广西刁江流域土壤-水稻系统汞含量特征及其影响因素研究

为探究广西刁江流域沿岸农田土壤和水稻的汞污染状况，选取广西刁江流域沿岸农田土壤-水稻系统，采用地累积指数(I_geo)法进行土壤汞污染评价，研究该区域稻田土壤及水稻(Oryza sativa L.)植株的汞含量特征及影响因素。结果表明，研究区的耕层土壤汞平均含量为309 ng/g，有97.5%的土壤汞含量超过全国表层土壤汞背景值(87 ng/g)，有27.5%的土壤汞含量超过广西表层土壤汞背景值(225 ng/g)。地累积指数评价结果显示，研究区内80%的土壤处于无污染状态，但有个别点位的土壤汞污染较严重，仍需要注意进行环境监管。土壤各形态汞含量均值排序为残渣态>腐殖酸结合态>铁锰结合态>碳酸盐结合态>水溶态>离子交换态>强有机结合态，土壤汞的生物有效性较低。研究区稻米汞平均含量为6.08 ng/g，籽实汞超标率为6%，水稻植株根、叶、茎、壳、籽实汞含量之比约为13.5∶5.2∶1.7∶1.2∶1。稻米对土壤汞的富集系数平均值为0.031，富集能力较弱。相关性分析结果表明，土壤汞含量与稻米汞含量、土壤有机碳(Soil Organic Carbon,SOC)、pH值均无显著相关关系，稻米汞含量与SOC呈显著负相关关系。

Characteristics and Influencing Factors of Mercury in Soil-Rice System in Diaojiang River Basin,Guangxi

In order to explore the mercury pollution status of farmland soil and rice along the Diaojiang River Basin in Guangxi,the farmland soil-rice system along the Diaojiang River Basin in Guangxi was selected,and the soil mercury pollution was evaluated by the geo-accumulation index (I_geo) method.The characteristics and influencing factors of mercury content in paddy soil and rice (Oryza sativa L.) plants in the area were studied.The results showed that the average content of mercury in the plough layer soil of the study area was 309 ng/g,97.5% of the soil mercury content exceeded the national surface soil mercury background value (87 ng/g),and 27.5% of the soil mercury content exceeded the Guangxi surface soil mercury background value (225 ng/g).The evaluation results of geo-accumulation index showed that 80% of the soil in the study area was in a pollution-free state,but the soil mercury pollution at some points was serious,and environmental supervision was still needed.The average content of various forms of mercury in the soil was ranked as residual state>humic acid bound state>iron-manganese bound state>carbonate bound state>water soluble state>ion exchange state>strong organic bound state,and the bioavailability of mercury in soil was low.The average content of mercury in rice grain in the study area was 6.08 ng/g,and the excessive rate of mercury in seed was 6%.The ratio of mercury content in rice root,leaf,stem,shell and seed grain was about 13.5:5.2:1.7:1.2:1.The average enrichment coefficient of rice to mercury in soil was 0.031,and the enrichment ability was weak.The results of correlation analysis showed that there was no significant correlation between soil mercury content and rice mercury content,soil organic carbon (SOC) and pH value,but there was a significant negative correlation between rice mercury content and SOC.