Contamination, ecological risk and source apportionment of heavy metals in sediments and water of a contaminated river in Taiwan

Houjing River, located in Kaohsiung City, is one of the most seriously contaminated rivers in Taiwan. This study analyzed the concentrations of heavy metals (As, Cd, Cr, Cu, Pb, Ni, Zn and Hg) in sediments and water samples collected from this river. Analysis of contamination factor (C-f(I)) and potential ecological risk factor (E-f(I)) of heavy metals in water showed that there were low grades of contamination and potential ecological risk for all heavy metals, suggesting that heavy metals in water were less likely to pose risks to the ecosystem. However, sentiment samples were found to have severe contamination levels based on ranges found in sediment quality guidelines (SQG). The average Cu concentration was almost twice as high as the upper standard values in all the guidelines. Multi-element indices were used to evaluate the synergistic effects of different metals at the sampling sites. The calculated results of different indices, the modified degree of contamination (mC(d)), Nemerow pollution index (P-N) and potential ecological risk index (RI), were in good accordance. 'Heavy' contamination and 'severe' ecological risk were found at three sites, Demin, Zhuwai and Renwu. Cadmium and copper contributed the highest to the ecological risk there. Results of positive matrix factorization modeling identified four sources of heavy metal pollution in both sediments and water. Heavy metal contamination in the Houjing River is attributed to companies carrying out various industrial processes along the riverbank, including traditional metal plating, plastic manufacture and semi-conductor packaging. Therefore, future pollution control and management plans should emphasize the strict regulation of discharge from these industrial activities.