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Toxicological Risks of Selected Flame-Retardant Chemicals
BMD5, benchmark dose for a 5% effect; RfD, reference dose; UFA, extrapolation from animals to humans; UFH, intraspecies variability.
aThe BMD5 was calculated using the data from both of these studies (Allen et al. 1996).
borate (3ZnO:2B2O3) (Lide 1991–1992). The RfD for zinc borate, based on the RfD for boron (0.34 mg boron/kg-d), would be approximately 3.0 mg zinc borate/kg-d. Zinc comprises approximately 51.2% (w/w) of zinc borate (3ZnO:2B2O3). The RfD for zinc borate, based on the RfD for zinc (0.3 mg zinc/kg-d), would be approximately 0.6 mg zinc borate/kg-d.
The oral RfD for zinc borate based on zinc is more conservative than the RfD for zinc borate based on boron. Therefore, the overall oral RfD for zinc borate is 0.6 mg zinc borate/kg-d, based on the RfD for zinc.
The subcommittee also considered the possibility of additive or synergistic effects between zinc and boron when assessing the risks associated with exposure to zinc borate. The main effects of boron are reproductive and developmental effects. Zinc has been shown to have reproductive effects in animals, but only at extremely high doses (≥200 mg Zn/kg-d). Effects other than reproductive and developmental have only been seen following exposure to boric acid at very high doses (≥1,000 ppm-d). The subcommittee concluded that additive or synergistic effects are not expected because of the lack of target overlap.
The subcommittee’s confidence in the zinc RfD is medium. The lack of data on the parent compound makes the overall confidence in the oral RfD (0.6 mg zinc borate/kg-d) low.
Cancer
The potential carcinogenicity of zinc borate, zinc oxide, and boric acid cannot be determined because of inadequate carcinogenicity data from any route of exposure.
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