Limitations, dermal absorption

Hexachloroethane has been found in the plasma of workers wearing protective clothing and respiratory protection suggesting that hexachloroethane can be absorbed following inhalation and/or dermal exposure. Based on the minimal effects seen on target tissues (liver and kidney) in animal studies, absorption from the lungs seems to be limited. Dermal absorption was also estimated to be low based on calculated dermal penetration rates. 

Data regarding the absorption of radon following dermal exposure are very limited. Dermal absorption of radon has been measured in subjects after bathing in a radon-water spa (Furuno 1979 Pohl 1965) or after application of a radon-containing ointment to the intact skin (Lange and Evans 1947). After bathing for 5 to 15 minutes, radon-222 concentrations in expired air reached... 

A study with a dog exposed to an occluded dermal dose of TOCP labeled with radioactive phosphorus provides limited evidence that organophosphate esters in hydraulic fluids may be widely distributed after dermal absorption (Hodge and Sterner 1943). Similar widespread distribution of radioactivity among tissues was observed in male cats after dermal exposure to [uniformly labeled 14C-phenyl]TOCP (Nomeir and Abou-Donia 1986). Tissues and fluids with the highest concentrations of radioactivity in these studies included the bile, gall bladder, urinary bladder, liver, kidney, and fat, thus suggesting that TOCP and metabolites are somewhat preferentially distributed to these tissues. 

Limited information was located regarding dermal absorption of inorganic lead in animals. An early study reported that lead acetate was absorbed from the clipped skin of rats, as determined by an increase in the concentration of lead in the kidneys relative to controls (Laug and Kunze 1948). It was further shown in that study that mechanical injury to the skin significantly increased the penetration of lead and that the penetration of lead from lead arsenate was significantly less than from lead acetate. 

Hexachloroethane caused reversible corneal injury in rabbits following ocular contact, but contact with the skin for 24 hours resulted in no dermal effects (Weeks et al. 1979). The physical properties of hexachloroethane suggest that absorption across human skin would be limited (Fiserova-Bergerova et al. 1990). Therefore, unless dermal absorption studies indicate that this prediction is incorrect, there is no need for additional studies of acute dermal toxicity. 

Data are very limited regarding absorption of 1,3-DNB following dermal exposure in humans. Evidence of dermal absorption was found in an early report in which an experimenter became cyanotic after self-applying an ointment containing 25% (w/w) 1,3-DNB (White and Hay 1901). Similar findings were described in a case of a woman exposed to a solution containing 0.5% (w/w)... 

Humans may be exposed to 2,3-benzofuran by inhalation, ingestion, or dermal absorption. Based on the limited data available, exposure of the general population to 2,3-benzofuran does not appear to be substantial. However, since this compound has been detected at hazardous waste sites, is reported to be a component of cigarette smoke, and is one monomer in a resin which may be used as a coating on citrus fruits and in packaging materials for foods, human exposure may be possible from these sources. People in Britain who had died in fires had 2,3-benzofuran in some blood samples, but no source of exposure was identified (Anderson and Harland 1980). 2,3-Benzofuran was... 

Polybrominated Diphenyl Ethers. No information was located regarding dermal absorption of PBDEs in humans. The only information regarding dermal absorption in animals is that from a study of absorption in an in vitro preparation (Hughes et al. 2001). In that study, " C-dccaBDE dissolved in tetrahydrofuran was applied to dorsal skin (three dose levels) excised from adult hairless female mice and fractions of receptor fluid were collected over a 24-hour period. Transfer of radioactivity to the receptor fluid was minimal, only 0.07 to 0.34% of the applied radioactivity. Two to 20% of the radioactivity was found in the skin, and the lowest dose applied had the highest percentage of the dose in the skin. Washing the skin with solvent 24 hours after application removed 77-92% of the applied dose. In this study, decaDBE did not easily penetrate the skin, but inferences to dermal absorption in humans based on these limited results may not be appropriate. 

Information on toxic effects of acute-duration exposure to PBBs by routes other than oral are limited to data on hepatic, renal, dermal, and ocular effects of inhalation and dermal exposure in rats or rabbits (Millischer et al. 1980 Needham et al. 1982 Norris et al. 1975a Waritz et al. 1977), but these data may not be reliable due to study limitations and possible delayed lethality. Quantitative data for inhalation and dermal absorption of PBBs are lacking. Studies of inhalation and dermal absorption following exposure to soil containing PBBs (i.e., bioavailability studies) would be useful for assessing risk at a hazardous waste... 

Absorption, Distribution, Metabolism, and Excretion. The database for inhalation and dermal absorption of silver compounds in humans consists primarily of qualitative evidence from occupational case studies. Limited quantitative information exists on the oral absorption of silver compounds in humans. Research into the quantitative absorption of various silver compounds following relevant exposure routes would be useful to better predict the potential for toxic responses to particular silver compounds in humans. 

Okrent and Xing (1993) estimated the lifetime cancer risk to a future resident at a hazardous waste disposal site after loss of institutional control. The assumed exposure pathways involve consumption of contaminated fruits and vegetables, ingestion of contaminated soil, and dermal absorption. The slope factors for each chemical that induces stochastic effects were obtained from the IRIS (1988) database and, thus, represent upper bounds (UCLs). The exposure duration was assumed to be 70 y. Based on these assumptions, the estimated lifetime cancer risk was 0.3, due almost entirely to arsenic. If the risk were reduced by a factor of 10, based on the assumption that UCLs of slope factors for chemicals that induce stochastic effects should be reduced by this amount in evaluating waste for classification as low-hazard (see Section 7.1.7.1), the estimated risk would be reduced to 0.03. Either of these results is greater than the assumed limit on acceptable risk of 10 3 (see Table 7.1). Thus, based on this analysis, the waste would be classified as high-hazard in the absence of perpetual institutional control to preclude permanent occupancy of a disposal site. 

Data regarding dermal absorption of CDDs in animals are limited. When 200 pmol 2,3,7,8-TCDD was applied to the skin of Fischer 344 rats, absorption followed first-order kinetics with an absorption rate constant of 0.005 hour"1 (Banks and Bimbaum 1991). Within 120 hours postexposure, about 0.026 g... 

TCDD (Koshakji et al. 1984). Also, limited information is available on the bioavailability from fly ash (Van den Berg et al. 1983, 1985). 2,3,7,8-TCDD can be adsorbed following dermal contact (Banks and Bimbaum 1991 Poiger and Schlatter 1980 Shu et al. 1988) however, dermal absorption of... 

As is apparent from Figure 3-6, there are minimal data on health effects following dermal absorption. In addition, there were only two studies on toxicokinetics that used the dermal exposure route. Although there are several animal studies that evaluated the health effects of DEHP through the respiratory route, these studies are also limited in scope. In each case, exposures were at very low levels and without effect. Although the exposure concentrations were relevant to human exposures through inhalation, the lack of observed effects makes it difficult to evaluate whether there are specific risks that apply to respiratory exposures. 

No data are available in animals from standard studies of acute toxicity using the inhalation or dermal routes of exposure. Therefore, an MRL value for acute inhalation exposures cannot be derived. DEHP concentrations in the atmosphere are limited by the low vapor pressure of this compound. Dermal absorption of neat DEHP is demonstrated as minimal (Deisinger et al. 1991 Melnick et al. 1987). 

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