Inconsistency and comprehensiveness of risk assessments for heavy metals in urban surface sediments |
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Authors: | Yu G B Liu Y Yu S Wu S C Leung A O W Luo X S Xu B Li H B Wong M H |
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Institution: | a Key Laboratory of Urban Environment and Health, Institute of Urban Environment, Chinese Academy of Sciences, Xiamen 361021, China b Graduate University of Chinese Academy of Sciences, Beijing 100049, China c Croucher Institute for Environmental Sciences, and Department of Biology, Hong Kong Baptist University, Kowloon, Hong Kong, China |
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Abstract: | Numerous indices have been developed to assess environmental risk of heavy metals in surface sediments, including the total content based geoaccumulation index (Igeo), exchangeable fraction based risk assessment code (RAC), and biological toxicity test based sediment quality guidelines (SQGs). In this study, the three indices were applied to freshwater surface sediments from 10 sections along an urbanization gradient of the Grand Canal, China to assess the environmental risks of heavy metals (Cu, Pb, Zn, Cd, and Cr) and to understand discrepancies of risk assessment indices and urbanization effects regarding heavy metal contamination. Results showed that Cd, Zn, and Pb were the most enriched metals in urban sections assessed by Igeo and over 95% of the samples exceeded the Zn and Pb thresholds of the effect range low (ERL) of SQGs. According to RAC, Cu, Zn, Cd, and Cr had high risks of adversely affecting the water quality of the Grand Canal due to their remarkable portions of exchangeable fraction in surface sediment. However, Pb showed a relative low risk, and was largely bounded to Fe/Mn oxides in the urban surface sediments. Obviously, the three assessment indices were not consistent with each other in terms of predicting environmental risks attributed to heavy metals in the freshwater surface sediments of this study. It is recommended that risk assessment by SQGs should be revised according to availability and site specificity. However, the combination of the three indices gave us a comprehensive understanding of heavy metal risks in the urban surface sediments of the Grand Canal. |
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Keywords: | Heavy metals Geoaccumulation index (Igeo) Risk assessment code (RAC) Sediment quality guidelines (SQGs) Urban surface sediment The Grand Canal of China |
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