Pollution Level and Potential Ecological Risk of Heavy Metals in Surface Sediment of A Severe Polluted River in Nanjing

Abstract

Black and smelly water bodies are generally caused by the enrichment and release of large amount of pollutants such as organic matter and heavy metals in sediments. Surface sediments at 11 sections of a severe polluted urban river in Nanjing were monitored to assess the pollution level and potential ecological risk. Results show that surface sediments were seriously polluted by heavy metals and contents of heavy metals were all higher than respective background values. Cd and Hg were major pollutants with relative high contents, following by Ni, As, and Zn. Comprehensive pollution load index of the river reached 4.1, indicating a "Progressive deteriorate" pollution level, with a contribution degree order of Cd>Hg>Pb>Zn>Cu>Ni>Cr>As. Most sections of the river exhibited high potential ecological risk with a contribution order of Cd>Hg>Pb>Cu>Ni>As>Zn>Cr. Additionally, there are significant positive correlations between Cu and organic matter (r = 0.947, p<0.01), and between Cu and nitrogen and phosphorus (r = 0.866 and 0.860, p<0.01). Cd and Hg contributed most to the high ecological risk of sediment and possibly came from similar anthropogenic sources due to significant correlations. Ecological dredging and disposal methods for the sediments should be seriously considered when comprehensively rehabilitating such a river.