三峡库区消落带土壤汞形态分布与风险评价

Distribution and Risk Assessment of Mercury Species in Soil of the Water-LevelFluctuating Zone in the Three Gorges Reservoir

为了解三峡库区消落带土壤中汞污染现状和环境风险，选择重庆14个区县的消落带，采集了192个土壤样品，分析其土壤总汞和汞形态分布，探讨其生物可利用性，对比研究和评估土壤总汞与汞赋存形态的污染水平和生态风险．结果表明，三峡库区消落带土壤中汞含量差异较大，土壤汞含量为22．4-393．5μg·kg^-1，平均值为（84．2±54．3）斗g·kg^-1，76．6％的采样点土壤汞含量超过了三峡库区土壤汞背景值．土壤中的汞以残留态为主，不同汞形态所占比例为：水溶态汞4．1％、酸溶态15．5％、碱溶态汞18．3％、过氧化氢溶态汞10．9％、残留态汞51．3％．各区县土壤中生物可利用性汞（水溶态汞、酸溶态汞与碱溶态汞之和）平均含量为19．7-36．6μg·kg^-1，生物可利用态汞占总汞的比例达到22．1％-51．6％．地累积指数和潜在生态危害指数评价结果均表明，三峡库区消落带土壤中汞赋存形态的污染水平和生态风险都较低，由生物可利用态汞带来的牛态风险也很小；而对土壤总汞含量评价的结果明显偏大．因此，采用汞赋存形态进行污染现状和生态危害评价更能反映消落带土壤汞的环境风险．

To investigate pollution level and ecological risk of mercury in soils of the water-level-fluctuating zone in the Three Gorges Reservoir Region, 192 surface soil samples from 14 counties （districts） in Chongqing were obtained. Concentrations of THg and Hg species, bioavailable Hg were analyzed and discussed. Geoaccumulation index （Igeo） and Haikanson potential ecological risk index （ E ） were applied to assess the pollution status and potential ecological risk of THg and Hg species, respectively. The results showed that significant differences in the concentration of THg were found in soils of water-level-fluctuating zone in the Three Gorges Reservoir. The THg concentration ranged from 22.4 to 393.5 p,g. kg^-1, with an average of （ 84.2 ± 54.3 ） p,g. kg^-1. 76.6% of the samples＇ THg content was higher than the soil background value in the Three Gorges Reservoir Region. The percentage of five mercury species （water-soluble Hg, HCl-soluble Hg, KOH-soluble Hg, H202-soluble Hg, residue Hg） in soils were 4. 1%, 15.5%, 18.3%, 10.9% , 51.3% , respectively. The average concentrations of bioavailable mercury varied between 19.7- 36.6 μg.kg^-1 , and the percentage of bioavailable Hg was 22. 1% -51.6% of THg. According to the geoaccumulation index, the soils were lightly polluted by Hg. Halkanson single potential ecological risk index evaluation showed that Hg species had a low potential ecological risk, moreover, soils of water-level-fluctuating zone in the Three Gorges Reservoir were at low ecological risk levels as evaluated by bioavailable Hg. While, the assessment results based on THg of soils was much higher than that based on the Hg species. Two methods of evaluation showed that the lgoo and Er values calculated based on the Hg species better reflected the actual pollution levels of soils and its hazard to aquatic organisms.