东江下游水环境重金属污染特征及现状评价

测定东江下游包括东江干流、东江支流和东莞运河的8个监测断面的水质及表层沉积物中As、Ni、Pb、Cd、Cu、Zn、Cr和Hg的质量比,并应用地积累指数法和潜在生态风险评价法对东江下游水环境的重金属污染潜在风险进行评价。结果表明,东江下游表层沉积物中重金属积累明显,Cd的地积累指数对应的污染程度为极强;Hg为中—强;Cu、Zn在东江干流为中,在东江支流和东莞运河达到强—极强。潜在生态风险评价显示,东江下游区段(包括东江干流、东江支流和东莞运河)的潜在生态危害指数接近或超过300,表明重金属引起的东江下游潜在生态风险程度达到了重度;存在潜在生态风险的重金属类物质主要是Cd、Hg和Cu,其危害程度由大至小依次为:Cd>Hg>Cu。水质监测结果显示,东江下游枯水期水质堪忧,Hg已超出地表水Ⅲ级水质标准。

Assessment of heavy metal pollution downstream of Dongjiang River

The water quality and concentrations of heavy metals including As, Ni, Pb, Cd, Cu, Zn, Cr, and Hg in surface sediments at eight monitoring sections of the Dongjiang River＇s main stream, its tributaries, and the Dongguan Canal downstream were examined. The index of geo-accumulation and potential ecological risk evaluation methods were used to evaluate the potential ecological risk of heavy metal pollution downstream of the Dongjiang River. The results show that heavy metals had accumulated in the surface sediments downstream of the Dongjiang River. The enrichment extent of Cd, according to the index of geo-accumulation, was very intense, the enrichment extent of Hg was moderate, and that of Cu and Zn was moderate in the main stream but intense in the tributaries and the Dongguan Canal. The potential ecological risk assessment shows that the ecological risk index was close to or greater than 300 downstream of the Dongjiang River, including the main stream, tributaries, and the canal, indicating that the total potential ecological risk caused by heavy metals was severe. Cd, Hg, and Cu were the main heavy metals contributing to the potential ecological risk, and their hazard ratings were in the following descending order： Cd, Hg, and Cu. The results from water quality monitoring show that the water quality downstream of the Dongjiang River was worrying during the dry period, when the concentration of Hg exceeded the Class Ⅲ standard of the Environmental Quality Standards for Surface Water.