1. Rural Energy & Environment Agency, Ministry of Agriculture, Beijing 100125, China;
2. Agro-Environmental Protection Institute, Ministry of Agriculture, Tianjin 300191, China
The leaching characteristics of mercury (2mg/kg Hg spiked in soil) and their influencing factors in 22 Chinese soils under simulated rain (pH 5.6) through soil column experiments were investigated in this study. The results indicated that the Hg release process of the studied soils could be divided into 3 classes. Firstly, concentrations of Hg in soil leachates from class 1 during leaching process was very low, and less than Groundwater Quality Standard for Class Ⅲ (1μg/L), which included black soil from Jilin, chernozem from Jilin, felty soil from Tibet, paddy soil from Hunan, dark-brown soil from Jilin, yellow soil from Fujian, yellow soil from Jiangsu, chestnut soil from Inner Mongolia. Secondly, Hg in soil leachates from class 2 were comparatively low, less than Groundwater Quality Standard for Class Ⅲ in the early of leaching process (2~3L), then it increased significantly at the middle of leaching process, and decreased from 5~15μg/L down to below Groundwater Quality Standard for Class Ⅲ at the end of leaching process (5~6L), which included red soil from Guangxi, yellow soil from Guizhou, brown soil from Liaoning, sierozem from Gansu and loessal soil from Shanxi. Thirdly, The release mechanism of Hg in soils of class 3appears to be consisted of two phases involving the initial rapid process (leachate are less than 4L) followed by a slow continuous process (leachate exceeds 4L), which included the other 9soils (latosol from Henan, yellow-brown soil from Jiangsu, purple soil from Chongqing, cinnamon soil from Hebei, latosolic red soil from Guangxi, fluvo-aquic soil from Tianjin, salt-affected soil from Jilin, red soil from Jiangxi, brown desert soil from Xinjiang). It was also found that the cumulative release rates of Hg from studied soils were accounted for 0.33% (yellow soil from Guizhou)-5.95% (black soil from Jilin), on an average of 1.55%. Stepwise multiple regression analysis showed that release of Hg from soils might be related to soil organic matter (OM), pH, and soil total Hg (THg) (lnq=1.8+0.62lnTHg-0.109pH-0.918lnOM) These 3factors could describe 58.65% of the variability in Hg release from soils.
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