Biasing factors for simple soil ingestion estimates in mass balance studies of soil ingestion

Soil ingestion estimates from mass balance soil ingestion studies can be us ed in Monte Carlo Risk assessment. We develop and describe a simulation mod el based on four mass balance soil ingestion studies that enables food inge stion, soil ingestion, and transit time to be mimicked. We use the simulati on to evaluate potential biases that exist in current estimates of the dist ribution of daily soil ingestion in children (constructed from subject spec ific average daily estimates). The simulation identifies the importance of the study duration on the bias in the upper percentile soil ingestion estim ates, indicating that the 95% soil ingestion estimate may be positively bia sed by over 100%. Misspecification of play areas for soil sampling is shown to have no biasing effect, and absorption of trace elements in food of up to 30% is shown to bias the soil ingestion distribution by less than 20 mg/ d. The results, based on Al and Si trace element estimates, define the limi ts of previously published soil ingestion estimates, and provide insight fo r future study design and estimation methods.