Distribution, sources and influencing factors of heavy metals in the Ledong Sea, South China Sea.

The Ledong Sea Area is located on the southwest side of Hainan Island. In recent years, with the development of industrialization and urbanization, the problem of heavy metals in marine sediments has gradually become a global problem, and research on this topic is of great significance for nearshore environmental protection and coastal management. This paper analysed the heavy metal content of 97 surface sediments in the Ledong Sea, indicating unpolluted to moderately polluted and low to moderate risk. Cu, Zn, Hg, Pb, Cr, and Cd are highly correlated, with similar origins, and originate from rivers carrying industrial wastewater, domestic sewage, and weathered material from the parent rocks, which are subsequently redistributed under the action of ocean dynamics. The distribution of Hg is mainly influenced by feed and biological metabolites during the farming process. As originates from rivers carrying large amounts of agricultural pesticide and fertilizer residues.

Sedimentary records of environmental evolution in Dongzhai Port mangrove swamps (South China) over the last hundred years: Insights from corrections of grain-size effects.

Mangrove sediments play a vital role in the biogeochemical processes of elements by behaving as both sources and/or sink for nutrients and trace metals. Under the combined impacts of grain-size effects and human activities, it is difficult to accurately assess the sources and degree of pollutants. For this purpose, two cores were collected from a mangrove swamps of Dongzhai Port (South China) and analyzed for temporal distributions of grain size, nutrients, major and trace elements, and 210Pb activities. Due to the significant vertical variation of grain size with depth, linear regression analysis was conducted based on trace metals (i.e., Pb, Cr, Ni, Cu, Cd, Zn) and normalized element Al to reconstruct local environmental background. The results showed that the contents of Cu, Cd, and Zn in the surface layers exhibited significantly increasing trends since the 1980s, with maximum contents of 9.06, 0.16, and 228.66 µg g-1, and their enrichment factors up to 1.52, 1.40, and 1.50, respectively. It should be attributed to shrimp farming and domestic sewage, indicating slight anthropogenic inputs. The evolution process was divided into three stages in Dongzhai Port over the last 100 years: before 1980 AD, 1980-2000 AD, and from 2000 AD to the present, corresponding to the stages of natural deposition, domestic pollution, and aquaculture pollution, respectively.