北京市凉水河表层沉积物中砷含量及其赋存形态

选择北京市典型的非常规水源补给城市河流(凉水河)为研究对象,采用王水水浴消解法和BCR三步提取法分析了表层沉积物中砷含量及其形态,并利用富集系数法、风险评估指数法和沉积物重金属质量基准法对表层沉积物中砷进行评价.结果表明,凉水河表层沉积物中总砷含量范围是2.18~22.5 mg·kg~(-1),均值为6.01 mg·kg~(-1),多数样点低于北京市土壤中砷的背景值;沉积物中砷主要以残渣态(B4态)存在,平均含量为3.93 mg·kg~(-1);沉积物中各形态砷所占的平均比例顺序为:残渣态(B4态)可还原态(B2态)可氧化态(B3态)弱酸可溶解态(B1态),其中生物有效态砷占总砷的平均比例为39.61%.富集系数法分析结果显示凉水河表层沉积物中砷基本未出现富集;风险评估指数法分析结果显示凉水河60%的采样点表层沉积物中砷含量呈中度风险,40%的采样点呈低风险;沉积物重金属质量基准法分析结果显示凉水河55%的采样点表层沉积物中砷含量低于阈值效应水平(TEL),40%的采样点处于可能效应水平(PEL)和阈值效应水平(TEL)之间.

Arsenic Content and Speciation in the Surficial Sediments of Liangshui River in Beijing

Arsenic (As) content and speciation in the surface sediments of the typical urban river (Liangshui River) with unconventional water sources in Beijing were investigated by different methods, including BCR three-step sequential extraction procedure, enrichment factor (EF), risk assessment code (RAC) and sediment quality guidelines (SQGs). The results showed that total As contents in the surface sediments ranged from 2.18 mg ·kg^-1 to 22.5 mg ·kg^-1, with an average of 6.01 mg ·kg^-1, and most of them were lower than the soil background value. In terms of speciation, As mainly existed in B4 (with an average content of 3.93 mg ·kg^-1), and the contents of the four forms followed the sequence: B4 > B2 > B3 > B1. In addition, the percentage of biological available As was 39.61%. The EF values due to As showed there was not significant enrichment in most studied sediments. The analysis results of RAC showed that the surface sediments from 60% of the sampling sites posed moderate risk, and 40% of the sampling points showed low risk. The results of SQGs showed that As content in the surface sediments from 55% of the sampling points was below the threshold effect level (TEL), and that in 40% of the sampling points was between TEL and probable effects level (PEL).