Appendix B: Charge to the Panelists
The Agency for Toxic Substances and Disease Registry (ATSDR) scheduled this workshop to assess the current state of the science on soil-pica behavior--an issue that is relevant to ATSDR's ongoing work at sites with human exposure to contaminated soils. ATSDR intends to use the findings of this workshop to ensure that the agency continues to provide meaningful and scientifically defensible analyses of the potential health threats for individuals who exhibit soil-pica behavior.
During this workshop, ATSDR seeks expert opinions on several key questions, which are outlined below. Further, ATSDR welcomes insights on additional topics relevant to soil-pica behavior not explicitly addressed in the questions (see topic #4). Following the workshop, ATSDR will prepare a summary report to document the panelists'responses to these questions. The workshop discussions will focus on answering the questions that pertain to the following four topics:
Topic #1: The prevalence of soil-pica behavior. A key aspect of preparing public health assessments and consultations pertaining to soil-pica behavior is having a sense of the prevalence of this behavior among different groups. A review of the literature shows several types of methods used to characterize soil-pica behavior, such as analytical, observational, and questionnaire. Some studies were provided to you prior to the workshop that used these methods. Using these and other studies, ATSDR seeks the expert panel's inputs on the following questions:
• What observational, questionnaire, and analytical studies are most valid for characterizing the extent of soil-pica behavior?
• What is the prevalence rate of soil-pica behavior among children, especially preschool children? among adults? among pregnant women?
• 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.)?
• Within the various age categories, has the prevalence of soil-pica behavior been shown to be more common among any groups (e.g., urban or rural populations, ethnic groups, people of different socio-economic status)?
• Should ATSDR evaluate soil-pica behavior as an exposure scenario for hazardous waste sites or is soil-pica behavior too rare to be a public health concern?
Topic #2: Ingestion rates for soil-pica. The expert panelists were provided several scientific papers as well as the chapter from EPA's Exposure Factors Handbook that summarizes soil ingestion rates that have been reported for soil-pica children. The soil ingestion rates ATSDR uses are a critical input to the agency's public health evaluations. Please be prepared to respond to the following questions pertaining to soil ingestion rates:
• ATSDR currently assumes children who exhibit soil-pica behavior, on average, ingest 5 mg of soils per day. Based on your review of the literature on soil-pica behavior, is this soil ingestion rate scientifically defensible? Does this represent plausible exposures for children (i.e., is this soil ingestion rate unrealistically high or unrealistically low)? What soil ingestion rate would you recommend?
When evaluating children's exposure, ATSDR currently applies the soil ingestion rate of 5 mg per day for the entire duration of acute (<14 days), intermediate (14-365 days), and chronic exposures (>365 days) but may alter the frequency of the behavior depending on the duration of expected exposure. For example, ATSDR may assume a 1 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?
• 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?
Topic #3: Means for identifying people with soil-pica behavior. An important element of ATSDR's public health mission is to prevent unhealthy exposures to hazardous chemicals. Thus, the agency is interested in how health professionals and parents can identify children who exhibit soil-pica behavior. More specifically:
• ATSDR has reviewed studies that employed analytical, observational, and questionnaire techniques for identifying children who exhibit soil-pica behavior. What are the strengths and weaknesses of these methods? Are there other methods available to identify people with soil-pica behavior? Considering the pros and cons of each method, which method do you think ATSDR should use to identify people with soil-pica behavior?
Topic #4: Additional Topics
The panelists raised several issues when responding to the following final set of charge questions: "What critical research needs should be addressed to provide ATSDR greater insight into the public health implications of soil-pica behavior? What is known about the causes of soil-pica behavior? Does the bioavailability of metals in soil change with the amount of soil that is ingested? Is soil-pica behavior "normal"? Please bring to ATSDR's attention any other topics relevant to soil-pica behavior that are not addressed by the aforementioned questions.
When discussing the charge questions, please submit citations for references that ATSDR should consider when evaluating soil-pica behavior.