太湖主要入湖河口表层沉积物重金属分布特征及风险评价

摘要

To reveal the distributive characteristics and ecological risk of heavy metals in the estuarine sediment of the inflow rivers in Taihu Lake, surface sediments were collected from the estuaries of 12 inflow rivers located in the western and northern shores of Taihu Lake. Concentrations of five heavy metals (Cu, Zn, Ni, Pb, Cd) were quantified for the sampled sediments, and the spatial distribution characteristics were analyzed. The pollution extent and potential ecological risk of each heavy metal were evaluated based on the geo-accumulation index (Igeo) and the potential ecological risk factor (riE) respectively. The results indicated that all of the 12 main inflow rivers had been confronted with heavy metal contamination to certain extents in the surface estuarine sediments. The average concentrations of Cu, Zn, Ni, Pb, Cd were 63.04, 173.11, 56.71, 37.05, 2.23 mg∙kg-1 respectively. Spatial heterogeneity was found in the distribution of different heavy metals: the estuaries of inflow rivers Daganghe (DGH), Wuxigang (WXG), Miaodugang (MDG), Dapugang (DPG), Chendonggang (CDG), Guandugang (GDG), Hongxianggang (HXG) and Shedugang (SDG) were mainly polluted by Cd, while the estuaries of Shatanggang (STG), Taigeyunhe (TG), Zhihugang (ZHG) and Liangxihe (LXH) were polluted by a combination of Cu, Zn, Ni and Pb. According to geo-accumulation index (Igeo), the pollution extent of heavy metals in surface sediment followed the order as: Cd>Cu>Zn>Ni>Pb. According to ecological risk factor (riE), the potential ecological risk of heavy metals in surface sediment followed the order as: Cd>Cu >Ni>Pb>Zn, and Cd was the major pollutant for risk. Among the 12 inflow rivers’ estuaries, MDG and SDG were of serious ecological risk, DGH, WXG, DPG, GDG and HXG were of severe ecological risk, CDG and TG were of moderate ecological risk, STG, ZHG, LXH were of low ecological risk. It was demonstrated that the levels of potential ecological risk of heavy metals in the estuaries of inflow rivers located between DGH and SDG were higher than that between STG and LXH, yet attentions should also be paid to the accumulation of Cu, Zn, Ni and Pb in the estuarine sediments between STG and LXH.%为揭示太湖主要入湖河口表层沉积物重金属分布特征及其生态风险，采集太湖西岸和北岸12条主要入湖河口表层沉积物样品，对沉积物中5种重金属元素（Cu、Zn、Ni、Pb、Cd）的含量及空间分布特征进行了分析，并利用地累积指数法和潜在生态风险指数法分别研究了表层沉积物重金属的累积程度及生态风险。结果表明，调查的12条入湖河流河口表层沉积物均受到不同程度的重金属污染，Cu、Zn、Ni、Pb、Cd的平均质量分数分别为63.04、173.11、56.71、37.05、2.23 mg∙kg-1。各重金属在空间分布上具有差异性，总体表现为大港河（DGH）、乌溪港（WXG）庙渎港（MDG）、大浦港（DPG）、陈东港（CDG）、官渎港（GDG）、洪巷港（HXG）、社渎港（SDG）河口表层沉积物以重金属Cd污染为主，而沙塘港（STG）、太滆运河（TG）、直湖港（ZHG）、梁溪河（LXH）河口表层沉积物表现为 Cu、Zn、Ni、Pb的复合污染。地累积指数法评价表明，各入湖河流河口表层沉积物重金属的污染程度表现为Cd>Cu>Zn>Ni>Pb。潜在风险指数（ riE ）表明各重金属的潜在生态风险表现为 Cd>Cu>Ni>Pb>Zn，主要污染物为 Cd。其中庙渎港（MDG）和社渎港（SDG）处于严重风险状态，大港河（DGH）、乌溪港（WXG）、大浦港（DPG）、官渎港（GDG）、洪巷港（HXG）处于重度风险状态，陈东港（CDG）、太滆运河（TG）处于中度风险状态，其余点位生态风险较低。研究表明，西岸入湖河流表层沉积物重金属潜在生态风险等级高于北岸，但北岸入湖河流河口表层沉积物中Cu、Zn、Ni、Pb的累积也应当得到重视。