Date Published: March 14, 2019
Publisher: Public Library of Science
Author(s): Xia Li, Wanqing Chi, Hua Tian, Yongqiang Zhang, Zichen Zhu, Daniel Rittschof.
Considering the serious land-based pollution and the weak water exchange ability of western Laizhou Bay, it is essential to conduct an ecological risk assessment of the pollutants in this area. In this study, the ecological risk caused by heavy metals deposited in the surface sediments and those resuspended in the seawater of western Laizhou Bay was evaluated using probabilistic approaches. First, the concentrations of seven heavy metals, namely As, Cd, Cr, Cu, Hg, Pb, and Zn, in the surface sediments and seawater of western Laizhou Bay were detected during the spring and autumn of 2016. The concentrations of As, Cd, Cr, Cu, and Pb were found to be at levels comparable to those in the other global coastal systems, while those of Hg and Zn were lower than those in other coastal areas. Next, an ecological risk assessment of heavy metals in the surface sediments was performed using a typical potential ecological risk index and refined by using a Monte Carlo simulation. The results suggested low risk for the heavy metals detected in the sediments of western Laizhou Bay, with the exception of Hg in September 2016, which showed a probability (0.03%) of moderate risk. Meanwhile, the aquatic ecological risk assessment of the heavy metals was performed by applying a combination of hazard quotient (HQ) and joint probability curve. While the ecological risk of Cd, Hg, and Pb was found to be acceptable, the HQs for Cr, Cu, and Zn were greater than 1, and the overall risk probability of their adverse effects was higher than 0.05, suggesting certain ecological risk. Specifically, in the case of As, the overall risk probability was lower than 0.05, suggesting that its ecological risk was acceptable, although its HQ was greater than 1. Thus, by applying the probabilistic approaches, the ecological risk of the heavy metals in western Laizhou Bay was better characterized in this study, avoiding both overestimation and underestimation of ecological risk.
Due to their poor biodegradability, easy bioaccumulation, and high toxicity, heavy metals discharged into the sea from different sources may pose serious threats to marine organisms. For example, the spore release of Ulva pertusa is inhibited by exposure to Cu, Cd, Pb, and Zn ; Cd arrests the molting of the estuarine crab Chasmagnathus granulata by preventing the normal peaking of the ecdysteroids needed for molting ; disorganization of epithelial cells is observed in the gills of Arctic charr (Salvelinus alpinus) after exposure to Hg (15 μg/L) for 12 h ; DNA damage is induced in marine bivalve mollusk (Mytilus edulis) by Cu exposure at a low concentration of 18 μg/L ; and the embryo development of Ruditapes decussatus is observed to be inhibited when the median effective concentration (EC50) values are 4.2 μg/L for Hg and 9.1 μg/L for Cu .
The presence of the heavy metals namely As, Cd, Cr, Cu, Hg, Pb, and Zn was detected in the surface sediments and seawater of western Laizhou Bay during the spring and autumn of 2016; and their concentrations were found to be comparable to or lower than those in other coastal areas around the world. The typical potential ecological risk index and Monte Carlo simulation suggested low risk for the sediments of western Laizhou Bay, with the exception of Hg during September 2016, which showed the probability of a moderate risk. The HQ and JPC indicated certain ecological risk for Cr, Cu, and Zn, and acceptable risk for Cd, Hg, Pb, and As in the surface seawater. The ecological risk of heavy metals in western Laizhou Bay was better characterized in this study by applying the probabilistic approaches.