Biogeochemistry Of Mercury, Selenium And Zinc In Chilly And Arid Region And Ecological Risk Assessment

Heavy metal pollution has been a major environmental problem, because of the nature of long-term, concealment, accumulation and enrichment through the food chain. The lakes in Inner Mongolia have been disturbed by different factors, because of the fragility of ecological system and human unreasonable use and interference. It has important theoretical and practical significance to investigate the heavy metals biogeochemistry of lakes in Inner Mongolia and it is helpful to guide the lake ecosystem management.Wuliangsuhai and Dalinuoer are the typical lake in chilly and arid regions of Inner Mongolia. Both lakes are important fishery farm and bird habitat in Inner Mongolia. Mercury, selenium and zinc were selected as the research object, and the levels, distribution and bioaccumulation of these three elements will be investigated in the two lake sediment-biotic systems, to elucidate its characteristics of environmental biogeochemistry. The tissue residue approach will be used to assess the ecological risk of metals to aquatic organisms.In addition, we also analyzed the content of Hg, Se and Zn in muscle of four fishes from aquatic product market in Ulaanbaatar of Mongolia and evaluate the human health risk by consum the fish. The major conclusions are as following.1. The average contents of total selenium in sediments from Wuliangsuhai and Dalinuoer were 0.310 mg/kg and 0.184 mg/kg, respectively, and have strong spatial differentiation. Sulphide combination state is the dominant speciation of Se in the sediment of two lakes, and the percents in total selenium from Wuliangsuhai andDalinuoer are 57.6% and 34.83%, respectively.The results of hazard quotients method showed that the sites indicating a medium risk ofselenium in the surface sediment of Wuliangsuhai and Dalinuoer account for 47% and 30%, respectively. Considering the bioaccumulation of selenium, its potential ecological risk in the two lakes should be pay more attention.2. The distribution of mercury and selenium in fish tissues with different feeding habitfrom two lakes are different. The order of content of Hg in fishes is warburg’s jarraud fish> snake head fish> crucian carp. The average contents of Hg in these three kinds of fishes are less than the values regulated in "pollution-free food of poisonous and harmful material set limit to of aquatic products (NY5073-2006)" and "standard of national food safety in food contaminants limited (GB2762-2012)". The tissue residue toxicity reference value of the whole body mercury and selenium were used as the basis for ecological risk. Low to moderate ecological risk were indicated for two lakes, and the risk of high trophic level species is higher than that of other species.3. Single factor pollution index method was applied to assess the ecological risk of zinc in fishes from Wuliangsuhai and Dalinuoer Lake, and the results were compared with this in Baiyangdian, East Taihu and Meiliang Bay, based on zinc content in fish muscle and food limited standard value of zinc for health. High levels of pollution were observed in crucian carp (Carassius auratus) from Wuliangsuahi, Leuciscus waleckii from Dalinuoer, the most muscles and all eggs of crucian carp from Baiyangdian, part of silver carp (Hypophthalmichthysmolitrix) from Meiliang Bay. Light to moderate pollution levels were observed in the snakehead (Channa argus) from Wuliangsuhai, Leuciscus waleckiifrom Dalinuoer, yellow catfish, silver carp, catfish, and crayfish from Baiyangdian, all fish from East Taihu and Meiliang Bay.4. Concentrations of Hg, Se and Zn in fish muscles ranged from 0.034 to 0.681 mg/kg, from 0.140 to 0.308 mg/kg and from 4.396 to 8.333 mg/kg, respectively. The levels of Hg, Se and Zn in muscles of burbot(Lota lota) was the highest, and the level of Hg in burbot exceeded the standard level in Safety Qualification for AgricultureProduct-Safety Requirements for Non-Environmental Pollution Aquatic Products. The THQs and total THQs based on fish consumption for Hg, Se and Zn were less than 1, and it indicated low risk for health. The estimated weekly intake values for Hg and Zn were also less than the provisional tolerable weekly intake value suggested by WHO. Considering the bioaccumulation and biomagnification potential of Hg, more attention should be paid to intake and health risk of Hg for citizen in Ulaanbaatar.The results of this study provides the basis for indicating biogeochemical behavior of mercury, selenium and zinc in lakes in Inner Mongolia and assessing the lakes safety.