Severe Nitrate Pollution and Health Risks of Coastal Aquifer Simultaneously Influenced by Saltwater Intrusion and Intensive Anthropogenic Activities.

Groundwater quality is critical for regional sustainability and human well-beings in coastal regions, because groundwater is an important water resource for these areas facing water scarcity. Anthropogenic activities might induce nitrate pollution, whereas saltwater intrusion could decrease coastal groundwater discharge into sea to subsequently cause the persistent accumulation of pollutants in coastal aquifer. Rare information is available on the nitrate pollution of coastal aquifer under simultaneous influences of saltwater intrusion and intensive anthropogenic activities. This study investigated the distribution, pollution, possible sources, and potential health risks of groundwater nitrate of typical coastal aquifer simultaneously influenced by saltwater intrusion and intensive anthropogenic activities. The average/maximal concentration of groundwater nitrate was 173.70/824.80 mg/L, indicating the severe accumulation of nitrate in the coastal aquifer. Concentrations of nitrate in coastal groundwater were much higher than those in adjacent seawater. Groundwater salinization did not have significant effects on nitrate distribution. Groundwater in 87.6% of sampling sites was not suitable for drinking based on nitrate evaluation criterion. Anthropogenic activities might induce nitrate pollution in approximately 94.7% of sampling sites. Sources, including sewage and manure, soil nitrogen, and ammonium fertilizers, contributed to groundwater nitrate with concentration > 100 mg/L in the study area, whereas sewage and manure were the predominant source affecting groundwater nitrate in 97.5% of sampling sites. Groundwater nitrate exerted unacceptable noncancer health risks for infants, children, teenagers, and adults in more than 87.6% of the study area. Infants and children were the most susceptibly influenced by groundwater nitrate. It is urgent to take effective measures for controlling groundwater nitrate pollution in the study area.