东平湖表层沉积物中砷赋存特征及风险评价

Arsenic speciation characteristics and risk assessment of surface sediment in Dongping Lake

为了解东平湖表层沉积物中砷的形态赋存特征及其生态环境风险,采用Tessier修正连续提取法对东平湖表层沉积物样品中砷的总量及形态赋存特征进行了分析,并运用风险评估指数法和沉积物重金属质量基准法对其环境风险进行了初步评价.结果表明,东平湖表层沉积物中总砷含量范围为8.59—22.76 mg·kg-1,均值为(15.69±2.64)mg·kg-1,是山东省土壤背景值的1.68倍,黄河干流沉积物背景值的2.09倍;沉积物各形态砷平均含量表现为:残渣态(11.90 mg·kg-1)>腐殖酸结合态(1.84 mg·kg-1)>铁锰氧化态(1.13 mg·kg-1)>碳酸盐结合态(0.34 mg·kg-1)>强有机质结合态(0.32 mg·kg-1)>离子交换态(0.12 mg·kg-1)>水溶态(0.04 mg·kg-1),沉积物中的砷主要以残渣态存在,其中生物可利用态砷占总砷的平均比例为24.2%.东平湖表层沉积物砷总体表现为低生态风险;73.3%的采样点砷含量处于可能效应水平(PEL)和临界效应水平(TEL)之间,26.7%的采样点高于可能效应水平(PEL).

In order to understand the chemical speciation and the ecological environmental risk of arsenic(As)in the sediment of Dongping Lake,the chemical forms of As in surface sediment samples collected around Dongping Lake was analyzed by using the Tessier seven-step sequential extraction procedure.The environmental risk of As was evaluated by the methods of risk assessment code(RAC)and sediment quality guidelines(SQGs).The results showed that total As concentrations in the surface sediment ranged from 8.59 to 22.76 mg·kg-1,with an average of(15.69±2.64)mg·kg-1,and the average concentration of As was about 1.68 times of the soil background value of Shandong Province and 2.09 times of the sediment background value from the main stream of the Yellow River.In terms of As speciation,As mainly existed in residual fraction,and the average concentrations of the seven forms followed the sequence of the residual fraction(11.90 mg·kg-1)>the humic acid fraction(1.84 mg·kg-1)>the Fe-Mn oxide fraction(1.13 mg·kg-1)>the carbonate fraction(0.34 mg·kg-1)>the strong organic matter fraction(0.32 mg·kg-1)>the ion-exchange fraction(0.12 mg·kg-1)>the water-soluble fraction(0.04 mg·kg-1).In addition,the average percentage of bioavailable As which was calculated as the sum of the concentrations of the first six fractions except the residual fraction was 24.2%.The assessment results of RAC suggested that As in the sediment of Dongping Lake posed low ecological risk,while according to the results of SQGs,As concentrations in 73.7%sediment samples were in the range of the probable effects level(PEL)and the threshold effect level(TEL)and in 26.7%samples exceeded the PEL.