Abstract:

Long-term mineral exploitation in the south of the Da Hinggan Mountains has adversely affected the riverine ecological environment. Heavy metal pollution and risk assessment of river surface sediments are therefore crucial to protecting riverine ecosystem health in this area. Here, we studied a lead-zinc deposit in the southern section of the mountain range. Six groups of surface sediment samples were collected in the upper, middle, and lower sections of the river that flows through the mine, and analyzed for contents of 19 metals and major elements. The mainly affected heavy metals were identified by correlation and cluster analysis. Soil environmental quality standards and sediment quality criteria were used to evaluate heavy metal contents. The geo-accumulation index (I_geo) and potential ecological risk index (I_peri) were used to assess the pollution degree and potential ecological risk. We found (1) significant positive correlations between the contents of As, Cd, Cu, Pb, Zn, CaO, and MnO, with Pearson correlation coefficients greater than 0.85. These elements and compounds belonged to the same category in a Ward's systematic cluster analysis, indicating that they likely had similar origins. The contents of these seven elements in sediments were greater than background values. Further, their coefficients of variation were large (>60%), indicating that As, Cd, Cu, Pb, Zn, CaO, and MnO contents were significantly affected by mining activities. (2) The Cu content was below the risk screening value (RSV) and threshold effect level (TEL) at all sediment sampling points. The As, Cd, Pb, and Zn contents in the upper and lower river sections were also below the RSV. However, As, Cd, Pb, and Zn contents in the middle section of the river were higher than the RSV, and As, Pb, and Zn contents were higher than the probable effect level (PEL). (3) The sequence of the I_geo of heavy metals in the surface sediments was Cu<As<Zn<Pb<Cd. The I_geo of Cd was 4.29, indicating strong pollution. The sequence of the ecological risk factor (E_r) was Cu<Zn<As<Pb<Cd. The E_r of Cd was 2633.69, indicating a very high risk. Cd accounted for 81.21%-91.65 % of the I_peri, suggesting that Cd was the main source of pollution and risk to the sediments. (4) The heavy metal pollution level of sediments in the middle section of the river was moderate to serious, and the I_peri was up to 5619.87, indicating a very high risk. The pollution level and ecological risk in the middle section were significantly higher than those in the upper and lower sections, indicating that this river section was most affected by mining activities.

Key words: heavy metal, surface sediments, lead-zinc deposit, south of the Da Hinggan Mountains, pollution assessment, ecological risk assessment

摘要：

大兴安岭南段长期矿产开发对该地区河流生态环境造成了巨大压力,评估河流沉积物中重金属的污染状况及潜在生态风险对该地区河流生态环境保护具有重要意义。以大兴安岭南段某铅锌矿区为研究区,在流经矿区河流的上、中、下段沿流向采集了6组表层沉积物样品,测试了其中19种金属与主量元素的含量,通过相关性和聚类分析确定了受主要影响的重金属元素,利用土壤环境质量标准和沉积物质量基准对重金属的含量特征进行了评估,并进一步采用地质累积指数（I_geo）和潜在生态风险指数（I_peri）对重金属的污染程度和潜在生态风险进行了评价。结果表明,（1）研究矿区河流沉积物中As、Cd、Cu、Pb、Zn、CaO与MnO含量两两之间呈显著正相关,Pearon相关系数均大于0.85,Ward系统聚类分析属于一类,指示这些元素在沉积物中很可能具有相似的来源。7种元素在沉积物中的含量均大于其背景值,且变异系数较大（>60%）,表明其含量受矿山开发活动影响显著。（2）沉积物各采样点的Cu含量均低于土壤污染风险筛选值（RSV）和临界效应浓度（TEL）。河流上、下段沉积物的As、Cd、Pb、Zn含量均低于RSV,中段的含量均高于RSV,其中As、Pb、Zn含量高于可能效应浓度（PEL）。（3）沉积物重金属的I_geo从小到大依次为Cu<As<Zn<Pb<Cd,Cd的I_geo为4.29,属重度污染等级。重金属的潜在生态风险因子（E_r）从小到大依次为Cu<Zn<As<Pb<Cd,Cd的E_r为2633.69,属极高风险等级,占I_peri的81.21%—91.65%,表明Cd是沉积物的主要污染和风险来源。（4）河流中段沉积物重金属元素属偏中度-严重污染等级,其I_peri高达5619.87,属极高风险等级,污染程度和生态风险都明显高于上、下河段,表明河流中段受矿山开发活动的影响最为显著。

关键词: 重金属, 表层沉积物, 铅锌矿区, 大兴安岭南段, 污染评价, 生态风险评价