4.2 Applying Ingestion Rates to Acute, Intermediate, and Chronic Exposure

The second charge question pertaining to soil ingestion rates, was: "When evaluating children's exposure, ATSDR currently applies the soil ingestion rate of 5,000 mg per day for the entire duration of acute (<14 days), intermediate (14-365 days), and chronic exposures (>365 days) to develop screening levels. However, when evaluating site-specific residential exposures, ATSDR may alter the frequency of the behavior depending on the duration of expected exposure. For example, ATSDR may assume a one time exposure or 3 days of exposure per week for several weeks, depending on site-specific conditions and toxicology of the contaminant of concern. Is this approach valid? What would you recommend in varying the amount and frequency of soil ingested over time? Are data available to support use of age-specific ingestion rates for soil-pica children?"

Because most of the analytical studies of soil ingestion spanned 2 weeks or less and none lasted over 4 months, the panelists agreed that soil ingestion rates over intermediate and chronic exposure durations have yet to be characterized. One panelist noted that extrapolations of short-term analytical studies to long-term exposure scenarios suggest that few children likely ingest 5,000 mg of soil a day throughout a year (PS). Specifically, he explained that a statistical review of an analytical study has suggested that the likelihood of children ingesting 5,000 mg of soil every day of the year is extremely low (<1%) (Calabrese and Stanek, 1998). However, this panelist and others stressed that no long-term studies have been conducted to verify this finding.

The panelists did not explicitly answer the question of whether or not assuming children ingest 5,000 grams of soil, 3 days a week, was a reasonable assumption, because there is limited data upon which to base this assumption.

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