典型城市河流表层沉积物中汞污染特征与生态风险

以北京市凉水河为研究对象,研究了典型城市河流表层沉积物中汞污染特征与生态风险.采用王水水浴消解法和BCR三步提取法分析沉积物中汞总量及其赋存形态特征,并利用潜在生态风险指数法和风险评估指数法评价汞的生态风险.结果表明,凉水河表层沉积物中总汞含量范围是0.018~3.48 mg·kg~(-1),平均值是0.974 mg·kg~(-1),多数样点高于北京市土壤背景值;表层沉积物中汞主要以残渣态(B4态)存在,平均含量为0.841 mg·kg~(-1),各形态汞所占比例顺序为:残渣态(B4态)可氧化态(B3态)可还原态(B2态)弱酸可溶解态(B1态),其中生物有效态汞占总汞的比例为23.21%.基于汞总量的潜在生态风险评价可知,凉水河各个河段表层沉积物中汞的潜在生态风险程度都处于很高水平(Ei平均值为565);但基于汞形态的生态风险评价可知,汞的生态风险都处于较低水平(B1所占比例平均值为4.80%).

Pollution characteristics and ecological risk of mercury in the surface sediment of a typical urban river

The pollution characteristics and ecological risk of mercury (Hg) in the surface sediments of Liangshui River System (LRS), Beijing were investigated by using the methods including BCR three-step sequential extraction procedure and potential ecological risk index (RI), risk assessment code (RAC). The results show that total Hg contents in the surface sediments ranged from 0.018 mg·kg^-1 to 3.48 mg·kg^-1, with an average of 0.974 mg·kg^-1, and most of them were higher than the soil background value. In terms of speciation, Hg mainly existed in B4 (average content 0.841 mg·kg^-1), and the contents of the four forms were in the following sequence: B4> B3> B2> B1. In addition, the percentage of biological available Hg was 23.21%. The E_i of Hg in the surface sediments of LRS were in high level (RI=565 on average), however, according to the classification of RAC, the risk of Hg was low in the studied sediments.