Source Apportionment and Health Risk Assessment of Nitrate, Fluoride, and Manganese in Groundwater Surrounding Livestock Farms in Central China

Groundwater supporting agro-pastoral regions is vulnerable to contamination from livestock effluents; this study evaluates shallow aquifers near farms in Henan Province to clarify sources and health risks of nitrate, fluoride, and manganese. We combined hydrochemical analysis with principal component analysis (PCA) and absolute principal component score-multiple linear regression (APCS-MLR) for source apportionment and applied Monte Carlo simulation (10,000 iterations) to quantify noncarcinogenic risk for children and adults via ingestion and dermal contact. Groundwater chemistry reflects carbonate weathering with contributions from evaporite dissolution and cation exchange. Source apportionment attributes ~73% of NO₃ ^- to anthropogenic inputs, ~90% of F^- to evaporitic/fluoride-bearing minerals, and ~76% of Mn²⁺ to redox-driven mobilization. Median hazard quotients (HQs) for all indicators were below 1. The median total hazard index (HI) was 1.18 for children and 0.80 for adults. At the 95th percentile, ingestion-driven nitrate HQs were 5.69 in children and 2.50 in adults, and fluoride HQs were 2.50 in children and 1.53 in adults; dermal exposure was negligible. Manganese HQs were 0.78 in children and 0.47 in adults, indicating low concern. Overall, nitrate risk reflects anthropogenic inputs from fertilizers and sanitation, whereas fluoride is largely geogenic. Management should prioritize reducing nitrate sources and, in parallel, implement feasible fluoride mitigation and removal.