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David Stavarek, R.G. June 29, 1998 Page 10 2. Conversion factors are not"probabilistic conversion factors." Delete from tables. 3. The following exposure factors may also be treated as stochastic PDFs: exposure frequency, fraction of body surface exposed in children and adults, skin surface area exposed in children and adults, soil ingestion in children and adults,tapwater ingestion rate in children and adults, produce ingestion rate in children and adults. 4. Body weight in adults. According to the Workplan,the"distribution" was truncated at the mean f 3 standard deviations (98%of the total AUC). According to this,the minimal weight of an adult is 38 kg (84 lbs). An"adult" with this weight should be considered a clinical case of severe malnutrition or famine. This mean body weight corresponds to boys and girls of 10 years of age. Please use the PDF data from the USEPA Exposure Factors Handbook, August 1997. Also see specific comments for Tables 2 and 6, below. 5. The inhalation rate PDF expressed as cubic meters per kilogram body weight per hour was taken from the CaITOX model. Normalizing inhalation rate for body weight has no biological basis, and is a conceptual error. Inhalation rate is NOT a direct function of body weight. but instead is mainly related to physical activitx. Other factors related to breathing rate include stress, environmental temperature, and sleep. Inhalation rate is regulated by several neuroendocrine factors, one of which is the partial pressure of CO2 detected by the baroreceptors. It can be said that"people breath in order to eliminate CO2 and incorporate 02 needed to burn calories." Therefore, the data developed by McKone and used in the CaITOX model (Cal/EPA, 1994) is wrong. As an analogy, it can be stated that inhalation rate cannot be normalized for the number of arms plus legs, or number of hair on the head, or the thickness of the adipose tissue in the upper arm, or the shoe size. These are only apparent correlates. Please use the scientific PDF data from the USEPA Exposure Factors Handbook, August 1997. 6. The skin surface area PDF expressed per kilogram body weight was taken from the CaITOX model. There is ample data showing that skin surface area is a function of weight and height. Therefore, the data developed by McKone and used in the CaITOX model is only partially correct. Please use the information from the USEPA Exposure Factors Handbook, August 1997. 7. The soil ingestion rate PDF expressed per kilogram body weight was taken from the CaITOX model. This is nonsense and has no scientific basis:people do not eat soil as a function of body weight. Therefore,the data developed by McKone and used in the CaITOX model is wrong. Please use the PDF data from the USEPA Exposure Factors Handbook, August 1997.