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The following HTML text is provided to enhance online readability. Many aspects of typography translate only awkwardly to HTML. Please use the page image as the authoritative form to ensure accuracy. 2.3×10−7/d. Using those values, the estimated time-averaged exposure concentration for zinc borate is 0.19 µg/m3. Although lack of sufficient data precludes deriving an inhalation RfC for zinc borate, the oral RfD (0.6 mg zinc borate/kg-d; see Oral RfD in Quantitative Toxicity section), which represents a conservative estimate, was used to estimate an RfC of 2.1 mg/m3 (see Chapter 4 for the rationale). Division of the exposure concentration (0.19 µg/m3) by the estimated RfC (2.1 mg/m3) results in a hazard index of 9.1×10−5. Therefore, the subcommittee concluded that, under the worst-case exposure scenario, exposure to zinc borate particles from its use as an upholstery fabric flame retardant is not likely to pose a noncancer risk. VaporIn addition to the possibility of release of zinc borate in particles worn from upholstery fabric, the subcommittee considered the possibility of its release by evaporation. However, because of zinc borate’s negligible vapor pressure at ambient temperatures, the subcommittee concluded that exposure to zinc borate vapors from its use as an upholstery fabric flame retardant is not likely to pose a noncancer risk. Oral ExposureThe assessment of the noncancer risk by the oral exposure route is based on the scenario described in Chapter 3. The exposure assumes a child is exposed to zinc borate through sucking on 50 cm2 of fabric, backcoated with zinc borate, daily for two yr, one hr/d. The highest application rate for zinc borate is 2 mg/m2. A fractional rate (per unit time) of zinc borate extraction by saliva is estimated as 0.001/d, based on leaching of antimony from polyvinyl chloride cot mattresses (Jenkins et al. 1998). Using those assumptions in Equation 15 in Chapter 3, the average oral dose rate was estimated to be 0.00017 mg/kg-d. Division of that exposure estimate (0.00017 mg/kg-d) by the oral RfD (0.6 mg/kg-d; see Oral RfD in Quantitative Toxicity Assessment Section) results in a hazard index of 2.8×10−4. Therefore, under the worst-case exposure assumptions, zinc borate, used as a flame retardant in furniture-upholstery fabric, is not likely to pose a noncancer risk by the oral route of exposure.
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