Soil ingestion distributions for Monte Carlo risk assessment in children

Monte Carlo environmental risk assessment requires estimates of the exposur e distributions. An exposure of principal concern is often soil ingestion a mong children. We estimate the long-term (annual) average soil ingestion ex posure distribution using daily soil ingestion estimates from children who participated in a mass-balance study at Anaconda, MT. The estimated distrib ution is accompanied by uncertainty estimates. The estimates take advantage of developing knowledge about bias in soil ingestion estimates and are rob ust. The estimates account for small particle size soil, use the median tra ce element estimate for subject days, account for the small sample variance of the median estimates, and use best linear unbiased predictors to estima te the cumulative long term soil ingestion distribution. Bootstrapping is u sed to estimate the uncertainty of the distribution estimates. The median s oil ingestion is estimated as 24 mg/d (sd = 4 mg/d), with the 95 percentile soil ingestion estimated as 91 mg/d (sd = 16.6 mg/d). Strategies are discu ssed for use of these estimates in Monte Carlo risk assessment.