Variations in the distribution of trace elements in coral sand sediments at the green turtle nesting ground in the Xisha Islands, South China Sea.

Coral sand sediments were collected from green turtle nests, vegetation lines, and the high tide line in the Xisha Islands, South China Sea. The contents of trace elements (TEs)-chromium (Cr), copper (Cu), zinc (Zn), selenium (Se), cadmium (Cd), lead (Pb), arsenic (As), and mercury (Hg)-along with reference elements, titanium (Ti), aluminum (Al), ferrum (Fe), scandium (Sc) were analyzed to assess ecological risks and identify potential sources. Results revealed significant spatial variations in TE concentrations: Cu, Zn, Se, and Pb levels were significantly higher in nest sediments than at the vegetation and high tide lines (p < 0.0001), whereas As concentrations were significantly lower in nests compared to the other two sites (p < 0.0001). Pollution assessment based on contamination factor (CF) and enrichment factor (EF) values indicated generally low pollution levels for Cr, Cu, Zn, and Pb, with localized exceptions for Cu and Zn. Hg showed moderate pollution in most samples, while Cd exhibited moderate to extreme pollution. Source analysis suggested that Zn and Hg along the vegetation line may be influenced by atmospheric deposition and plant litter. In high water line sediments, Cu, Cd, and Hg were likely incorporated into coral skeletons during growth. In contrast, Cu, Zn, Se, and Pb in nest sands might be impacted by the deposition of eggshells and unhatched eggs.