Changes in heavy metal content and their potential ecological risk in the surface sediments of Lingding Bay from 2010 to 2020

The Pearl River estuary (PRE) is one of the estuaries with the most serious heavy metal pollution in China. To understand the changes of heavy metal pollution in this area in the last 10 years, sampling at surface sediments was carried out in 2010 and 2020 at nearly the same locations and quantities in the Lingding Bay area, where pollutants were most likely to accumulate. In addition, the contents of heavy metals (V, Cr, Co, Ni, Cu, Zn, Cd, and Pb) in all the samples were measured by using ICP-MS. Results show that the average contents of Cd, Cr, Cu, Zn, and Pb in the sediment samples collected in 2020 significantly decreased than those of 2010, except for V and Ni whose contents changed slightly, and Co increased significantly. The evaluation results of the enrichment factor method and potential ecological risk index method reflected that the enrichment degree and potential ecological risk of Cd, Cu, Pb, Zn, and Cr in surface sediment of 2020 have been alleviated to varying degrees compared to that 10 years ago. Cd was in moderate to significant enrichment in over half of the samples. V and Ni were not or slightly enriched in both time periods, but the proportion of slight enrichment in 2020 increased compared to 2010. The enrichment degree and potential ecological risk of Co increased compared to 2010, but it was still at a low level. From a spatial perspective, the four major waterways in Lingding Bay, especially the Hongqili and Jiaomen Waterways, were still the places with the most severe heavy metal pollution in PRE. Among the 8 heavy metals in concentration, Cd concentration was the highest, the greatest human impact and the strongest potential ecological risk, followed by Cu and Pb.