Soil Ingestion Distributions for Monte Carlo Risk Assessment in Children

Abstract

Monte Carlo environmental risk assessment requires estimates of the exposure distributions. An exposure of principal concern is often soil ingestion among children. We estimate the long-term (annual) average soil ingestion exposure distribution using daily soil ingestion estimates from children who participated in a mass-balance study at Anaconda, MT. The estimated distribution is accompanied by uncertainty estimates. The estimates take advantage of developing knowledge about bias in soil ingestion estimates and are robust. The estimates account for small particle size soil, use the median trace element estimate for subject days, account for the small sample variance of the median estimates, and use best linear unbiased predictors to estimate the cumulative long term soil ingestion distribution. Bootstrapping is used to estimate the uncertainty of the distribution estimates. The median soil 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 discussed for use of these estimates in Monte Carlo risk assessment.