Estimates of Hourly Dust and Soil Ingestion Rates for Children and Adults In- and Outdoors

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ISEE-217 Objective: Daily soil and dust ingestion rates are often estimated using tracer studies. Information on the contribution of dust in the total soil and dust ingestion is often lacking. However, in view of the large contribution of indoor contaminants in the total exposure, this information is essential. Therefore, a mathematical model was developed that uses estimates of daily soil and dust ingestion rates from tracer studies, the fractions spend in- and outdoors and the indoor/outdoor ingestion ratio as input variables. Material and Methods: The average (±SD) daily soil and dust ingestion rates calculated from published tracer studies ranged between 71.8 ± 12.01 and 41.67 ± 10.32 mg/d for children and adults, respectively. For the Monte-Carlo simulations (5000 iterations) soil and dust ingestion was assumed to be log-normally distributed. The indoor/outdoor ingestion ratio was assumed to be uniformly distributed between 0.1 and 1.0 for children and between 0.3 and 1.0 for adults. A triangular distribution between 1 and 6 hours, with a most likely value of 3 hours was chosen for the time spent outside, both for children and adults. Results: Average hourly soil ingestion rates [corresponding with a central tendency exposure scenario (CTE)] for children outdoors and indoors of 13.55 and 3.28 mg/h were calculated. The average hourly dust ingestion inside was estimated as 3.44 mg/h. Corresponding estimates under a reasonable maximal exposure scenario (RME = 95th percentiles from simulations) for soil outdoors, indoors, and dust indoors were 22.52, 5.48, and 6.94 mg/h, respectively. For adults, these values were 5.78 (soil outdoors), 1.78 (soil indoors), and 1.90 mg/h (dust indoors) under a CTE scenario and 12.94 (soil outdoors), 3.83 (soil indoors), and 4.69 mg/h (dust indoors) under an RME scenario. Conclusions: Hourly ingestion rates for soil and dust allow the risk assessor to predict exposure to soil-borne pollutants for a particular setting and duration, more accurately.