3.5 Temporal Factors

The next question was: "What temporal factors in the prevalence of soil-pica behavior should ATSDR consider (e.g., does soil-pica behavior generally occur once a week, three times a week, etc.)?" After a brief discussion, the panelists agreed that the existing soil ingestion studies--nearly all of which evaluated children's behavior for durations of 2 weeks or shorter--are inadequate for determining the frequency of, and seasonal variations in, soil-pica behavior.

Before reaching this conclusion, several panelists commented on the extent to which temporal variations have been considered in previous soil ingestion studies. One panelist noted that his surveys of parents in Rochester, New York, did not ask them how frequently their children ingest soils (BL). Another panelist said her surveys also focused on whether children ingest soils, but not how often (NF). Reiterating a comment made earlier, this panelist found that surveys are poor methods for accurately quantifying detailed information about children's behavior, such as how often they ingest soils. Thus, the panelists suggested that the available soil ingestion survey data do not characterize the frequency of soil ingestion.

Other panelists commented that analytical data do not adequately characterize temporal variations in soil ingestion. For instance, two panelists indicated that none of the analytical studies examined soil ingestion for durations longer than 4 months and that most studies lasted only 2 weeks or less (SD, DM). Another panelist noted, however, that Ed Calabrese's analytical study does demonstrate considerable day-to-day variability in soil ingestion rates, but he questioned how representative this variability is of children nationwide (RW). Overall, panelists agreed that the analytical studies do not address seasonal variations in soil ingestion--a factor they thought would be important in evaluating soil ingestion, particularly for regions with cold winters. Consistent with this argument, one panelist indicated that blood lead levels among children he has studied in Rochester, New York, tend to peak during the summer (BL).

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