Comparative evaluation of regulatory health risk assessment frameworks for fluoride-contaminated environments

The Republic of Korea applies a residential soil fluoride standard of 800 mg/kg, while geogenically elevated fluoride occurs in some regions, creating uncertainty about how soil fluoride concentrations translate into potential health risk under multimedia exposure. Because fluoride exposure can also occur through groundwater and food crops, soil concentration alone may not fully characterize total exposure. This study compared health risk assessment guidance and quantify the parameterizations using explainable analyses to support media-integrated management guidance. Fluoride exposure scenarios, including crop intake, drinking water consumption, and soil/dust ingestion, were compared and evaluated using the U.S. EPA risk assessment guidance for superfund (RAGS) and the Korean soil-contamination risk assessment guidelines (KRAG). Simulated fluoride levels ranged from 200 to 4000 mg/kg in soil, 0.5 to 2.5 mg/L in water, and 5 to 40 mg/kg in crops. Additionally, explainable machine learning was applied to identify parameterization inconsistencies and to support guideline-relevant refinement. Children exhibited higher hazard index (HI) to fluoride under RAGS, reaching 9.116, whereas KRAG yielded lower HI estimates under the specified parameterization and, in some scenarios, produced lower HI values for children than for adults. A modified approach, RAGS-K, applies KRAG parameters within the RAGS calculation structure and yielded higher HI estimates than KRAG under the examined scenarios. The results show that intake from water and crops dominates child risk and drives the discrepancy between adult and child risk, supporting further evaluation of media-integrated risk assessment approaches.