Selected metals (Cr, Ni, Cu, Pb, Zn, Cd and As) in surface sediments from the Pearl River Estuary (PRE) and Daya Bay (DYB) were analyzed to observe their total concentrations and chemical phase portioning. It was shown that the amounts of all contents, except Pb, have decreased over the past decade. The mean concentrations in PRE, excluding Pb, were significantly higher than those in DYB. Based on the PLI and mERM-Q, it was revealed that the highest potential ecological risk zones were in the northwest of PRE and sub-basins of DYB. An overwhelming majority of sediments had a 21% probability of toxicity in PRE and 9% probability of toxicity in DYB. The speciation analyzed by the optimized BCR sequential extraction method showed that, in both areas, Cr, As and Ni were present dominantly in the residual fraction and thus of low bioavailability, while Cd and Pb were found to be abundant in the non-residual fraction and thus of high potential availability, indicating significant anthropogenic sources. The partitioning of Cu and Zn showed a significant difference between the two areas. The source analysis shows that the pollutants resulted primarily from anthropogenic material, and secondly from the input of natural weathering products in PRE, while being mainly attributed to natural geological sources of metals, followed by industrial wastewater and aquaculture activity in DYB.
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