Soil ingestion - A concern for acute toxicity in children (Reprinted from Environmental Health Perspectives, vol 105, Dec, 1997)

Several soil ingestion studies have indicated that some children ingest sub stantial amounts of soil on given days. Although the U.S. Environmental Pro tection Agency (U.S. EPA) has assumed that 94 percent of children ingest 20 0 mg of soil per day or less for exposure assessment purposes, some childre n have been observed to ingest up to 24 to 60 g of soil during a single day . In light of the potential for children to ingest such large amounts of so il, an assessment was made of the possibility for soil pica episodes to res ult in acute intoxication from contaminant concentrations U.S. EPA regards as representing conservative screening values (i.e., U.S. EPA soil screenin g levels and U.S. EPA Region III risk-based concentrations for residential soils). For a set of 13 chemicals included in the analysis, contaminant dos es resulting from a one-time soil pica episode (5 to 50 g of soil ingested) were compared with acute dosages shown to produce toxicity in humans in cl inical studies or case reports. For four of these chemicals, a soil pica ep isode was found to result in a contaminant dose approximating or exceeding the acute human lethal dose. For five of the remaining chemicals, the conta minant dose from a soil pica episode was well within the reported dose rang e in humans for toxicity other than lethality, Because both the exposure ep isodes and the toxicological response information are derived from observat ions in humans, these findings are regarded as particularly relevant for hu man health risk assessment. They suggest that, for some chemicals, ostensib ly conservative soil criteria based on chronic exposure using current U.S. EPA methodology may not be protective of children during acute soil pica ep isodes.