洞庭湖表层沉积物中重金属变化趋势及风险评估

摘要

为掌握洞庭湖重金属污染的变化趋势及风险,利用2007-2017年洞庭湖表层沉积物中Cr、Cu、Pb、Cd、Hg、As的连续监测数据,通过潜在生态风险指数法进行评价,并通过Daniel趋势检验和M-K(Mann-Kendall)突变检验对重金属的变化趋势进行分析,同时结合历史文献数据对1984—2017年洞庭湖沉积物中重金属的演变特征进行分析.结果表明,2007—2017年洞庭湖沉积物重金属RI(综合潜在生态风险指数)范围为32. 63～917. 23,平均值为196. 24,属于"较高"风险水平,空间分布呈南洞庭湖>东洞庭湖>西洞庭湖,不同重金属单因子潜在生态风险水平呈Cd>Hg>As>Pb>Cu>Cr的特征. Daniel趋势检验和M-K突变检验结果显示,2007—2017年除西洞庭湖的w(Pb)、东洞庭湖和西洞庭湖的w(Hg)外,其他重金属质量分数在各湖区都呈下降趋势;东洞庭湖和南洞庭湖重金属潜在生态风险水平分别在2014—2015年和2016年发生了突变. 1984—2017年洞庭湖沉积物中重金属质量分数演变特征分析表明,1984年和1990—1999年全湖重金属综合潜在生态风险分别为"较高"和"中等"水平,2004—2010年和2011—2015年均为"很高"水平,2016—2017年降至"较高"水平,同时w(Cu)、w(Pb)、w(Cd)、w(As)在2016—2017年下降明显,而w(Cr)、w(Hg)还有上升趋势.研究显示,洞庭湖重金属污染在2014—2017年有明显下降趋势,其主要原因可能是湘江和洞庭湖的全面综合治理,Cr、Pb和Hg在部分湖区还存在持续污染,应作为洞庭湖重金属下一步防治的重点.%The variation trend and ecological risk of heavy metals in Dongting Lake sediments were evaluated by the Daniel and Mann-Kendall (M-K) statistic test and the potential ecological risk index using the continuous monitoring data of Cr,Cu,Pb,Cd,Hg and As in the surface sediments of Dongting Lake during 2007-2017,and combined with historical data during 1984-2017 to analyze the characteristics of long-term evolution of the heavy metals in Dongting Lake sediments over the past 30 years. The results showed that the average potential ecological risk index (RI) of the heavy metals in the sediments of Dongting Lake from 2007 to 2017 was 196. 24 (ranging from 32. 63 to 917. 23),suggesting a high ecological risk. The spatial distribution of the RI values was as follows: South Dongting Lake>East Dongting Lake>West Dongting Lake. The decreasing order of the values of the single ecological risk index of the heavy metals was as follows: Cd>Hg>As>Pb>Cu>Cr. The results of the Daniel trend test showed that,except for w(Pb) of West Dongting Lake and w(Hg) of East and West Dongting Lake,the contents of the heavy metals showed a decreasing trend in every lake regions in 2007-2017. The results of the M-K statistic test showed that,in recent 10 years,the RI values of the heavy metals in the sediments of East Dongting Lake mutated during 2014-2015,and that of the South Dongting Lake mutated in 2016. Analysis of the evolution in the last 30 years showed that the RI of the heavy metals in the whole lake was in high and moderate risk in 1984 and during 1990-1999,respectively, presented a very high risk during 2004-2010 and 2011-2015,and reduced to a relatively high-risk level in 2016-2017. In addition,the values of w(Cu),w(Pb),w(Cd),w(As) decreased significantly during 2016 to 2017,however,the values of w(Hg) and w(Cr) increased. Research showed that the pollution of the heavy metals in Dongting Lake sediments presented decreasing trend in the last two or three years, and the control of heavy metals pollution in Dongting Lake and Xiangjiang River may be the main reason for it. The pollution of Hg,Cr,and Pb still existed in some lake regions,and they should be the focus of the next step in the prevention of heavy metals in Dongting Lake.