Risk Assessment of Heavy Metal Pollution by Three Plants at Zihu River in Nanjing, China

The concentrations of heavy metals (As, Cr, Cd, Cu, Zn, Mn, Ni and Pb) were measured in the water, sediment, and three common plants (Rorippa indica, Rumex acetosa and Orychophragmus violaceus) from Nanjing Forestry University reach of Zihu River, China. Results showed that the toxic threshold values exceeded the upper limits for Cd and Mn in water. In the same way, toxic threshold values exceeded the limitation for As, Cd, Cu, Ni, Pb and Zn in sediment. Overproof Cd, Cu, Mn, Ni, Pb and Zn were also found in rhizosphere soil. Average concentration of Zn was higher in sediment, followed by Mn in both water and rhizosphere soil. It was found that heavy metals (Cd, Cu, Ni, Pb, As and Zn) in water may be mainly derived from metal processing, electroplating industries, industrial wastewater, and domestic sewage. Positive correlation was observed between As and Cu, As and Ni, Cr and Pb, Cu and Ni, Pb and Zn in water. Moreover, significant positive correlations between Ni and As were observed. Preliminary judgment showed that sediment has a depuration effect on As, Cu, Ni, Cr, Pb and Zn in water, according to correlation coefficients of water and sediment. Comparing the relations between sediment and rhizosphere soil, Cr, Cu, Ni, Pb and Zn in the rhizosphere soil were mainly from the sediment, and Mn was mainly from water. Three plants played active roles on enrichment of As, Cr, Cu, Mn, Ni, Pb and Zn, particularly, Zn and Mn can be accumulated to higher concentration in these three plants. As content in rhizosphere soil was found to be lower than sediment, indicating As was most absorbed by the plants. Thus, three plants were playing a potential role in environment inductors.