Spatial distribution and ecological risk assessment of heavy metals in sediment around the coastal oyster reefs in Guangdong, China

The distribution and sources of heavy metals in sediments near natural oyster habitats along the Guangdong coast were investigated from July 2022 to February 2023. Sediments were predominantly sandy (>55 % sand). Heavy metal concentrations followed the order: Zn > Pb > Cu > Cr > As > Cd > Hg. One-way ANOVA revealed significant spatial differences in six metals except Cu, with higher concentrations near estuarine, bay, urban, and harbor areas. Overall, 4.1 % of samples exceeded China's Class I standard for Cu, Pb, Zn, and Cd. Only stations G24 (Zhuhai) and G41 (Zhanjiang) had poor sediment quality; 94 % of stations were suitable for shellfish aquaculture. The geo-accumulation index indicated about 30 % of samples were slightly polluted, mainly by As and Pb. Over 90 % of samples exhibited low ecological risk; however, Hg, Cd, and Pb posed moderate to high risk at 5.5 %, 4.9 %, and 2.1 % of stations, respectively. Compared with historical data, most metal levels remained low, though Cu in western Guangdong and Pb in the Pearl River Estuary reached historically high levels. Key sources were riverine input, urban discharge, port activities and industries.