The researchers studied the levels of heavy metals in sediment from four bays in Hainan Island, South China. They found that the main sources of heavy metals were from land-based pollution and natural geological factors. Sediment with finer grains tended to have higher levels of heavy metals. Overall, the pollution levels in the sediment were low, with arsenic being the most concerning metal. The study showed that the heavy metals in the sediment pose a low ecological risk.