渤海西北近岸海域表层沉积物重金属污染及评价

ASSESSMENT OF HEAVY METAL POLLUTION OF THE SURFACIAL SEDIMENT IN NORTHWESTERN BOHAI SEA

对取自渤海西北近岸海域的189个表层沉积物进行了重金属元素、粒度和有机碳(TOC)分析,查明了研究区重金属的分布特征和潜在污染水平。结果表明,As、Cr、Pb、Zn的空间分布比较均衡,Cd、Cu、Hg的空间变异系数较大,低值区都集中在昌黎沿海海域,高值区基本都集中在沿岸河口位置,总体上呈现出由西北部沿岸海区向东南降低的趋势。Cu、Cr、Pb、Hg与黏土含量、TOC之间表现出较强相关性。Pearson相关分析表明,黏土是重金属元素的主要载体,TOC是控制重金属元素的次要因素。根据地质累积指数法(Igeo)评价得出,渤海西北近岸海域仅在个别区域受到轻微污染,大部分区域沉积物底质环境良好。重金属富集因子(EF)显示研究区沉积物污染程度明显高于Igeo计算结果,多数重金属元素均处于中度污染水平,这可能与计算EF值时所取的区域背景值存在偏差有关。两种重金属元素评价方法同时表明Hg元素在沿岸河口位置存在一定程度污染,这与陆上人类经济活动向河口排放的污染物质经河流排入海有直接关系,说明人类经济活动给沿岸水域造成了一定程度的污染。

189 surfacial samples collected from the offshore area of north-eastern Bohai sea are analyzed for heavy metal elements,grain size and organic carbon（TOC）in this paper.The distribution pattern of the heavy metals and potential pollution levels are studied.Results show that the spatial distribution of As,Cr,Pb,Zn is more or less balanced,whereas the Cd,Cu,Hg are rather high.Low values of the spatial variation coefficients appear in the coastal waters of Changli,and high values occur in the coastal estuaries.In general,the coefficient decreases from northwest to southeast.Cu,Cr,Pb and Hg show a strong correlation with clay and TOC content of the sediment.Pearson correlation analysis suggests that clay is the main carrier of heavy metal elements,and the TOC is the second factor which plays significant roles in heavy metal pollution.Geological accumulation index（Igeo）evaluation shows that the nearshore areas of northwest Bohai sea are not polluted by heavy metals except a few places where slight pollution may occur.The heavy metal enrichment factor（EF）,however,tells us another picture that the pollution of sediments in the study area is on a moderate level,significantly higher than that Igeo says,probably owing to the higher regional background used for calculation of the EF values.All the two methods used for evaluation of heavy metal element pollution confirm that Hg element pollution does exist in the coast estuaries to certain extent,and it is directly related to human activities.The pollutants are discharged into the rivers by human being,and then carried by rivers to the sea.