Characterizing pollution degrees, sources, and health risks of heavy metal(loid)s in groundwater from a Se-enriched area against a regional Se-deficient background.

Rational exploitation of Se-enriched groundwater resources is frequently constrained by co-occurring pollution by heavy metal(loid)s (HMs), due to the homologous provenance of Se and other HMs. It is therefore critical to systematically characterize HMs pollution levels, identify contamination sources, and assess corresponding human health risks. A total of 119 shallow groundwater samples were collected and investigated using multiple hydrochemical and statistical approaches. Results showed that Fe, Mn, Al, Ba, Se, and As concentrations in certain samples exceeded their corresponding Grade Ⅲ thresholds stipulated by the Chinese national groundwater quality standard, with Al and Fe as the main pollutants. Selenium in the groundwater exhibited moderate enrichment and closely co-varied with multiple HMs originating mainly from coal-related industrial activities. Quantitative source apportionment using the APCS-MLR model, combined with multiple lines of spatial evidence, revealed that the potential sources of groundwater HMs, in descending order of contribution, were heavy industrial activities (33.2%), a mixed source of coal combustion and mineral weathering (24.7%), hydrogeochemical processes (17.9%), traffic emissions (16.2%), and agricultural inputs (7.94%). Deterministic health risk assessment indicated low non-carcinogenic risks but elevated carcinogenic risks, particularly for adults. In contrast, the probabilistic assessment based on Monte Carlo simulation revealed that the exceedance probabilities for non-carcinogenic risk were 82.7% for adults and 92.5% for children, while those for carcinogenic risk were 99.8% for adults and 12.0% for children, respectively. Sensitivity analysis identified As concentration as the dominant driver of both non-carcinogenic and carcinogenic risks. Spatially, groundwater samples with elevated health risks were predominantly distributed in the central hilly areas where coal mines and heavy industries are concentrated. The findings support the safe utilization of Se-enriched groundwater and HM pollution control in similar Se-deficient regions with localized enrichment.