Geochemical speciation, pollution assessment, and source identification of heavy metals in sediment cores of Cau River basin, Hai Duong province

Abstract

Heavy metal contamination in sediment has caused severe threats to the aquatic ecosystem and public health worldwide. Hence, determining the distinct chemical forms of a given heavy metal in sediment is crucial in evaluating its bio-lability and toxicity. This study demonstrates the geochemical speciation using a sequential extraction procedure to fractionate individual phases (exchangeable, carbonate, Fe-Mn oxide, organic, and residual) of nine heavy metals (Cu, Pb, Cd, Zn, Fe, Co, Ni, Mn, and Cr) in the sediment of a rivers system in Hai Duong, a deltaic province in Vietnam. A quantitative assessment of the environmental risk factors (e.g., contamination factor, risk assessment code) and pseudo-partitioning coefficient between pore water and sediment were analysed to define the pollution levels of heavy metals and their contaminated areas. Furthermore, multivariate analyses facilitate a profound comprehension of the contributions to pollution. Analyses of the extracts from the sequential extraction procedure were determined by inductively coupled plasma-mass spectrometry. The results of sedimentary heavy metal speciation indicate that the critical risks of Cd and Mn on the aquatic ecosystem are due to their higher retrieval from the exchangeable fraction. Additionally, an appreciable percentage of Co, Mn, Pb, Zn, and Ni in the carbonate fraction highlights a strong co-precipitation formation or ion exchange-oriented inclination of these metals towards carbonate minerals. Whilst colloids of Fe-Mn oxides act as efficient scavengers for metals such as Fe, Mn, Zn, and Pb, organic matter forms function primarily in trapping Cu, Pb, Fe, Cr, Co, and Ni. Our findings in the ecological risk evaluations and multivariate analyses designate that Cr, Ni, and Fe are ascribed to natural lithogenic origins. In contrast, anthropogenic inputs induce Cd, Mn, Cu, and Pb high-environmental risks.