Dermal exposure estimation

Table IX. Dermal Exposure Estimation by Patch and Tracer Techniques...

The use of percutaneous penetration data to correct dermal exposure estimates Is In its Infancy, and there are numerous aspects which must be Investigated before this becomes an accepted regulatory procedure. 

Eye and Skin Contact. Some nickel salts and aqueous solutions of these salts, eg, the sulfate and chloride, may cause a primary irritant reaction of the eye and skin. The most common effect of dermal exposure to nickel is allergic contact dermatitis. Nickel dermatitis may occur in sensitized individuals following close and prolonged contact with nickel-containing solutions or metallic objects such as jewelry, particularly pierced earrings. It is estimated that 8—15% of the female human population and 0.2—2% of the male human population is nickel-sensitized (125). 

Very few data are available on the effects of organotins in humans. Of the reported unintentional occupational exposures, none has an estimate of exposure concentration. Exposure was largely via the inhalation route, with some possibility of dermal exposure. Neurological effects were the most commonly reported, and these can persist for long periods. 

Estimates of exposure levels posing minimal risk to humans (Minimal Risk Levels or MRLs) have been made for methyl parathion. An MRL is defined as an estimate of daily human exposure to a substance that is likely to be without an appreciable risk of adverse effects (noncarcinogenic) over a specified duration of exposure. MRLs are derived when reliable and sufficient data exist to identify the target organ(s) of effect or the most sensitive health effect(s) for a specific duration within a given route of exposure. MRLs are based on noncancerous health effects only and do not consider carcinogenic effects. MRLs can be derived for acute, intermediate, and chronic duration exposures for inhalation and oral routes. Appropriate methodology does not exist to develop MRLs for dermal exposure. 

Serum endosulfan was 4 pg/L at 30 hours after an agricultural pilot was exposed dermally (and probably also by inhalation) for approximately 45 minutes in clothing that was heavily contaminated with endosulfan and methomyl (Cable and Doherty 1999) the dermal exposure level was not estimated and no other measures of tissue levels of endosulfan were obtained. A study by Kazen et al. (1974) has identified endosulfan residues on the hands of workers after relatively long periods free from exposure. Endosulfan residues were identified on the hands of one worker approximately 30 days after exposure and on the hands of one worker who had not used endosulfan during the preceding season. 

R.C. Honeycutt, The Usefulness of Farm Worker Exposure Estimates Based on Generic Data, in Dermal Exposure Related to Pesticide Use Discussion of Risk Assessment, ed. R.C. Honeycutt, G. Zweig, and N.N. Ragsdale, ACS Symposium Series 273, American Chemical Society, Washington, DC, pp. 369-375 (1985). 

Information on the excretion of americium after dermal exposure in humans or animals is extremely limited. Some qualitative information is available from an accidental exposure in which a worker received facial wounds from projectile debris and nitric acid during an explosion of a vessel containing 241 Am (McMurray 1983). The subject also inhaled 241Am released to the air as dust and nitric acid aerosols, which was evident from external chest measurements of internal radioactivity thus, excretion estimates reflect combined inhalation, dermal, and wound penetration exposures (Palmer et al. 1983). Measurements of cumulative fecal and urinary excretion of241 Am during the first years after the accident, and periodic measurements made from day 10 to 11 years post accident indicated a fecal urine excretion ratio of approximately 0.2-0.3, although the ratio was approximately 1 on day 3 post accident (Breitenstein and... 

Urinary excretion of radioactivity was measured in human volunteers during and after a 3.5-hour period of dermal exposure to 0.11 or 0.22 g 32P-labeled TOCP (Hodge and Sterner 1943). The specific activity of the test substance was not reported. Radioactivity in urine was measured with a Geiger-Muller counter, but the limits of detection were not reported. Maximum estimated excretion rates, 10 and 43 pg TOCP/hour for the respective dosage levels, were measured within 24 hours of initiation of exposure. Radioactivity was not detected 48 or 72 hours after dosing ceased. Cumulative radioactivity detected in urine accounted for 0.13% and 0.36% of the dermally applied radioactivity. 

Organophosphate Ester Hydraulic Fluids. Organophosphate ester hydraulic fluids are used in applications that require a degree of fire resistance such as in aircraft. EPA (1992b) has noted that aircraft mechanics may have dermal exposures of 1,300-3,900 mg/day and that 2,200 aircraft workers are routinely exposed to tributyl phosphate, while another 43,000 mechanics may be exposed at various times. Estimates of worker exposure in other industries were not found in the available literature. General population and military personnel exposure to organophosphate ester hydraulic fluids is likely to be much lower than exposure to mineral oil hydraulic fluids because these fluids have more specialized uses. 

Head, neck, and hand exposures were measured using methods outlined in the literature.4 Head patches were used to estimate dermal exposure to the neck and face of the worker. Handwashes were conducted using a 0.008% DSS solution and collected in 2-L Pyrex bowls. The handwash was repeated with distilled water, and the two handwash solutions were combined. The pooled handwash was then partitioned with ethyl acetate to remove the chlorpyrifos from the aqueous phase. An aliquot of the ethyl acetate was shipped to the analytical laboratory for analysis of chlorpyrifos. 

The internal dose of propoxur was measured by assessing the total amount of 2-isopropoxyphenol (IPP) excreted in the urine, collected over a period of 24 hr from the start of exposure, and described in detail in previous studies (Brouwer et al., 1993 Meuling et al., 1991). Volunteer kinetics studies revealed a one-to-one relationship of absorbed propoxur and excreted IPP on a mole basis. Based on the results by Machemer et al. (1982), a pulmonary retention of 40% was used to calculate the relative contribution of the respiratory exposure to the internal exposure. To estimate the contribution of the dermal exposure, the calculated respiratory portion was subtracted from the total amount of IPP excreted in urine. 

Krieger, R.I., Bernard, C.E., Dinoff, T.M., Fell, L., Osimitz, T. G., Ross, J.I., and Thongsinthusak, T. (2000) Biomonitoring and whole body cotton dosimetry to estimate potential human dermal exposure to semivolatile chemicals, /. Exposure Anal. Environ. Epidemiol., 10 50-57. 

The factor k (the transfer factor) was defined as a crop- and task-specific factor and is defined as the slope of the line that fits dermal exposure levels (g/hr) and corresponding levels of DFR (g/m2) on the crop (i.e., the regression coefficient of DFR). The DFR, according to the procedures described by Iwata et al. (1977), was considered to be a good estimate of source strength for re-entry exposure. 

The first pesticide exposure study was reported by Griffiths et al. (1951). Parathion was trapped on respirator filter discs during application to citrus trees. Batchelor and Walker (1954) expanded exposure monitoring to include the estimation of potential dermal exposure using pads attached to workers clothing. Durham and Wolfe (1962), in their classic review of worker exposure methodologies, also provided some experimental validation for the best available methods. 

In the early 1980s, the whole-body dosimeter (WBD) was introduced as a superior method for passive dermal dosimetry monitoring. A standard protocol was described by the World Health Organization (1982), and Abbott et al. (1987) described some additional options. Chester (1993) reported refinements that permitted exposure estimation by passive dermal dosimetry and biological monitoring simultaneously. 

Nickel is found in air, soil, water, food, and household objects ingestion or inhalation of nickel is common, as is dermal exposure. Recent estimates suggest that as much as 28,100 tons of nickel are introduced into the atmosphere each year from natural sources and as much as 99,800 tons from human activities. In the atmosphere, nickel is mostly suspended onto particulate matter. In natural waters, the dominant chemical species is Ni2+ in the form of (Ni(H20)6)2+. In alkaline soils, the major components of the soil solution are Ni2+ and Ni(OH)+ in acidic soils, the main solution species are Ni2+, NiS04, and NiHP04. 

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. 

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