Potential Toxic Elements (Ptes) in the Surface Sediments of Beibu Gulf, South China Sea: Spatiotemporal Variation, Geochemical Fractionation and Ecological Risk Assessment

Abstract

Surface sediment samples from three different depth groups were collected in the Beibu Gulf during spring and summer to determine the fractions, potential toxicity, and associated risks of eight potential toxic elements (As, Cd, Cr, Cu, Hg, Ni, Pb, and Zn). Temporally, the results demonstrated that the average concentration of As was higher in spring than the one in summer, while the concentrations of other elements were higher in summer, especially for Zn. Spatially, the T1 group (Depth: < 35 m) exhibited the highest average concentrations of Cd, Cu, and Pb in spring, with Cu being the lowest. In contrast, the concentrations of As, Cu, Ni, and Zn were highest in the T1 group during summer. In terms of fractions, there was an increase in the proportions of reducible state and oxidizable state for Cr, Ni, Pb, Hg, and Zn. The Risk Assessment Code (RAC) showed a decrease in risk levels for As, Cu, Cd, and Zn during summer. However, Cd presented a heightened risk level, with its RAC being the lowest in the T1 group during summer. The secondary phase and primary phase (RSP) assessment showed that As, Cd, and Zn were consistent with the RAC assessment results. Additionally, the RSP for Ni was the lowest in the T1 group in spring. These findings indicated that the spatiotemporal toxicity of potential toxic elements in the sediments of Beibu Gulf varied based on morphological differences, offering novel insights for addressing potential toxic element pollution in the Beibu Gulf.

Keywords: Potential toxic element fractions, sediment, Beibu Gulf, RAC, RSP, Ecological and health risk