Abstract
Background
Heavy metal pollution of aquatic systems is a global issue that has received considerable attention. Canonical correlation analysis (CCA), principal component analysis (PCA), and potential ecological risk index (PERI) have been applied to heavy metal data to trace potential factors, identify regional differences, and evaluate ecological risks. Sediment cores of 200 cm in length were taken using a drilling platform at 10 sampling sites along the Xihe River, an urban river located in western Shenyang City, China, divided into 10 layers (20 cm each). The concentrations of the As, Cd, Cr, Cu, Hg, Ni, Pb and Zn were measured for each layer. Eight heavy metals, namely Pb, Zn, Ag, Cd, Cr, Cu, Ni, and Hg, were measured for each layer in this study.
Results
The average concentrations of the As, Cd, Cu, Hg, and Zn were significantly higher than their background values in soils in the region, and mainly gathered at 0–120 cm in depth in the upstream, 0–60 cm in the midstream, and 0–20 cm downstream. This indicated that these heavy metals were derived from the upstream areas where a large quantity of effluents from the wastewater treatment plants enter the river. Ni, Pb, and Cr were close or slightly higher than their background values. The decreasing order of the average concentration of the Cd was upstream > midstream > downstream, so were the Cr, Cu, Ni and Zn. The trend of the average concentration of the As was different to the Cd; being highest midstream, followed by upstream and then downstream. The potential factors of heavy metal pollution were Cd, Cu, Hg, Zn, and As concentrations, especially Cd and Hg, whose ecological risks were much higher than those of Ni, Cr, and Pb. The ecological risk levels of all heavy metals were much higher upstream than midstream and downstream.
Conclusions
Industrial discharge was the dominate source for eight heavy metals in the surveyed area, and rural domestic sewage has a stronger influence on the Hg pollution than industrial pollutants. These findings indicate that effective management strategies should be developed to protect the environmental quality of urban rivers.
Evaluating ecological risks and tracking potential factors influencing heavy metals in sediments in an urban river