A Multitracer Reconciliation Approach for Estimating Child-Specific Dust and Soil Ingestion Rates

Reliable quantification of children's ingestion of dust and soil is essential for accurate exposure and risk assessment. Yet, most existing estimation strategies, typically relying on a single tracer element or evaluating multiple tracers independently, suffer from measurement uncertainties, the burdensome collection of excreta volumes, incomplete accounting of exposure and elimination pathways, reliance on population-average assumptions, and the inability to distinguish dust ingestion from soil ingestion. To address these limitations, we develop a novel "multitracer" reconciliation approach that estimates individual-level ingestion rates of dust and soil particles by jointly using concurrent measurements of multiple elements in dust, soil, urine, and fecal samples and mathematically identifying the physiologically plausible solution that best satisfies all tracer-specific mass-balance equations simultaneously. This approach supports deriving personalized dust and soil ingestion rates that maintain physiological plausibility while minimizing inconsistencies across tracers. Applied to 112 U.S. children representing diverse demographic backgrounds, our approach produced estimates of dust, soil, and "combined" dust and soil ingestion rates (medians: 38, 10, and 75 mg/day, respectively; the sum of dust and soil medians differs from the "combined" median because individual children had varying relative contributions from dust and soil). These estimates agree with reference values provided in the U.S. EPA's Exposure Factors Handbook. Ingestion patterns varied with age, season, race/ethnicity, and body-mass-index category. This multitracer reconciliation framework provides a data-driven foundation for reducing uncertainty in exposure factors and refining child-specific risk characterization.