乐安河中下游重金属时空分布特征及风险评价

Spatio-Temporal Distribution and Risk Assessment of Heavy Metals in Middle and Lower Reaches of Le’an River

为了解乐安河中下游受矿区影响河段的重金属污染水平及其污染程度,于2016年选择不同水文时期,对相应河段表层水体和表层沉积物中6种重金属(Cu、Zn、Pb、Cr、Cd和As)的含量水平、赋存形态及空间分布进行了研究,并采用地累积指数评价法和潜在生态风险指数法对表层沉积物中重金属的污染程度和生态风险进行了评价.结果表明,乐安河中下游水体中Cu、Zn和Cd等重金属浓度在枯水期高于平水期和丰水期.丰、平水期流速与Cd、Pb、Cu和Cr等重金属浓度表现出显著的正相关关系.表层沉积物中Cu、Zn、Pb和Cd的污染水平较高,重金属含量沿程分布特征存在季节差异,枯水期沉积物中重金属含量在河流靠近矿区处最高,而在丰、平水期则分别在下游和河口处达到最高值.沉积物中重金属除Cd以可交换态为主外,其余重金属形态组成中残渣态比重较高.地累积指数法评价结果显示乐安河受到Cu偏重度污染和Cd中度污染.单因子潜在生态风险指数法显示,Cd的潜在生态风险指数较高,部分河段存在严重风险.

The Le’an River is a main tributary of the Poyang Lake,which is the largest freshwater lake in China.The aim of this study is to research the distribution and potential ecological risks of heavy metals in the middle and lower reaches of the Le’an River,which is contaminated by nearby copper mines.Sediment and water samples were collected from 12 stations during the dry,wet,and normal season in 2016,respectively.The geo-accumulation index and potential ecological risk index were used to determine general pollution characteristics of trace metals in sediments.Results suggested that sediments in the Le’an River were considerably polluted by Cd,Pb,Cu,and Zn.Sediment concentrations of heavy metals showed significant spatial variations.The concentrations of heavy metals such as Cu,Zn,and Cd in water are higher in the dry season than in the normal and wet seasons.The distribution of heavy metals along the river is influenced by hydraulic conditions.The flow velocities in wet and normal seasons are positively correlated with the concentrations of heavy metals such as Cd,Pb,Cu,and Cr.There are seasonal differences in the distribution characteristics of heavy metals in surface sediments.In the dry season,the concentration of heavy metals in sediments is the highest in the middle reaches of rivers near mining areas,while during the wet and normal season,it reaches the highest value in the lower reach near the estuary.Except for Cd,whose major form of heavy metal in the sediment is in an exchanging state,the other heavy metals occur mainly in stable states.The assessment of the geo-accumulation index showed significant Cu,Cd,and Cr pollution.Among the heavy metals investigated,Cd was likely to result in more harmful effects.