Human health risk assessment of nitrate in repeatedly boiled water using Univariate regression and Monte Carlo simulation

Exposure to nitrate-contaminated water can increase the risk of methemoglobinemia and cancers. This experimental study investigate the effects of repeated boiling on nitrate level and their associated health risks. In this experimental study, 30 water samples were collected-15 tap water samples and 15 prepared using standard synthetic solutions containing standardized nitrate concentrations (prepared by dissolving potassium nitrate)-with nitrate levels measured using a DR 5000™ UV-Vis spectrophotometer. This study used Univariate regression to analyze boiling cycles, volume reduction, and nitrate levels. Health risks were assessed via EPA's HQ method with Monte Carlo simulations for probabilistic analysis. Findings showed tap water's initial nitrate concentration (0.56 ± 0.08 mg/L) increased significantly after boiling (p < 0.001). Regression analysis revealed a 0.75 mg/L nitrate rise per boiling cycle (R² = 0.64, p < 0.001), with remaining water volume inversely correlated (R² = 0.68, p < 0.0001). Health risk assessment indicated EPA safety thresholds (HQ > 1) were exceeded for all age groups, particularly infants (HQ = 2.850) and adults (HQ = 6.982). Monte Carlo simulations confirmed elevated Hazard Indices (mean HI > 4.19), far exceeding EPA's safe limit (HI = 1). Sensitivity analysis found adults most vulnerable, likely from lifetime nitrate exposure. The study shows that repeated water boiling significantly concentrates nitrates, posing serious health risks. Public awareness about this issue is crucial. Further investigations should assess long-term health outcomes in high-risk populations and examine socio-cultural determinants of boiling practices to guide targeted health interventions.