Heavy metals in coastal wetland sediments of the Pearl River Estuary, China

Sediment quality in coastal wetlands of the Pearl River Estuary was concerned since the wetlands were used for land reclamation, aquaculture and wildlife protection, and meanwhile served as one of the main ultimate sinks for large amount of heavy metals discharged from the rapidly developing Pearl River Delta. Total concentrations of heavy metal, such as Zn, Ni, Cr, Cu, Pb, and Cd, and their chemical speciation were investigated. Results showed that the sediments were significantly contaminated by Cd, Zn and Ni with concentration ranges of 2.79–4.65, 239.4–345.7 and 24.8–122.1 mg/kg, respectively. A major portion (34.6–46.8%) of Pb, Cd, and Zn was strongly associated with exchangeable fractions, while Cu, Ni and Cr were predominantly associated with organic fractions, residual, and Fe–Mn oxide. Cd and Zn would be the main potential risk and the sediment quality is no longer meeting the demand of the current wetland utilization strategies.