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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. after application of a commercial talcum powder containing 5% boric acid (Mulinos et al. 1953, as cited in Moore 1997; Vignec and Ellis 1954, as cited in IPCS 1998). In rabbits, intact skin acts as a barrier to dermal absorption of boric acid, whereas absorption was much greater through damaged skin (Draize and Kelly 1959). In an in vitro absorption assay, 0.05%, 0.5%, or 5% boric acid solution were applied to human skin, and 1.2%, 0.28%, and 0.7%, respectively, of the boric acid was absorbed (Wester et al. 1998). From those data, flux values of 0.25, 0.58, and 14.58 µg/cm2/hr, and permeability constants (Kp) of 5.0×10−4, 1.2 ×10−4, and 2.9×10−4 cm/hr for the 0.05%, 0.5%, and 5.0% boric acid solutions, respectively, were calculated (Wester et al. 1998). In contrast to the lack of dermal absorption, boric acid is readily absorbed following inhalation and oral exposure. Kent and McCance (1941, as cited in Moore 1997) demonstrated in two female subjects that at least 90% of ingested boric acid is absorbed and excreted in the urine. More recently, Jansen et al. (1984) demonstrated greater than 90% recovery of administered boron in the urine of six male volunteers following ingestion of boric acid. An occupational study of workers involved in packaging and shipping borax (Na2B4O7• 10H2O) showed elevated boron levels in the urine after inhalation exposure (Culver et al. 1994). Metabolism and DistributionZinc BorateZinc borate is metabolized to zinc oxide and boric acid prior to being absorbed. Zinc OxideNo relevant human or animal studies were identified that investigated the distribution of zinc following dermal exposure to zinc compounds. No inhalation exposure studies were identified that investigated the distribution of zinc compounds in humans. Cats exposed to zinc oxide fumes (12–61 mg Zn2+/kg-d) for 3 hr had increased zinc levels in the pancreas, liver, and kidneys (Drinker and Drinker 1928, as cited in ATSDR 1994), however, oral absorption through swallowing or grooming cannot be ruled out. There are no data on the metabolism and distribution of zinc oxide following oral exposure. Weigand and Kirchgessner (1992) demonstrated that more zinc is distributed to the kidneys and pancreas than to the liver in rats fed 1.1 mg
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