Source Apportionment and Health Risk of Heavy Metals and Inorganic Nitrogen in Groundwater of a Coastal Plain, China

Groundwater in coastal aquifers is highly vulnerable to contamination driven by intensive anthropogenic activities and hydrogeochemical processes such as seawater intrusion. This study investigated the occurrence, source apportionment, and health risks of heavy metals (Cd, Pb, and Ni) and inorganic nitrogen species (NO₃ ^--N, NO₂ ^--N, and NH₃-N) in groundwater from the Qinhuangdao coastal plain, North China. A total of 46 groundwater samples were collected and analyzed. Positive matrix factorization (PMF) and absolute principal component scores-multiple linear regression (APCS-MLR) were jointly applied to identify pollution sources, and a probabilistic human health risk assessment incorporating Monte Carlo simulation was conducted to quantify uncertainty. Results indicated that the mean concentrations of Cd, Pb, and Ni complied with Chinese groundwater quality standards, whereas NO₃^--N and NH₃-N exceeded the Class V threshold at several sites, suggesting localized nitrogen contamination. PMF resolved three primary sources: industrial discharge (dominated by NO₂ ^--N), domestic sewage (NH₃-N), and agricultural activities (NO₃^--N and heavy metals). Health risk assessment showed that Cd posed a potential carcinogenic risk through ingestion and dermal exposure, whereas the noncarcinogenic risks of Pb and Ni remained within acceptable limits. Monte Carlo simulation confirmed the robustness of the deterministic estimates and identified the Cd carcinogenic slope factor and ingestion rate as the most sensitive parameters. Source-oriented risk apportionment further indicated that agricultural activities contributed the largest share of carcinogenic risk. These findings highlight the importance of controlling agricultural nonpoint pollution and provide a scientific basis for groundwater protection and risk management in coastal plain aquifers.