Beyond the tube well: probabilistic assessment of combined drinking-water, cooking-water and rice-borne arsenic exposure in rural Bangladesh and its implications for mitigation design

Groundwater arsenic in Bangladesh has historically been managed as a drinking-water problem, yet inorganic arsenic (iAs) also reaches households through rice and through the water used to cook it. This study develops a probabilistic, multi-pathway exposure model for rural Bangladeshi adults that couples drinking water, cooking water retained in rice and rice-grain iAs, and uses it to compare five mitigation scenarios: no intervention (S0), switching drinking water only (S1), switching both drinking and cooking water to a low-arsenic source (S2), point-of-use iron-based filtration (S3), and S2 combined with improved rice cooking (S4). The shallow-well arsenic distribution was anchored on national survey exceedance fractions, and 105 Monte Carlo iterations with common random numbers propagated variability in intake, body weight, rice contamination, cooking practice and exposure duration. Risks were characterised with both the legacy and the 2025 US EPA toxicity values and with the JECFA benchmark dose. Under S0, the mean average daily dose was 5.15 µg/kg/day (median 1.60; 90% interval 0.46–21.6), 34.5% of adults exceeded the BMDL0.5 of 3.0 µg/kg/day, and drinking water contributed 69% of the mean dose. Drinking water dominated exposure only above a crossover concentration of 16.5 µg/L. Switching drinking water alone reduced the mean dose by 65%, but left cooking water responsible for 40% of the residual dose; switching both uses reduced it by 79%, and adding improved cooking by 85%. Filtration matched source substitution on the median but not in the upper tail. Even under S4, rice kept the median hazard quotient above unity (2.33 with the legacy reference dose). Arsenic mitigation in Bangladesh should therefore be designed as an integrated water–food intervention in which cooking water is explicitly included and rice-borne iAs is treated as the next priority.