天津渤海湾4种重金属的分布及生态风险评价

Distribution and Ecological Risk of Four Heavy Metals in the Tianjin Coastal Area of Bohai Bay,China

为了探究渤海湾近岸海域水体中重金属污染状况及其潜在生态风险,以天津渤海湾近岸海域为研究区域,共设置34个采样点,于2013年9月17-23日采集水样,分析表层水体中铜(Cu)、镉(Cd)、铅(Pb)和锌(Zn)4种常见重金属的空间分布特征及其潜在生态风险。结果表明,Cu、Cd、Pb和Zn的浓度分别为2.47~8.27μg/L、0.06~0.26μg/L、2.21~8.26μg/L和5.26~70.32μg/L,平均值分别为4.56μg/L、0.12μg/L、4.72μg/L和36.65μg/L。根据我国《海水水质标准》(GB3097-1997),4种重金属基本满足Ⅰ类或Ⅱ类海水水质标准;基于4种重金属的物种敏感性分布(species sensitivity distribution,SSD)曲线,分别获得相应的5%物种危害浓度(HC5),并采用风险熵(RQ)对4种金属的生态风险进行评价,发现研究区域表层水中存在生态风险的重金属为Cu和Zn,与之相比Cd和Pb的生态风险可以忽略不计。研究认为我国目前的《海水水质标准》低估了Cu和Zn对水生生物的影响,不能够满足对水生生物的保护需求,应引起足够的重视。

Heavy metal pollution in Bohai Bay and the presence of heavy metals in source water have aroused con- siderable public concern. This study investigated the spatial distribution of four heavy metals （Cu, Cd, Pb and Zn） in the Tianjin coastal area of Bohai Bay, China, and their potential ecological risk was evaluated according to the National Seawater Quality Standard of China （GB3097-1997） and the Species Sensitivity Distribution （SSD） method. Water samples were collected at 34 stations, Sep 17 -23, 2013 and the content of the four heavy metals were determined using ICP-MS. During the study period, water parameter ranges were as follows： water temperature, 14.77 - 20.45℃ ; pH, 7.9 - 8.25 ; DO, 5.58 - 9.13 mg/L and salinity, 24.7 - 28.7g/kg. The range of and av- erage concentrations for each heavy metal were ： Cu, 2.47 - 8.27 μg/L, 4.56 μg/L ; Cd, 0.06 - 0.26μg/L, 0. 12 μg/L; Pb 2.21 - 8.26 μg/L, 4.72 μg/L and Zn, 5.26 -70.32 μg/L, 36.65 μg/L. The spatial distribu- tion of the four heavy metals differed ： The highest Cu concentrations occurred in Haihe Estuary and the coastal rec- reational area; high Cd and Zn concentrations were observed in the coastal recreational area and high Pb concentra- tions were observed at off-shore sites. Based on their average concentration and the Chinese National Seawater Quality Standard （GB3097-1997） , Cu and Cd meet the first grade standard, while Pb and Zn meet the second grade standard. The HC5 （hazardous concentration for 5% of the sensitivity species） value for each metal was ob- tained from their corresponding SSD curve and are as follows： Cu, 1.90 μg/L; Cd, 5.31 μg/L; Pb, 36.9 μg/L and Zn, 12.36 μg/L. The concentration of Cu exceeded the HC5 value at all 34 sites and the concentration of Zn exceeded the HC~ value at 30 sites. The range of risk quotient （RQ） values for Cu was 4.87 - 13.13 and for Zn, 1.28 - 17.06, indicating that Cu and Zn pose a high ecological risk （ RQ 〉 1 ） throughout the study area. In con- trast, the concentrations of Pb and Cd at all sites were lower than their HC5 values, with RQ values of 0.03 -0.15 for Cd and 0.18 -0.67 for Pb. The Cd risk was low （RQ 〈0.1） at 30 sites and medium （0.1 〈 RQ 〈 1 ） at the remaining 4 sites. For Pb, the RQ values indicate a medium ecological risk at all sites. The adverse effects of Cu and Zn on aquatic life are underestimated by the Chinese National Seawater Quality Standard （ GB3097-1997 ） com- pared to the risk assessment using SSD. We suggest that Cu and Zn pollution in the study area should be given more attention.