Spatial and seasonal characteristics of dissolved heavy metals in the aquaculture areas of Beibu Gulf, South China

To study the contamination of heavy metals in the aquaculture area of Beibu Gulf, the concentrations of seven metals in seawater were investigated. The results showed that significant seasonal and spatial distributions of heavy metals were observed in the four aquaculture areas. Generally, the heavy-metal concentrations in the Maowei Sea were higher than the other three aquaculture areas, which may be related to local industrialization and urbanization development. The concentrations of some metals were obviously higher in wet seasons than in dry seasons, which may be attributed to the seasonal river discharge, rainfall and seawater intrusion. Compared to other regions, some metal levels revealed relatively high contamination. Remarkably, the concentrations of Hg, Cu and Cd were much higher than concentrations found in the past 20 years in the seawater of the Guangxi Beibu Gulf, suggesting that there were increasing anthropogenic inputs of those metals in the aquaculture areas. The assessment of ecological risk index (ERI) indicated that the highest ERI value was found in the Maowei Sea, followed by Pearl Bay, Lianzhou Bay and Hongsha. Hg is the main ecological risk factor, and the heavy-metal contamination in the aquaculture areas must not be ignored.