农田土壤中汞的吸附分配行为研究

摘要

汞是环境中毒性最强的重金属之一,由于具有持久性、长距离迁移性和生物累积性被列为全球性污染物.土壤是汞重要的源和汇,在汞的生物地球化学循环中发挥关键作用,其理化性质可以显著影响汞的吸附分配行为.本文基于采自全国各地的131份农业土壤样品考察了汞(Hg2+)在土壤中的吸附分配行为,测定了Hg2+的固液分配系数(Kd),并探讨其与p H、有机质(OM)、粒度组成、溶解性有机质(DOM)和总硫等土壤理化性质的关系.利用逐步多元线性回归的方法分析发现旱地土壤对汞Kd的主要影响因素是DOM和土壤粒度,而水田的主要影响因素是总硫.通过淹水实验,进一步探究了土壤氧化还原对Hg2+分配的影响.研究发现,旱地土壤中,大部分土壤在淹水30 d后Kd呈明显增大趋势,继续淹水至60 d的Kd表现为稳定或下降的趋势;大部分水田土壤在淹水条件下Kd未表现出增大的趋势,且随淹水时间呈稳定或下降的趋势.%Mercury is one of the most toxic heavy metals in the environment. It is regarded as a global pollutant due to persistence, long-range transport and bioaccumulation. Soil plays a key role in the biogeochemical cycle of mercury as the source and sink meanwhile, and soil physical and chemical properties have significant effects on the adsorption of mercury. This study investigated the partition coefficients of Hg2+between soil and water (Kd) for 131 agricultural soils collected from all over the country, and discussed the correlations between Kdvalues and physical and chemical properties of soils, such as pH, organic matter (OM), partical size, dissolved organic matter (DOM) and total sulfur. The results showed that the main factors of dryland soils on Kdvalues were DOM and particle size, while the main factor of paddy soils was total sulfur by multiple stepwise regression. The effects of redox of soils on mercury distribution were further investigated by incubation experiment of flooding. It was found that Kdvalues of most of dryland soils showed an obvious increasing after 30 days, then kept stable or decreased after 60 days, while Kdvalues of most of the paddy soils showed a steady or downward trend with the flooding time.