Toxicological Risks of Selected Flame-Retardant Chemicals (2000) / Chapter Skim
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8 Zinc Borate
8 Zinc Borate
Pages 149-191
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From page 149... ...
The subcommittee also identified date gaps andrecommended research relevant for determining the health risk from exposure to zinc borate. PHYSICAL AND CHEMICAL PROPERTIES The physical and chemical properties of zinc borate, zinc oxide, and boric acid are summarized in Table 8-1.
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From page 150... ...
Zinc borate is used as a flame retardant
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TOXICOKINETICS Absorption Zinc Borate No studies were identified that investigate the toxicokinetics of zinc borate following dermal, inhalation, or oral exposure. Zinc Oxide Agren (1991)
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From page 152... ...
study, the swallowing of zinc particles during grooming activities might also account for the increased tissue zinc levels. No data are available on the oral absorption of zinc oxide.
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1994~. Metabolism and Distribution Zinc Borate Zinc borate is metabolized to zinc oxide and boric acid prior to being absorbed.
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Excretion Zinc Borate No data were identified that investigated the excretion of zinc borate in humans or animals following any route of exposure. Zinc Oxide No studies were identified that investigated the excretion of zinc in humans or animals following dermal application of any zinc compounds.
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From page 155... ...
. Zinc Oxide There are two case studies in the literature that suggest that Berman occupational exposure to zinc oxide might cause or contribute to a skin condition iIn this section, the subcommittee reviewed toxicity data on zinc borate, including the toxicity assessment prepared by the U.S.
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From page 156... ...
for 5 consecutive clays with zinc oxide (20% suspension in Tween 80) , zinc chloride (~°/0 aqueous solution)
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From page 157... ...
Boric Acid No studies were found on the systemic effects of boric acid following dermal absorption. Other Systemic Effects No studies were found that investigated the immunological, neurological, reproductive, developmental, or carcinogenic effects of zinc borate, zinc oxide, or boric acid following dermal exposure in humans or experimental animals.
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From page 158... ...
Deficits in lung function were seen in guinea pigs exposed to zinc oxide dust (3.7-5.6 me zinc/m3)
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From page 159... ...
following exposure to a low dose of zinc oxide fumes. The symptoms reappeared in a challenge test, suggesting a sensitization to zinc compounds.
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(1988) found that female mice, but not female rats or guinea pigs, exposed to ~ .3, 12.S, or 121.7 mg zinc /m3 as zinc oxide/hexachioroethane
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From page 161... ...
Other Systemic Effects No studies were found that investigated the neurological effects of zinc oxide and boric acid following inhalation exposure. Oral Exposure Systemic Effects Zinc Borate U.S.
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From page 163... ...
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From page 166... ...
Serum zinc levels were significantly increased in the exposed group after 2 wk. No oral LDso value has been reported for zinc oxide, but LDso values for other zinc compounds range from 237 to 623 mg zinc/kg-d in rats, and 86 to 390 mg zinc/kg-d in mice.
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From page 167... ...
. Administration of boric acid in the diet reduced weight gain and affected nucleotide levels in numerous tissues in rats treated with 10,000 ppm (500 mg boron/kg- for 21-27 ~ (Dani et al.
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From page 168... ...
Doses above 26.3 mg boron/kg-d decreased growth and food consumption. Body weights and some organ weights were altered at 26.3 mg boron/kg-d in females, and were consistently altered at the higher dose levels.
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From page 169... ...
There were no apparent effects on appearance, behavior, appetite, body weight, or food consumption. Organ weights and organ weight to body weight ratios were not changed from control levels, and the hematological and biochemical values in the treated animals were within the normal range of values.
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Testicular atrophy (controT 3/49; low dose, 6/50; high dose, 27/47; at 0, 2,500, and 5,000 ppm boric acid) and interstitial cell hyperplasia
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From page 171... ...
Reproductive and Developmental Effects Zinc Borate No studies on the reproductive or developmental effects of zinc borate following oral exposure were identified. Zinc Oxide In humans, no developmental effects were reported in newborns following ingestion of zinc compounds by mothers during the last two trimesters of pregnancy (Kynast and Sating 1986; Mahomed et al.
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From page 172... ...
Fetal body weight was decreased in a dose-dependent manner, with significant decreases seen at all doses. Significant fetal malformations, including effects on the eyes, central nervous system, cardiovascular system, and axial skeleton, occurred at and above 28.5 mg/kg-d.
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had a dose-dependent decrease in fetal body weight, with statistically significant decreases at the two highest doses. increased skeletal malformations also occurred at those doses.
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Cancer Zinc Borate No studies were located that investigated the carcinogenicity of zinc borate following oral exposure. Zinc Oxide Two epidemiological studies report conflicting results on the association between high zinc soil levels and cancer.
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NTP concluded that there was no evidence of carcinogenicity for boric acid (NTP 1987~. Gen oto xi city Zinc Borate Zinc borate was not mutagenic in the Ames Salmonella mutagenicity bioassay, with or without metabolic activation (U.S.
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From page 176... ...
Inhalation exposure of mice to zinc oxide induced chromosomal aberrations in bone marrow cells, but no exposure concentrations were given (Voroshilin et al. 1978; as cited in ATSDR 1994~.
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ZINC BORATE I 77 Boric Acid The weight of evidence indicates that boron compounds are not genotoxic (Table 8-4~. TABLE 8-4 Genotoxicity of Boron Compounds Boron Genotoxicity Test System Compound End Point Result Reference Escherichia cold Boric acid Gene mutations Positive Demerec et Blr/Scl-4 al.
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Oral RfD There are inadequate oral toxicity data on zinc borate to derive an oral RfD. However, zinc borate readily breaks down in the stomach to zinc oxide and boric acid.
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From page 179... ...
Zinc Borate In order to derive an oral RfD for zinc borate from the RlDs for zinc compounds and boric acid, the relative contributions of zinc and boron to zinc borate were determined. Boron comprises approximately 11.3% (w/w)
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From page 180... ...
Fetal weight Spragueaveraged within Dawley rats litters UFA 3 UFH 1 O Total: 30 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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From page 181... ...
, and Equation 1 in Chapter 3, the subcommittee calculated a dermal exposure level of 6.3 x 10-3 mg/kg-~. The oral RfD for zinc borate (0.6 mg/kg-~; see Oral RfD in Quantitative Toxicity section)
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From page 182... ...
~ x 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.
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DATA GAPS AND RESEARCH NEEDS There are little toxicity data available for zinc borate. Once in the body, zinc borate readily breaks down to zinc oxide and boric acid.
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From page 184... ...
Gill.1982. Respiratory response of guinea pigs to zinc oxide fume.
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From page 185... ...
Casualties following exposure to zinc chloride smoke. Lancetii:368370.
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From page 186... ...
1999. Toxicity review for zinc borate.
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From page 187... ...
Amdur.1982. Changes in lung volumes and diffi~sing capacity in guinea pigs exposed to a combination of sulfur dioxide and submicron zinc oxide mixed in a humidif~ed furnace.
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1988. Pulmonary function of guinea pigs exposed to freshly generated ultrapure zinc oxide with and without spike concentrations.
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Metal-fume fever frominhaling zinc oxide.
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From page 190... ...
An occupational dermatoconiosis among zinc oxide workers. Public Health Rep.36:2727-2732.
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From page 191... ...
1998. In viva percutaneous absorption of boric acid, borax, and disodium octaborate tetrahydrate in humans compared to in vitro absorption in human skin from infinite and finite doses.
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