Distribution characteristics of terrestrial PGEs and its trend into the sea around Hainan Island, China

Hainan Island, the largest tropical island in China, is a notable source of pollutants, with a significant proportion of terrigenous contaminants discharged into the ocean. Platinum group elements (PGEs) pose potential risks to both the environment and human health, but research on this topic remains limited. In this study, we analyzed water from Hainan Island offshore area to investigate distribution characteristics of PGEs and its trend into the sea. It is found that the concentration of dissolved PGEs (PGEs_D) is Pd_D > Rh_D > Pt_D, and the concentration of suspended particular PGEs (PGEs_P) is Pd_P > Pt_P > Rh_P. Concentrations of PGEs are generally lower in the western part of the island compared to the east, due to differences in climate, regional development, and coastal zone types, and the high concentration of PGEs is relatively concentrated in the estuary-offshore of large rivers. Affected by the physical and chemical properties of the water, hydrodynamic conditions and the shape of the estuary, the average concentration of PGEs_D increased greatly at first and then decreased slowly from the estuary to the offshore as the average concentration of PGEs_P showed a slow decreasing trend. According to the K_d, Pd and Rh mainly exist in dissolved state, while Pt mainly exists in suspended state. It is calculated that Hainan Island annually discharges an average of Pd 787.98 kg, Rh 33.14 kg, and Pt 193.48 kg into the sea. This study further expands and deepens the research on the environmental geochemical process of new pollutant PGEs.