Age-dependent lifetime dose modeling of Radium-228 in drinking water: Implications beyond the World Health...

The World Health Organization (WHO) recommends a reference level of 0.1 mSv y^-1 for radionuclides in drinking water, derived using adult water-intake assumptions and adult ingestion dose coefficients. While practical for regulatory screening, this approach may underestimate exposure where intake and radionuclide retention vary with age. In this study, an age-dependent lifetime dose accumulation model was developed for Ra-228 in drinking water. Age-specific drinking-water intake rates were combined with ICRP ingestion dose coefficients and time-resolved retention functions to estimate annual, cumulative, and lifetime-averaged effective doses from birth to 70 years. For a reference concentration of 1 Bq L^-1, the cumulative lifetime dose reached approximately 71.4 mSv, corresponding to a lifetime-averaged annual dose of ∼1.02 mSv y^-1, compared with ∼0.50 mSv y^-1 under the adult-based WHO framework. Annual dose peaked during adolescence at ∼2.7 mSv y^-1, reflecting the superposition of retained dose contributions from intakes occurring in earlier years. When interpreted under the simplifying assumption that Ra-228 is the sole radionuclide contributing to ingestion dose, the WHO reference level of 0.1 mSv y^-1 in adults (≈0.2 Bq L^-1) corresponds to peak adolescent doses of ∼0.54 mSv y^-1. Application of the WHO flexibility level of 1 mSv y^-1 in adults (≈2 Bq L^-1) yields lifetime-averaged doses exceeding 2 mSv y^-1 and adolescent peaks approaching 5.4 mSv y^-1. These results demonstrate that adult-only assumptions systematically underestimate lifetime and age-specific ingestion doses for radionuclides with strong skeletal retention. Incorporating age-dependent intake and retention provides a more realistic basis for evaluating drinking-water radioactivity and supports the integration of lifetime-resolved modeling into radiological water-safety assessments.