Influence of coastal groundwater salinization on the distribution and risks of heavy metals

Coastal groundwater quality significantly affects the regional sustainable development, due to the water resource shortage in coastal zone. Current studies on coastal groundwater have mainly focused on saline water intrusion and over-extraction. Information on the heavy metal pollution of coastal groundwater with salinization trend is limited. This study investigated heavy metals in groundwater from a typical coastal region with intensive anthropogenic activities and saline water intrusion. The southwestern coastal plains of the study area showed significant groundwater salinization trend. Heavy metals in the coastal groundwater mainly originated from anthropogenic activities and groundwater salinization according to principal component analysis. Relative high concentrations of As, Co, Cr, Cu, Fe, Mn, and Ni occurred in the southwestern coast of the study area with high TDS level, indicating that the concentrations of these heavy metals in shallow aquifer of the study area might be influenced by the groundwater salinization. Average concentrations of heavy metals in groundwater of the study area ranged from 0.03 (Cd) to 686.92 (Fe) μg/L. Fe was the dominant heavy metal in groundwater with the maximal concentration of 2333.76 μg/L and exceeding-standard rate reaching 98.23%. Approximately 13.27% of sampling sites showed moderate or higher heavy metal pollution of groundwater based on heavy metal pollution index. Heavy metals in groundwater exerted low ecological risks. Elements Fe, Ni, and As were the main contributors for ecological risks. Cancer risks of heavy metals for both adults and children were high at all sampling sites. Non-cancer risks for adults and children were unacceptable at 4.42% and 17.70% of sampling sites, respectively. The salinization of the coastal groundwater could also lead to the increase in the ecological and health risks of heavy metals in coastal groundwater. These findings provide initial and important information on heavy metals pollution in coastal aquifer with saline water intrusion.