectively. Residents from other sites also reflected a certain level of Hg exposure. Age had no significant effect on hair Hg levels, but male had higher hair T-Hg concentrations due to occupational exposure and also higher Me-Hg levels which might be related to larger amount of rice consumption. Hair may be a useful tool for monitoring human exposure of Hg vapor in Hg-mining areas. By a preliminary estimation, the inhalation of Hg polluted air was the main route of inorganic Hg exposure to the smelting workers and vicinal residents; but the population in the study area was also at a potential risk of Me-Hg exposure via rice intake.