Fluorine distribution, health risk, and geological and anthropogenic controlling factors in central Guizhou Province, Southwest China

Abstract

Fluorine (F)-enriched soils, resulting from geogenic processes or superimposed by anthropogenic activities, have raised significant concerns due to their phytotoxicity and potential threats to human health. Soils in central Guizhou Province exhibit F enrichment, with a mean F concentration of 1067 mg/kg. However, the associated human health risks and geochemical mechanisms driving F enrichment in these soils remain insufficiently understood. In areas with a natural geological background, the average concentrations of F in rice, vegetables, drinking water, and ambient air are 1.54 mg/kg, 0.54 mg/kg, 0.16 mg/L, and 0.29 μg/m³, respectively. In contrast, samples collected near phosphorous chemical plants demonstrate elevated F concentrations: 1.78 mg/kg in rice, 1.53 mg/kg in vegetables, 0.20 mg/L in drinking water, and 11.98 μg/m³ in ambient air. Fluorine in soils was immobilized by apatite and clay minerals, and hardly transferred into water and crops. The fixation of F^- by Ca²⁺ in water and by Fe/Al hydroxides and clay minerals in bottom sediment further reduces F concentrations in water. As a result, hazard quotient (HQ) values below 1.0 indicate negligible fluorine-related health risk in geological background regions. However, ambient air near phosphorous chemical plant exhibited a 41.3-fold increase in F concentration compared to geological background regions. Fluorine-laden emissions can be directly inhaled or deposited on vegetable leaves and orally ingested into human bodies. Improvement of F-rich waste gas disposal and restricted leafy vegetable cultivation are effective measures to reduce F health risks in phosphorous chemical plant regions.