Hydrochemical characteristics, quality and health risk assessment of nitrate enriched coastal groundwater in northern China

Groundwater quality is an essential factor restricting regional sustainable development owing to water resource scarcity, especially in coastal regions. Coastal groundwater is affected by natural conditions and strong human activities, and the evolution of water quality is extremely complex. Information on the hydrochemistry evolution and nitrate contamination status of coastal groundwater under the conjunctive effects of natural processes and human activities is a vital requirement for groundwater resource management in coastal regions. Thus, this study integrated traditional hydrochemical analysis approaches, the entropy-weight water quality index (EWQI), and the health risk assessment model to analyze hydrochemical characteristics, quality, and nitrate health risks in a typical coastal region (i.e., southern Laizhou Bay) simultaneously affected by seawater intrusion and anthropogenic activities, as well as to explore the dominant mechanisms controlling groundwater quality. The results indicated that the concentrations of major hydrochemical constituents in groundwater exhibited wide variability. The NO3- concentration varied from 0.59 to 824.80 mg/L; it surpassed the WHO drinking water standard (50 mg/L) at 89.47% of sampling sites. The predominant hydrochemical types of groundwater were SO4 center dot Cl-Ca center dot Mg and HCO3-Ca center dot Mg. Governing factors influencing groundwater chemistry were recognized as rock weathering, inverse cation exchange and anthropogenic activities, and nitrate contents were largely controlled by agricultural practices. The computed EWQI showed that 55.26% of groundwater samples possessed EWQI values greater than 57, which is relatively poor-quality groundwater. The poor-quality groundwater was concentrated in the southwestern part of the study area. Non-cancer risks of nitrate in 96.71%, 94.74%, 89.47%, and 89.47% of the groundwater samples were unacceptable for infants, children, teens, and adults, and the spatial distribution of the hazard quotient (HQ) was in accordance with the spatial pattern of nitrate concentration. These findings can guide the exploitation and utilization of groundwater resources and water quality conservation in coastal regions.