重庆主城区次级河流表层沉积物重金属污染特征及风险评价

山地城市次级河流因季节性降雨容易导致沉积物中污染物形成"二次污染",沉积物可能具有重金属潜在生态风险.本文采集了重庆市主城区19条次级河流表层沉积物,分析了7种重金属元素(V、Cr、Ni、Cu、Zn、Cd和Pb)的污染水平,解析了重金属污染来源,并从流域层面评价次级河流表层沉积物重金属的潜在生态风险.结果表明,与背景值(中国土壤元素背景值)相比,除V外,其它6种重金属元素超标1.1~6.7倍.富集系数分析和主成分分析显示,沉积物中重金属V、Ni和Pb均未发生富集(富集系数小于1.5),且主要来源于自然源.Cd、Zn、Cu和Cr平均富集系数分别为6.63、2.31、1.90和1.40,均存在不同程度的富集;Cr、Zn和Cu主要来源于工业废水的排放.主城区次级河流表层沉积物重金属潜在生态风险指数RI值范围为77~382,均值为228,总体属于中等生态风险等级.空间分布上,重庆主城区西北部汇入嘉陵江的次级河流表层沉积物重金属表现出较高的生态风险,东南部汇入长江的次级河流表层沉积物表现为相对较低的风险.

Pollution and ecological risk assessment of heavy metals in the surface sediments from the tributaries in the main urban districts, Chongqing City

Due to seasonal rainfall, sediments of the tributaries in mountainous cities are easy to be a secondary polluted "source" and may have a potential risk, especially for heavy metals. The surface sediments from 19 tributaries in the main urban districts of Chongqing City, a typical mountainous city, were collected to analyze the sedimentary heavy metal contents and, underlying source of heavy metals was explored and then environmental risk of those metals was assessed by Hakanson potential ecological risk index. The results showed that all heavy metals except for V were 1.1 to 6.7 times higher than that of the corresponding background values. Enrichment factors for V, Ni and Pb in the surfaces sediments were less than 1.5, indicating that these 3 trace elements were originated from natural sources. while higher enrichment factors of Cd, Zn, Cu and Cr(6.63,2.23,1.90 and 1.40,respectively) were observed. Principal components analysis(PCA) revealed that Cr, Zn and Cu were mainly influenced by anthropogenic activities, especially from the discharge of industrial wastewater. Potential ecological risk indexes (RI) for these 19 selected tributaries ranged from 77 to 382(228 averagely) and most tributaries of Jialingjiang River in the northwestern region exhibited a higher ecological risk compared to those southeastern ones. Our study clearly revealed that all these secondary tributaries were moderately polluted by heavy metals,and the potential risk to both Jialingjiang and Yangtze River, and further to the Three Gorge Reservoir, should be further studied in the future.