Improved Calculations of Heavy Metal Toxicity Coefficients for Evaluating Potential Ecological Risk in Sediments Based on Seven Major Chinese Water Systems

Abstract

Several methods have been used to assess heavy metal contamination in sediments. However, an assessment that considers both composite heavy metal speciation and concentration is necessary to accurately study ecological risks. This study improved the potential ecological risk index method and calculated the toxicity coefficients of seven heavy metals: Arsenic (As), Cadmium (Cd), Chromium (Cr), Copper (Cu), Nickel (Ni), Lead (Pb), and Zinc (Zn). The newly calculated toxicity coefficients were validated by using previously published heavy metal distribution data of the Henan section of the Yellow River. The calculation procedure is based on the principle that the abundance of heavy metals in the environment and their bioavailable forms affect the toxicity of heavy metals. The toxicity coefficients for the seven heavy metals were calculated as follows: As = 10, Cd = 20, Cr = 5, Cu = 2, Ni = 5, Pb = 5, Zn = 1. Ecological risk assessment of the Henan section of the Yellow River using the improved toxicity coefficients revealed that the ecological risk of Cd and total heavy metals is higher than previous calculations, reaching the strength and moderate risk levels, respectively. The improved potential ecological risk index method is more sensitive to heavy metal pollution and thus provides a better indication of ecological risk. This is a necessary improvement to provide more accurate pollution assessments.

Keywords: heavy metal pollution; potential ecological risk assessment; release effect; toxicity coefficient.

Figure 1

Potential ecological risk assessment of the Henan section of the Yellow River. (A) Potential ecological risk index reported in the literature. (B) Potential ecological risk index calculated using improved toxicity coefficients. RI and RII refer to the potential ecological risk index of composite heavy metals before and after improvement, respectively. $E_r^i$ and ${EI}_r^i$ refer to potential ecological risk factors for individual heavy metals before and after improvement, respectively. The red color indicates the potential ecological risk for each metal, and the blue color indicates the potential ecological risk index for composite heavy metals.