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4.3 Ingestion Rates for Adults Who Exhibit Soil-pica Behavior

Historical Document

This Web site is provided by the Agency for Toxic Substances and Disease Registry (ATSDR) ONLY as an historical reference for the public health community. It is no longer being maintained and the data it contains may no longer be current and/or accurate.

The final charge question on soil ingestion rates was: "Are sufficient data available for establishing a scientifically defensible soil ingestion rate for adults who exhibit soil-pica behavior? If so, what soil ingestion rate do you recommend?" Referring to their earlier discussions on geophagy among adults, the panelists noted that adults who consume large quantities of soils or clays tend to obtain these materials from known, uncontaminated sources. Having heard anecdotal accounts of a small number of adults who might consume soils from contaminated sources, however, the panelists recommended that ATSDR view soil-pica among adults as an extremely rare behavior, but not so rare as to be ruled out of consideration. The panelists recommended that ATSDR investigate soil-pica in adults when that behavior has been shown to occur in people who live on or near a site that the agency is investigating. The panelists unanimously agreed that soil ingestion rates among pica adults have never been characterized.

Table 4-1

Data on Soil-Pica Discussed by the Panelists

Evidence of Soil-Pica Published by Ed Calabrese and Ed Stanek

During a study of 64 preschool children in Amherst, Massachusetts, soil-pica was observed on two occasions:

  • A 2 ½- year-old girl was observed for 4 days. On two of these days, she ingested 20,000 mg and 22,000 mg of soil.
  • A young girl ingested between 1,000 mg and 2,000 mg of soil on 4 days of a 7-day period.

Evidence of Soil-Pica Published by Michael Wong

During a 4-month study of 24 children (average age 3.1 years) living in a long-term government supervised institution in Jamaica, soil-pica was observed in five children:

  • Child #1 ingested 1,447 mg of soil on 1 day
  • Child #2 ingested 7,924 mg of soil on 1 day
  • Child #3 ingested 1,016 mg of soil, 2,690 mg of soil, and 898 mg of soil on different days
  • Child #4 ingested 10,343 mg of soil, 4,222 mg of soil, and 1,404 mg of soil on different days
  • Child #5 ingested 5,341 mg of soil on 1 day.

In addition, during a study of 28 older children (average age 7.2 years), soil-pica was observed in one child who was developmentally disabled. This child ingested 48,300 mg of soil, 60,692 mg of soil, 51,422 mg of soil, and 3,782 mg of soil on different days.

Note: Of the soil ingestion rates listed in this table for preschool children, the median soil ingestion rate is 2,000 mg and the average value is 5,000 mg. One panelist noted that the soil ingestion study published by Michael Wong does not clearly state the nature and severity of the developmental disability in the child who ingested large quantities of soil (NF). As a result, she was not sure if this child's behavior would be expected to occur among other individuals who have various types of developmental disabilities.

Table 4-2

Estimated Percent of Children with Soil Ingestion Exceeding Daily

Rates for Given Time Periods Per Year

Estimated Number of Days per Year with Soil Ingestion Rate

Daily Rate of Soil Ingestion (in mg)

> 200 > 500 > 1,000 > 5,000 > 10,000
1-2 86 72 63 42 33
7-10 72 53 41 20 9
35-40 42 31 16 1.6 1.6

Note: Data reproduced from Table 4 in Calabrese and Stanek, 1998.

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