ARCHIVED REPORTS_ROY'S AUTO - HISTORICAL (2)

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The second decision is to use the 'b#�rst available tool for assessing the relationship between children' s blood lead levels and environmental lead levels . Current research indicates that young children are particularly sensitive to the effects of lead and require specific attention in the development of lead standards . A level that is protective for young children is expected to be protective for older population subgroups . In the same environmental setting, pregnant women would be expected to have blood lead levels lower than would young children, and this may further limit fetal exposures . The Agency has examined both epidemiological studies and modeling approaches for this purpose. Both of these will be further evaluated as part of the effort to develop section 403 rulemaking. However, given the need to issue guidance at this time , the Agency is choosing to base the guidance on the Integrated Exposure Uptake Biokinetic (IEUBK) model , which EPA designed to evaluate exposures to children in a residential setting . In general the model generates a probability distribution of blood lead iavels for a typical child, or group of children, exposed to a particular soil lead concentration and- concurrent lead levels from other sources . The spread of the distribution reflects the observed variability of blood lead levels in several communities . This variability arises from several sources, including behavioral and cultural factors . The identification of lead levels from other sources (due to air, water, diet, etc. ) is an essential part of characterizing the appropriate blood lead distribution for a specific neighborhood or site . For the purpose of deriving the 400 ppm value used in this guidance, the background lead exposure inputs to the IEUBK model were determined using national averages, where suitable, or typical values . Thus, the estimated level of 400 ppm is associated with an expected "typical" response to these exposures, and should not be taken to indicate that a certain level of risk (e.g. , exactly 5%; of children exceeding 10 pg/dl blood lead) will be observed in a specific community (e. g. , in a blood lead survey) . Because a child' s exposure to lead involves a complex array of variables, because there is population sampling variability,__ and because there is variability in environmental lead measurements and background levels of lead in food and drinking water, results from the model may differ from results of blood lead screening of children in a community. Extensive field evaluation of the model is in progress and- the model will be evaluated further once these efforts are completed. EPA may base the future section 403 rulemaking on the model once these 10