乐清湾养殖区表层沉积物重金属含量分布及污染评价

以乐清湾养殖区表层沉积物中Cu等7种重金属为研究对象,在野外实地调查取样及重金属含量测定基础上,以中国海洋沉积物质量(GB18668-2002)一类标准值为评价标准,利用单因子指数评价法、内梅罗综合污染指数评价法和沉积物质量基准(sediment quality guideline,SQG),对单项重金属污染程度、多种重金属综合污染效应及重金属潜在生物毒性风险进行了评价。结果表明,乐清湾养殖区表层沉积物重金属含量分布差别明显,所有采样点表层沉积物均受到Cu污染,局部受到严重Hg污染;大部分养殖区表层沉积物重金属污染达到轻度等级;所有养殖区均可发生由Cu偶尔引起的不利生物毒性效应,个别养殖区可发生由Hg频繁引发的不利生物毒性效应。乐清湾养殖区表层沉积物重金属主要来源于沿岸电镀企业废水排放及农药化肥造成的农业面源污染。开展Cu、Hg污染治理修复是实现乐清湾养殖环境安全的迫切需求。

Distribution and pollution assessment of heavy metals in surface sediments of aquaculture area in Yueqing bay

Abstract: Yueqing bay is one of the key sea farming areas in Zhejiang province. Because of the rapid development of coastal economy, large quantities of industrial and agricultural wastewater and domestic sewage have been discharged into Yueqing bay. The environmental reports by the local government state that water quality of Yueqing bay has degraded since 1980s, which has caused a serious threat to the sustainable development of mariculture and coastal ecology. Sediments are sinks of various pollutants and inversely affect water quality. But there are lacks in understanding on heavy metals and other pollutants in sediments. In order to understand the current situation of environment pollution and carry out heavy metal pollution assessment to providing reference for pollution remediation, we studied the pollution of heavy metals including copper (Cu), cadmium (Cd), chromium (Cr), lead (Pb), zinc (Zn), mercury (Hg) and arsenic (As) in surface sediment of mariculture area in Yueqing bay. Based on field investigation, 10 samples of surface sediment were collected in typical aquaculture area. By using atomic fluorescence spectrometer (AFS-930) and atomic absorption spectrometer (AA240Fs), heavy metal contents of the surface sediment samples were determined. According to standard value of the first class in China Marine Sediment Quality Standard (GB18668-2002), single factor index method, nemerow comprehensive pollution index method and sediment quality guideline method were used to evaluate pollution degree of individual heavy metal, integrated pollution effects of several heavy metals and potential biological toxicity risk of heavy metal. The results showed that contents of Cu, Cr, Pb and Zn in sampling point S1 were the highest, which were 69.0, 74.0, 36.7 and 190.0 mg/kg respectively. The highest content values of Cd, As and Hg were 0.30, 26.6 and 0.82 mg/kg from sampling points S9 and S5 respectively. Variation coefficient of Hg content was 0.77, which was the highest and showed most significant difference of spatial distribution. Pollution indexes of Cd, Cr and Pb of all the sampling points were less than 1, and the mean values were 0.40, 0.64 and 0.50 respectively, indicating that surface sediment of aquaculture area in Yueqing bay was not polluted and contents of Cd, Cr and Pb met the quality requirements of surface sediment. Pollution index of Cu in each sampling point was more than 1, and the average value was 1.32, which showed that surface sediment of aquaculture area in Yueqing bay was widely polluted by Cu. Pollution index of Hg reached 4.08, which demonstrated that surface sediment of some aquaculture areas in Yueqing bay was seriously polluted by Hg. Among 10 sampling points, nemero comprehensive pollution index of heavy metal only in sampling point S8 was less than 1, being in safety level. Nemero comprehensive pollution indexes in S1and other 7 sampling points were all above 1, whose pollution levels reached mild. Nemero comprehensive pollution index in sampling point S9 was more than 3, and the pollution level reached severe. The evaluation results of nemero comprehensive pollution index method showed that most of the surface sediment of aquaculture area in Yueqing Bay was slightly polluted by heavy metals. The harmful biological toxic effects of Cu and As may occasionally occur in all of aquaculture areas in Yueqing bay, and harmful biological toxic effects of Hg may frequently happen in some aquaculture areas. It is urgent to carry out heavy metal pollution remediation of Cu and Hg in surface sediment of aquaculture area in Yueqing bay.