Predicting the Permissible Limit of Arsenic in Irrigation Water for Rice Cultivation

This study establishes, for the first time, a permissible arsenic limit for irrigation water to ensure the safe cultivation of rice, a dietary staple in South Asia. Arsenic contamination of irrigation water is a major health risk for approximately 110 million people in this region. An incubation study was conducted using 420 monolithic soil columns from 10 arsenic-contaminated sites under two irrigation regimes (rainfed and irrigated). Using a logistic regression model, a threshold concentration for arsenic in irrigation water was identified as 190 μg L–1. A nonparametric bootstrap simulation (n = 100,000) was performed, yielding a 95% confidence interval of 163.78–190.20 μg L–1, which confirmed the model’s stability. The threshold was validated with field samples and effectively classified rice grain arsenic concentrations. These findings provide a reference for managing irrigation practices to safeguard food safety in arsenic-endemic rice-growing regions of South Asia.