Soil ingestion in adults--results of a second pilot study

Soil ingestion was evaluated in 10 adults as part of a larger study to evaluate soil ingestion in children. Each adult was followed for 4 weeks in a mass-balance study that was designed to evaluate the detection limit for soil ingestion in a similarly designed, concurrent children's study. After a baseline week, during Weeks 2 through 4, adults received daily soil capsules containing 20, 100, and 500 mg of soil, respectively. A 1-week period separated each study week. Based on the first 3 weeks of observation after subtracting the capsule ingestion amounts, the median, 75th percentile, and 95th percentile soil ingestion estimates were 1, 49, and 331 mg/day, with estimates calculated as the median of the three trace elements Al, Si, and Y. The average estimate of soil ingestion was 10 mg/day (SD = 94 mg/day). These findings augment sparse empirical data on adult soil ingestion, and suggest lower levels of soil ingestion in adults than previous studies.