Life-stage-resolved screening of inhalation exposure to PM_2.5-bound elements in Nonthaburi, Greater Bangkok, Thailand

Mass-based PM_2.5 regulation does not identify which particle-bound elements determine toxicological priority. This fixed-site secondary-data study evaluated scenario-based pediatric life-stage exposure using a single ambient PM_2.5-bound elemental dataset and literature-derived exposure parameters. Seasonally weighted annual outdoor inputs were derived from selected 24-h filter-sampling days during December 2020-September 2021 and combined with indoor penetration, time-activity, respiratory deposition, and simulated-lung-fluid (SLF) solubility assumptions. The noncancer analysis prioritized element-specific respiratory-deposited intake, followed by an SLF-solubility-adjusted profile. Mixed-benchmark comparative priority quotients (CPQs) were used for exploratory within-study ranking. The annual concentration and respiratory-deposited intake profiles were highest for Al, Fe, B, and Zn, whereas the CPQ ranking prioritized As, Cd, and Sb under the selected SLF and toxicity-reference assumptions. The primary modeled lifetime cancer-risk estimate, based on Cr(VI)-equivalent chromium, As, and Cd, ranged from 1.11 × 10^-6 at 0% Cr(VI) to 2.78 × 10^-5 at 100% Cr(VI). The corresponding conservative Ni-inclusive sensitivity ranged from 1.22 × 10^-6 to 2.79 × 10^-5. These results support within-model prioritization at one fixed site and do not represent measured child exposure or province-wide risk.