巢湖市城区黑臭水体综合水质与底泥重金属污染研究

Studies on comprehensive water quality and heavy metal pollution in sediment of black and odorous waters in urban area of Chaohu

文章以巢湖市城区6个典型黑臭水体为研究对象,设定27个采样点,测定了表层水体中溶解氧(dissolved oxygen,DO)、CODCr、BOD5、NH3-N、总磷(total phosphorus,TP)的质量浓度及底泥中Cu、Ni、Zn、Pb、Cd、Hg、As等7种重金属元素的质量比。选用综合水质标识指数法、地累积指数法、潜在生态风险指数法及污染负荷指数法对黑臭水体综合水质与底泥重金属污染特征进行分析,并根据参评重金属元素的种类和数量对生态风险评价分级标准进行调整。结果表明:6个水体的综合水质指数大于7.0,水质级别为劣Ⅴ类且黑臭;底泥中的主要金属污染物是Cd、Hg、Cu,其中4个水体的Cd污染程度为偏中度,6个水体的Hg、Cu污染程度为轻度;底泥中重金属生态风险主要来源于Cd、Hg,其中5个水体的Cd生态风险级别为较强或很强,6个水体的Hg生态风险级别为中等或较强;底泥中7种重金属元素的综合污染程度为中等,综合生态风险级别为中等—较强。因此,对于黑臭水体的治理不可仅局限于消除黑臭与富营养化,底泥中重金属污染不可忽视。

Six typical black and odorous waters in urban area of Chaohu were selected as the research objects,setting up 27 sample sites.The value of dissolved oxygen(DO),CODCr,BOD5,NH3-N and total phosphorus(TP)in the surface water and the content of seven heavy metals in sediment including Cu,Ni,Zn,Pb,Cd,Hg and As were determined.The comprehensive water quality identification index method,the cumulative index method,the potential ecological risk index method and the pollution load index method were used to analyze the comprehensive water quality and the characteristics of heavy metal pollution in sediment of black and odorous waters respectively.According to the types and quantity of heavy metals,the grading standards of ecological risk assessment were adjusted.The results showed that the comprehensive water quality indices of the six water bodies were more than 7.0.The waters were black and odorous and the quality level of them were worse than GradeⅤ.The main metal pollutions in sediment were Cd,Hg and Cu.Among them,Cd in four water bodies was moderately polluted,while Hg and Cu in six water bodies were slightly polluted.The ecological risk of heavy metals in sediment mainly came from Cd and Hg.Five water bodies had strong or very strong Cd ecological risk,and six water bodies had moderate or strong Hg ecological risk.The comprehensive pollution degree of seven heavy metals in sediment was moderate,and the comprehensive ecological risk was concentrated in moderate-slightly strong.Therefore,the treatment of black and odorous water should not be limited to the elimination of black-odor and eutrophication.Heavy metal pollution in sediment cannot be ignored.