Spatial distribution and human health risk assessment of nitrate and fluoride in drinking water of Maragheh County, Iran (2018-2023) using Monte Carlo simulation.

Monitoring nitrate and fluoride levels in drinking water is essential due to their potential adverse health effects. While studies have assessed these contaminants across Iran, comprehensive analyses of their spatial-temporal distribution and probabilistic health risks remain scarce for Maragheh County. This study addresses this gap by applying Monte Carlo simulation (MCS) and principal component analysis (PCA) to 132 drinking water samples collected from 2018 to 2023. This novel framework identifies contamination sources and quantifies risks across demographic groups. Results revealed that 97% of nitrate and 96% of fluoride concentrations met World Health Organization (WHO) guideline limits. PCA explained 76.5% of total variance, with EC, TH, TDS, and Ca2+ as dominant factors. The water quality index (WQI) rated over 88% of samples as excellent and less than 1.5% as poor. Fluoride posed negligible health risks (HQ < 1), but nitrate exposure yielded elevated hazard indices (HI > 1) for children, signaling potential non-carcinogenic effects. Overall, findings underscore the need for ongoing monitoring, better wastewater and fertilizer management, and targeted protections for vulnerable groups in agricultural regions.