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3 Exposure Assessment Methodology
Pages 35-52

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From page 35...
... Second, for most of the FRs evaluated, only limited toxicity information is available for the oral route of exposure, and even less is available for the inhalation route. For the dental route, the minimal toxicity information that is available is not adequate for developing dermal reference doses.
From page 36...
... The subcommittee believes that pesticides are not good surrogates for FR chemicals. To make progress, therefore, the subcommittee adopted some extremely conservative assumptions (that is, corresponding to high concentration and exposure conditions)
From page 37...
... In the first iteration, the release rate was the only limiting factor and any chemical on the skin was assumed to completely transfer within the body and chemicals that would not cause health concerns under this scenario were eliminated from further calculations. For the remaining chemicals, an estimate of the transfer across the skin was used to estimate the internal dose and the hazard index.
From page 38...
... Under the exposure conditions described above, the dose rate for the dermal route for FRs is calculated using Equation I: D = SaAb~wfc Ma where the meanings and values assigned to the symbols are as follows: D = The dose rate of chemical (mass of chemical per unit body weight per unit time)
From page 39...
... The rate of penetration of a chemical through skin may be estimated using the skin permeability coefficient (Kp, with dimensions of velocity~the total mass penetration rate is the product of water concentration, permeability coefficient, and skin area. Such coefficients have not been measured for the FR chemicals, but they may be estimated from the octanol-water partition coefficient (KoW, dimensionless)
From page 40...
... Using the permeability coefficient, the dose rate for the dermal route (alternative iteration) is obtained using Equation 3: CWKpAbfc D= Ha where the meanings and values assigned to the symbols are the following: (3)
From page 41...
... The assumption that the exposure occurs daily for a lifetime is also very conservative, and it assumes no deviation from the exposure for any reason. The most conservative assumptions in calculating hazard indices are that the constant release rate of FRs is for the life of the fabric, permeability coefficients are probably overestimated for the high-molecular-weight chemicals, the applied chemicals do not react in the fabric, and there is no attempt to limit the exposures by the actual amount of chemical in the fabric.
From page 42...
... Toxicity based on oral studies for chemicals that might have been incompletely absorbed would underestimate risk by the dermal route when the hazard index was calculated. INHALATION EXPOSURE SCENARIO Particles In the inhalation exposure scenario, a person spends some fraction of his or her time in a room containing Fit-treated upholstered furniture.
From page 43...
... Such concentrations may be compared with typical total indoor air concentrations of respirable particles on the order of 100 ,ug/m3 (EPA 1996~. From the average indoor concentration, a time-averaged exposure concentration for a person using the room was estimated using Equation 6: Cp avg = CPfi (6)
From page 44...
... For each FR, the time-average exposure concentration was divided by the provisional inhalation RfC derived from the chemical's oral RfD in order to calculate a hazard index. When necessary, the estimated RfC was calculated using Equation 7: W RfC = RfD a fib where the meanings and values assigned to the symbols are the following: (~7)
From page 45...
... . For all the FR chemicals, this value is assumed to be zero, because the air entering the room is not expected to be contaminated with the FR vapor.
From page 46...
... where the meanings and values ofthe symbols are as previously assigned. The time for which this equilibrium vapor concentration could be maintained within the room, before all the FR originally applied to the fabric evaporates may be calculated using Equation 11: / CVDa ( ;7~;v - ~ )
From page 47...
... With the other parameter values used, estimates of FR concentration are relatively insensitive to the exact value chosen for the boundary-layer thickness or to the diffusivities of the individual FRs—evaporation is principally limited by the room air-exchange rate. From the equilibrium vapor concentration in room air, the short-term timeaverage vapor exposure concentration was estimated using Equation 12: Cs avg = Cfi where the meanings and values assigned to the symbols are the following: Cs,avg = (12)
From page 48...
... For those FRs considered to be possibly carcinogenic, an overestimate of lifetime risk was obtained by multiplying the Tong-term time-average vapor exposure concentration by the inhalation unit risk for the chemical. If an inhalation unit risk was not available, the unit risk was estimated from the oral carcinogenic potency by using Equation 14: U = q Ma where the meanings and values assigned to the symbols are the following: (14)
From page 49...
... The most conservative assumptions relating to the inhalation exposure scenario are that vapor and particles will be released uniformly for the duration of the exposure and the ratio of room volume to fabric surface area. The most conservative assumptions in the calculation of hazard indices are constant release rate for the life of the fabric, complete absorption from the breath, the assumption that applied chemicals did not react in the fabric, no attempt to limit the exposures by the actual amount of chemical in the fabric, and no attempt to limit the vapor concentration by the actual achievable air concentration.
From page 50...
... For those FRs considered to be possibly carcinogenic, the lifetime average dose rate was calculated by taking into account the period during which a child might continue sucking behavior. The lifetime average dose rate was calculated using Equation 16: Da e = D- s (16)
From page 51...
... The subcommittee believes that actual exposures are likely to be at least 1 00-fold Tower than calculated, given the conservative nature ofthe estimation procedure. The most conservative assumptions relating to the oral exposure scenario are the surface area sucked, and that this would occur daily for two years.
From page 52...
... 1995. Residential air exchange rates in the United States: Empirical and estimated parametric distributions by season and climactic region.


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