Spatiotemporal Analysis and Health Risk Assessment of Nitrate in Kan River Basin, Tehran: Application of IRWQI and Monte Carlo Simulation

Introduction: Monitoring and controlling water resources and using health risk assessment approaches for water pollutants are essential for health promotion programs. This study aims to determine the water quality status and its spatiotemporal variation across the Kan River Basin, explore the interrelationship between surface and groundwater quality indices, and assess the nitrate health risk in drinking water. 
Materials and Methods: The water quality index (WQI) was calculated based on the guideline of the Iran Environmental Protection Organization, and spatiotemporal distribution maps were prepared using ArcGIS in 2020. To determine the correlation between IRWQISC and IRWQIGC indices, Spearman's non-parametric test was applied. Furthermore, Hazard Quotient (HQ), Excess Lifetime Cancer Risk (ELCR), and Monte-Carlo Simulation techniques were used to determine the carcinogenic and non-carcinogenic risks of nitrate in three age groups. 
Results: The water resources were classified into three groups of medium quality, relatively good, and good during the study period. All parameters complied with the Iranian water quality standards. Furthermore, the statistical analysis revealed no significant relationship between the surface and groundwater quality indices. The calculated HQ values for infants, children, and adults were 0.661, 0.620, and 0.236, respectively. The ELCR values for infants, children, and adults were 1.06 × 10-4, 0.99 × 10-4, and 0.38 × 10-4, respectively, which, for the infants' group, was higher than the guideline limit of the United States Environmental Protection Agency (USEPA) (10-4). 
Conclusion: The water resources are suitable for drinking purposes. However, more attention is needed to prevent water contamination in the coming years.