| Along with the urbanized and modernized advancement quickening, mercury pollution caused by human activity has drawn wide public concern. Mercury as the sole heavy metal which can be able to complete cycle in the ecosystem, with the features of high volatility, easy to long distance transmission, and therefore threaten human health. In this study, the THg content in some surface soil samples, surface sediment samples, deep sediment samples of soils, inflow rivers and lakes, and the Hg fractionation in surface sdiments were determined, in order to analyze the spatial distribution, bio-availability, migration, and to make a comprehensive evaluation for mercury. The specific research and results were as follows.(1) The average content of Hg was 0.042mg/kg, which was higher 3.2 times than the mercury background value of soils in Shandong Province, and had strong ability of enrichment in suface soils of Nansi Lake. And the THg content of urban soil decreased in the order of Zaozhuang(0.049mg/kg)>Jining(0.047mg/kg)>Heze(0.036mg/kg). What?s more, the THg content in surface sediments and deep sediments of Nansi Lake were 0.046mg/kg and 0.029mg/kg,and they were more than 3.1 times and 1.9 times of background values, respectively. Comparing the THg content with the values of sediment quality criteria(SQGs), we can see that the THg content of all samples in Nansi Lake sediments lower than TEL. The degree of enrichment was in the order: Dushan Lake>Weishan Lake>Nanyang Lake>Zhaoyang Lake.(2) The distribution of THg in soils of Nansi Lake basin had obvious spatial gradient, it was mainly related to human activities intensity distribution. The high THg value was largely in the area of severe urban activities, while the THg content in agricultural area was relatively low. In addition, there was a certain difference in mercury content for various soil types, which may be associated with the forming environment and parent materials. The spatial distribution characteristics of THg content was high-low-high in surface sediments of Nansi Lake, and the THg levels decreased gradually from the estuary to lake district. This spatial distribution consistented with the surrounding soil pollution distribution.(3) The result of geochemical fractionation analysis showed that Hg existed mainly in the residual fraction of Nansi Lake sediments, with lower bio-availability. The proportion of various fractionation account for THg content was residual fraction(65.15%)>Humic acid fraction(23.40%)>strongly organic fraction(7.21%)> carbonate fraction(1.84%)> Fe/Mn oxide fraction(1.31%)>ion exchange fraction(0.89%)>water solution fraction(0.20%). Overall, the non-residual fraction had direct harm to the environment, and the non-residual fraction mercury content of Weishan Lake was the highest, with higher ecological hazards, Nanyang Lake was next, followed by Dushan Lake, Zhaoyang Lake.(4) According to the THg content of the Nansi Lake surface soils, inflow river surface sediments, surface sediments and deep sediments, it can be seen that mercury had obvious migration behavior at the soil-water-sediment interface. And the correlation analysis showed that pH, TOC, minerals and other heavy metals in soils and sediments could affect the mercury distribution and migration to a certain extent.(5) By combining with Igeo, RI and RSP to comprehensive evaluate the mercury pollution situation in Nansi Lake Basin. Based on the evaluation results of total mercury and fractionation, indicating that Hg in the surface soils of Nansi Lake Basin was in slightly pollution, with slight ecological risk. While the whole Nansi Lake was in moderate pollution, it had little direct effect to the environment due to the non-residual fraction accounted for 51% of residual fraction. Moreover, the potential ecological risks of Hg pollution should be seriously concerned. |
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