Risk Assessment And Source Apportionment Of Heavy Metals In Typical Rivers Of Taihu Basin

Taihu basin is one of the most developed regions of China. With the rapid growth of economy and population, large amounts of wastewater containing heavy metals are discharged into waters of the basin, causing serious pollution. As a multi-district region, prevention and cure of heavy metals in the basin is rather difficult. The knowing of concentrations, ecological risks and possible sources of heavy metals in rivers, especially transboundary rivers of Taihu basin is the basis and precondition of the heavy metal control in the basin.To provide evidence for the prevention and treatment of the heavy metal pollution in Taihu basin, this study measured the concentrations of V, Cr, Mn, Co, Ni, Cu, Cd, Sb, Ba, T1 and Pb in water and surface sediment samples collected from May 2015 to January 2016 (summer, autumn and winter) in Taipu River, a typical drinking water source reserve and Kunshan reach of Wusong River,a typical industrial water area which are both located in the interprovincial areas in Taihubasin. And the concentrations of total nitrogen (TN), ammonia nitrogen (NH3-N), nitrate nitrogen (NO3-N), total phosphorus (TP), orthophosphorus (PO4-P), chemical oxygen demand (CODMn) and total suspended substances (SS) in water samples were also measured. Then, the pollution conditions of the studied heavy metals in water were assessed by Water Quality Index (WQI) and NemerowComprehensive Index, and the pollution conditions and ecological risks of the studied heavy metals in surface sediments were assessed by Geo-accumulation Index, Pollution Load Index and Potential Ecological Risk Index. And then, the multivariate techniques such as correlation analysis (CA), principle components analysis (PCA) and hierarchical cluster analysis (HACA) were applied to the source apportionment of heavy metals. The main results of this study were:(1) Though the total concentration levels in water samples were low, the maximum concentrations of Mn, Ni, Sb, Tlwere all higher than the limits of surface water as drinking water resource (GB3838-2002). Generally, for water samples, the seasonal heavy metal concentrations were decreased as winter> autumn> summer, whereas the concentrations in the Taipu River were lower than those in Kunshan reach of the Wusong River and there were almost no differences of the spatial distribution for the two rivers.Generally, for surface sediments, theheavy metalconcentrations of the two rivers were both higher than the background values for soils of Taihu basin or Jiangsu Province, with Sb and Cu beyond the values most among the studied metals. Most of the studied heavy metals in sediments have no obvious spatial and seasonal differences and the metal concentrations in the two rivers were both well-distributed.(2) The results of Nemerow single factorpollution index assessment showed that the most polluted element was Mn, followed by Sb and Ni in the water of Taipu River and Kunshan reach of Wusong River. The assessment results of WQI and NemerowComprehensive Index showed that there were generally no pollution risk of heavy metals in the water of Taipu River, however, the pollution level of heavy metals in the water of Kunshan reach of Wusong River was mild by WQI and medium by Nemerow comprehensive index.The results of Geo-accumulation Index and Pollution Load Index showed that the most polluted metal was Sb, followed by Cu in surface sediments of Taipu River and Kunshan reach of Wusong River, and the results of Pollution Load Index also showed that the two rivers both had medium pollution risks of heavy metals. The assessment results of Potential Ecological Risk Index showed the the main hazardous metal was Sb, followed by T1 assessed by Potential Ecological Risk Index, and there were strong potential ecological risks of heavy metals in both rivers.(3) Correlation analysis and principle components analysis of heavy metal concentrations in water and surface sediments as well as the contents of TN, NH3-N, NO3-N, TP, PO4-P, CODMn and SS in water were applied to identify the possible sources of heavy metals, basing on the existing data of point sources along both rivers. Hierarchical cluster analysis of heavy metals were also applied to further verify the hypothesis of heavy metal sources. Results showed that:The import of tributaries was an important source of heavy metals in Taipu River, whereas, the contribution of industrial activities was relatively low. The main sources of heavy metals in water of Taipu River were:V, Co may come from endogenesis release of sediments; Ni, Cd and Pb may come from the import of tributaries; Cr, Mn, Cu and Sb may come from endogenesis release, tributary import and industrial activities; Ba may come from endogenesis release and industrial activities; Tl may come from endogenesis release and tributary import. The main sources of heavy metals in surface sediments of Taipu River were:V, Cr, Ni and Sb may come from the import of tributaries; Cu, Cd and Tl may come from tributary import and industrial activities; Ba and Pb may come from ributary import, industrial activities and natural sources; Mn and Co may come from both natural sources and anthropogenic activities.In Kunshan reach of Wusong River, the industrial activities had significant impacts on heavy metals. In water, V, Mn, Co, Ba and Tl may come from endogenesis release of sediments; Cd and Ni may come from industrial activities; Cr, Cu, Sb and Pb may come from both endogenesis release and industrial activities. In surface sediments, V, Cr, Co, Ni, Ba, Tl, Pb may come from both natural sources and industrial activities; Mn and Cd may come from natural sources; Cu and Sb may come from industrial activities.