Total mercury,methylmercury and selenium in mercury polluted areas in the province Guizhou,China

The province of Guizhou in Southwestern China is currently one of the world's most important mercury production areas. Emissions of mercury from the province to the global atmosphere have been estimated to be approximately 12% of the world total anthropogenic emissions. The main objective of this study was to assess the level of contamination with Hg in two geographical areas of Guizhou province. Mercury pollution in the areas concerned originates from mercury mining and ore processing in the area of Wanshan, while in the area of Quingzhen mercury pollution originates from the chemical industry discharging Hg through wastewaters and emissions to the atmosphere due to coal burning for electricity production. The results of this study confirmed high contamination with Hg in soil, sediments and rice in the Hg mining area in Wanshan. High levels of Hg in soil and rice were also found in the vicinity of the chemical plant in Quingzhen. The concentrations of Hg decreased with distance from the main sources of pollution considerably. The general conclusion is that Hg contamination in Wanshan is geographically more widespread, due to deposition and scavenging of Hg from contaminated air and deposition on land. In Quingzhen Hg contamination of soil is very high close to the chemical plant but the levels reach background concentrations at a distance of several km. Even though the major source of Hg in both areas is inorganic Hg, it was observed that active transformation of inorganic Hg to organic Hg species (MeHg) takes place in water, sediments and soils. The concentration of Hg in rice grains can reach up to 569 microg/kg of total Hg of which 145 microg/kg was in MeHg form. The percentage of Hg as MeHg varied from 5 to 83%. The concentrations of selenium can reach up to 16 mg/kg in soil and up to 1 mg/g in rice. A correlation exists between the concentration of Se in soil and rice, indicating that a portion of Se is bioavailable to plants. No correlation between Hg and Se in rice was found. Exposure of the local population to Hg may occur due to inhalation of Hg present in air (in particular in Hg mining area) and consumption of Hg contaminated food (in particular rice and fish) and water. Comparison of intake through these different routes showed that the values of Hg considerably exceed the USA EPA Reference Concentration (RfC) for chronic Hg exposure (RfC is 0.0004 mg/m(3)) close to the emission sources. Intake of Hg through food consumption, particularly rice and fish, is also an important route of Hg exposure in study area. In general, it can be concluded that the population mostly at risk is located in the vicinity of smelting facilities, mining activities and close to the waste disposal sites in the wider area of Wanshan. In order to assess the real level of contamination in the local population, it is recommended that biomonitoring should be performed, including Hg and MeHg measurements in hair, blood and urine samples.     

Impacts of mercury contaminated mining waste on soil quality, crops, bivalves, and fish in the Naboc River area, Mindanao, Philippines

Rice paddy fields in the Naboc area, near Monkayo on the island of Mindanao, Philippines, have been irrigated four times a year over the last decade using Naboc River water contaminated with mercury (Hg) by artisanal gold mining in the Diwalwal area. Silt containing up to at least 90 mg Hg/kg (d.w.) has been deposited in rice paddy fields during the 1990s and this has been repeatedly mixed into the rice root zone through ploughing. Hg in the rice paddy field soils averages 24 mg Hg/kg and generally exceeds the UK and Canadian soil quality thresholds for agricultural soils as well as the proposed Dutch Intervention value and the USEPA soil ingestion Soil Screening Level (SSL) for inorganic Hg. Much lower Hg concentrations (0.05-0.99 mg/kg) within the range expected for uncontaminated soils, characterise soils on which corn and bananas are cultivated, largely because these are not irrigated with Hg-contaminated water from the Naboc River. The estimated total weekly MeHg intake for a person living in the Naboc area related to the weekly consumption of 2.1 kg of rice grown on Hg-contaminated soils (15 microg MeHg) in conjunction with 1 kg of fish (220 microg MeHg) and 100 g of mussels (50 microg MeHg) from the Naboc River, would total 285 microg MeHg (equivalent to 4.75 microg/kg bw for a 60 kg adult), which is nearly three times the JECFA PTWI of 1.6 microg/kg bw. This will significantly contribute to the population mercury exposure and might explain why 38% of the local inhabitants were classified as Hg intoxicated during a mercury toxicity assessment [Drasch GS, B?se, O'Reilly S, Beinhoff C, Roider G, Maydl S. The Mt. Diwata study on the Philippines 1999-assessing mercury intoxication of the population by small scale gold mining. Sci Total Environ 2001; 267(1-3): 151-168.].     

Mercury distribution and speciation in water and fish from abandoned Hg mines in Wanshan, Guizhou province, China

Concentrations of total mercury (Hg^T), methylmercury (MeHg), and its speciation in water samples as well as fish collected from abandoned Hg mines in Wanshan, Guizhou province, China, were measured to show regional dispersion of Hg contaminations that are not well known. High Hg^T and MeHg^T (total methylmercury) concentrations obtained in waters from mining areas, ranged from 15 to 9300 ng/l and 0.31 to 25 ng/l, respectively. MeHg^T were not correlated with Hg^T, whereas, peak values in both cases were in accord with high concentrations of particulate fraction, which appeared to be enhanced during high-flow regime with ratios reaching to 99%. Elevated Hg concentrations in the particulate form indicated that particles released from Hg mining tailings (calcines) might be an important pathway of Hg to the aquatic system. The concentrations of total Hg in fish muscle were elevated ranging from 0.061 to 0.68 mg/kg, but MeHg were generally low ranging from 0.024 to 0.098 mg/kg with a mean ratio of 28%. The concentrations and distribution patterns of Hg in aquatic systems suggested derivation from historic Hg mining sites in the Wanshan area.     

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.     

A preliminary study on mercury contamination to the environment from artisanal zinc smelting using indigenous methods in Hezhang County, Guizhou, China: Part 2. Mercury contaminations to soil and crop

Artisanal zinc smelting using indigenous method in Hezhang County, Guizhou, China has posed seriously environmental pollution to the local environment. Within less than 150 km2 area in Hezhang, a few metric tons of mercury were released into the atmosphere each year since 1989 due to artisanal zinc smelting, and the surface waters were seriously contaminated with mercury. For the first time, we investigated the mercury contamination to the local soil and crop compartments due to mercury emissions from artisanal zinc smelting activities in this area. Mercury distribution patterns in 5 soil profiles collected in artisanal zinc smelting area showed that the top soils were seriously contaminated with mercury. The soils from agriculture land close to the zinc smelting areas were also contaminated with mercury due to the deposition of mercury species that emitted from artisanal zinc smelting processes. Total mercury concentrations in top soils decrease exponentially with distance from the zinc smelting area. Corn plants that were cultivated in agriculture land close to the zinc smelting area were also contaminated with mercury. Mercury concentration in corn plant tissue increased in the order of grains相似文献   

Effect of watershed parameters on mercury distribution in different environmental compartments in the Mobile Alabama River Basin, USA

Total mercury (THg) and mono-methylmercury (MeHg) levels in water, sediment, and largemouth bass (LMB) (Micropterus salmoides) were investigated at 52 sites draining contrasting land use/land cover and habitat types within the Mobile Alabama River Basin (MARB). Aqueous THg was positively associated with iron-rich suspended particles and highest in catchments impacted by agriculture. Sediment THg was positively associated with sediment organic mater and iron content, with the highest levels observed in smaller catchments influenced by wetlands, followed by those impacted by agriculture or mixed forest, agriculture, and wetlands. The lowest sediment THg levels were observed in main river channels, except for reaches impacted by coal mining. Sediment MeHg levels were a positive function of sediment THg and organic matter and aqueous nutrient levels. The highest levels occurred in agricultural catchments and those impacted by elevated sulfate levels associated with coal mining. Aqueous MeHg concentrations in main river channels were as high as those in smaller catchments impacted by agriculture or wetlands, suggesting these areas were sources to rivers. Elevated Hg levels in some LMB were observed across all types of land use and land cover, but factors such as shallow water depth, larger wetland catchment surface area, low aqueous potassium levels, and higher Chl a concentrations were associated with higher Hg burdens, particularly in the Coastal Plain province. It is suggested that the observed large variability in LMB Hg burdens is linked to fish displacement by anglers, differences in food web structure, and sediment biogeochemistry, with surficial sediment iron oxides buffering the flux of MeHg from sediments to deeper water pelagic food webs.     

Pilot study of intrauterine exposure to methylmercury in Eastern Aegean islands, Greece

A group of islands with a total population of about 200,000 was identified in the Eastern Aegean, where there was evidence to suggest possible increased exposure to methylmercury (MeHg) through consumption of fresh local fish and other seafood from seas bordered by mercury-bearing rock. A feasibility study was conducted to explore the possibility of defining a local population of mother-child pairs in whom to investigate the intrauterine exposure effect. Analysis of 246 hair samples collected from pregnant women and mothers of newborn babies and children under 5 years showed levels of total Hg from 0.046 microg/g to 17.5 microg/g, geometric mean 1.36 microg/g, and of MeHg from 0.031 microg/g to 16.2 microg/g, geometric mean 1.07 microg/g. About 5% of the mothers had hair total Hg levels in excess of 6.00 microg/g. Investigation of dietary habits showed that one-third of the mothers eat fresh local fish at least 3 times weekly, one-third once a week and 10% rarely or never. There was a close association between weekly rates of local fish consumption and hair levels of both total Hg and MeHg. A power calculation determined that a cohort of 3000 mother-child pairs would enable comparison of a high-exposure group (those with the upper 5% of hair MeHg) with a low exposure group (5%, selected from those with the lower 30% of hair MeHg, matched for confounding factors), in order to detect an effect size of 0.35 to 0.45 at a power of 85-95%. It is concluded that the mothers and children in the Eastern Aegean islands studied comprise a population suitable for an epidemiological study of the effects of intrauterine exposure to MeHg via maternal fresh local fish consumption.     

Strategies to lower methyl mercury concentrations in hydroelectric reservoirs and lakes: A review

Mercury (Hg) concentrations in fish in lakes are elevated due to increased global cycling of Hg. A special case of elevated Hg concentrations in fish occurs in new hydroelectric reservoirs because of increased rates of converting Hg in the environment into methyl mercury (MeHg). People and wildlife that eat fish from hydroelectric reservoirs have an elevated risk of accumulating too much MeHg. Demand for electrical energy is leading to the creation of new reservoirs. In 2005, Canada derived 60% of its electricity from hydroelectric reservoirs. As a result, hydroelectric companies and governing agencies are exploring strategies to lower MeHg contamination. Strategies may involve lowering the source of Hg before flooding, the rate of Hg methylation, or MeHg bioaccumulation and biomagnification. Possible strategies reviewed in this article include selecting a site to minimize impacts, intensive fishing, adding selenium, adding lime to acidic systems, burning before flooding, removing standing trees, adding phosphorus, demethylating MeHg by ultraviolet light, capping and dredging bottom sediment, aerating anoxic bottom sediment and waters, and water level management. A preventative strategy is to limit the flooded area, especially wetland areas. Flooded upland areas that contain less carbon produce MeHg for a shorter time than wetland areas. Run-of-the-river reservoirs contain lower MeHg concentrations than reservoirs that flood vast areas, at the cost of exporting MeHg downstream. Managing water levels to flush systems during times of peak MeHg production may have benefits for the reservoir, but also transports MeHg downstream. Intensive fishing can lower MeHg in food webs by increasing fish growth rate. Additions of selenium can lower MeHg bioaccumulation, but the mechanisms are not well established and excess selenium causes toxicity. Liming can lower fish Hg concentrations in lakes acidified with sulphuric and nitric acid. Burning before flooding can lower the production of MeHg, but MeHg bioaccumulation may increase. The most promising strategy will be one that is agreeable to all affected people.     

Mercury methylation along a lake-forest transect in the Tapajós river floodplain, Brazilian Amazon: seasonal and vertical variations

The seasonal and spatial variations of net methylmercury production in sediments, soils and other sites were evaluated by assays with 203Hg at different depths and locations along a lake-forest transect at lake Enseada Grande, Tapajós river. Soil and sediment samples were taken at the surface and at different depths up to 9 cm. Fresh samples and acidified controls (1-3 g dry wt.) were slurried with local water and incubated in the dark at 25-28 degrees C for 3 days with 0.5-1.6 microg Hg g(-1) (dry wt.) added as 203HgCl2. CH3 203Hg was extracted and measured in scintillation cocktail after acid leaching. Methylmercury production varied by orders of magnitude among sites and among sediment or soil layers. Seasonal variations were smaller than those with sample depth and location. In both seasons, MeHg formation in sediment and soil or flooded soil decreased with depth and was, in the top layers, one order of magnitude higher in the C-rich littoral macrophyte zone (2.3-8.9%) and flooded forest (3.2-4.5%) than in the center of the lake (0.2-0.56%). Similar MeHg production was found in slurried dry soils (dry season) and in soils already flooded for months. In the macrophyte zone soil (dry season), methylation was mainly associated with the thin Paspalum sp. rootlet layer. In the forest site, vertical variation in methylation was less pronounced in flooded than in dry soils and during the inundation the higher methylation rate was found in the flocculent sediment settled over the litter layer. The roots of floating Paspalum sp. were an important Hg methylation site, particularly those heavily colonized with periphyton (3.4-5.4%). Methylation in surface or near-bottom water was undetectable (< 3 x 10(-2)%) at all sites. Flooded forests and macrophyte mats are specific features of the Amazon and are important links between Hg inputs from natural and manmade sources and MeHg exposure of local populations through fish intake.     

The burning question: does burning before flooding lower methyl mercury production and bioaccumulation?

Production of methyl mercury (MeHg) is elevated in new hydroelectric reservoirs because organic carbon stimulates methylation of inorganic mercury (Hg) stored in the terrestrial system. This can cause adverse health in fish and in organisms that eat fish. We expected that burning vegetation before flooding would decrease the amount of Hg and organic carbon and thereby lower MeHg production. We conducted a replicated field experiment to investigate the effects of burning vegetation and soil before flooding on MeHg production and bioaccumulation. Vegetation and soil were added to mesocosms in the following combinations: unburned vegetation and unburned soil (Fresh treatments), burned vegetation and unburned soil (Partial Burn treatments), and burned vegetation and burned soil (Complete Burn treatments). Controls had no added vegetation or soil. During combustion with propane torches, a large percentage of the total Hg (THg) and MeHg was lost from vegetation and soil. THg and MeHg concentrations were highest in the surface water of Fresh treatments, lower in Partial Burn treatments and lowest in Complete Burn treatments and controls. Differences in concentrations of MeHg in biota were consistent among treatments, but did not follow aqueous concentrations. On the final sample date, MeHg concentrations in biota of Controls and Partial Burn treatments were greater than in Complete Burn and Fresh treatments. The lack of relationship between MeHg in biota and MeHg in water may have been due to modification of the bioavailability of MeHg by dissolved organic matter as the ratios of MeHg in biota to water were inversely correlated with concentrations of dissolved organic carbon. Although burning before flooding decreased MeHg concentrations in the water, it did not lower MeHg accumulation in the lower food web.