茅尾海沉积物重金属空间分布特征与生态风险

Spatial Pattern and Ecological Risk of Heavy Metals in Sediments from Maowei Sea,Southern China

于2010年1月在茅尾海采集了7个沉积物样品,分析了不同深度沉积物的基本理化性质及w(As)、w(Cd)、w(Cu)、w(Fe)、w(Hg)、w(Mn)、w(Ni)、w(Pb)和w(Zn),并采用潜在生态危害指数法进行了潜在生态风险分析.结果表明:这些元素的质量分数空间分布差异显著,总体上呈湾内大于湾外,其中w(Cd)和w(Hg)平均值分别为1.1、0.3 mg/kg,污染最为严重并有加重的趋势;Cd污染可能与周边农田磷肥使用及磷矿开采有关,而Hg污染可能主要是大量使用化石燃料所致.重金属(除As外)质量分数与w(OM)、w(Fe)和w(TN)密切相关,其中w(Cd)与w(TP)密切相关,说明生物和化学过程都显著影响这些元素的空间分布.w(Cu)、w(Hg)、w(Ni)、w(Pb)和w(Zn)之间呈极显著正相关(P<0.01),说明这几种重金属可能具有同源性;而沉积物中w(Cd)与w(Zn)、w(Pb)、w(Ni)和w(Cu)均呈显著负相关(P<0.05),暗示Cd的来源及生物地球化学过程与其他元素不同.该海域重金属潜在生态危害指数依次为Cd>Hg>Pb>Zn>Cu>As,其中Cd与Hg属于中等生态危害;靠近茅岭江汇入区的采样点重金属潜在生态危害指数较高,属于中等生态危害,其余采样点的综合污染也已接近中等生态危害水平.

In Guangxi Province, the Maowei Sea plays an important role in the local aquaculture and oyster nursery through supporting the high productivity. However, the heavy metal pollution in the estuary has deteriorated over the past decades. There are few studies on the spatial pattern and potential ecological risk of heavy metals in the sediments from this estuary. In the present study, sediment samples （0-30 cm） were collected in seven sites of Maowei Sea in January, 2010. The physio-chemical characteristics （e.g., pH, particle size） as well as the concentrations of heavy metals （i.e., As, Cd, Cu, Fe, Hg, Mn, Ni, Pb, and Zn）, organic matter, total nitrogen （TN） and total phosphorus （TP） were determined in the laboratory. Meanwhile, the potential ecological risk of heavy metals was estimated by using the Hakanson index. The results showed the significant differences in the spatial distribution of heavy metals and the higher concentrations of heavy metals in the inner estuary than the outer part. The pollution of Cd （1.1mgkg in average） and Hg （0.3mgkg in average） were the most serious among these heavy metals. Moreover, there was an increasing trend for Cd and Hg pollution over years. The pollution of Cd and Hg might be associated with the intensive use of phosphate fertilizers, the mining of phosphate ore and the combustion of fossil fuels nearby the estuary. The concentrations of heavy metals except for As, were significantly correlated with the concentrations of organic matter, Fe and total nitrogen, while Cd was highly correlated with TP. It suggested that both biological and chemical processes had significant effects on the geochemical cycling of these heavy metals. On the other hand, significantly positive relationships were observed among Cu, Hg, Ni, Pb and Zn（P〈0.01）, suggesting that they were homologous. Interestingly, significantly negative relationships between Cd and Zn, Pb, Ni, Cu were documented （P〈0.05）, indicating that pollution sources and biogeochemistry of Cd were differed from the other metals. Finally, the potential ecological risks of metals in sediments of Maowei Sea decreased as the order：Cd〉Hg〉Pb〉Zn〉Cu〉As, and the potential ecological risks caused by Cd and Hg had reached up to the middle level. Moreover, the integrated ecological risks for the sites nearby the outlet of the Maoling River were relatively high, reaching up to the middle level, while those for other sites approached the middle level as well. Therefore, reducing pollution of Cd and Hg would have priority in local environmental management and improvement program.