Document LgOxoB3jaRYmKD5G5DNN45VpX

Ann. wxup. Hyv.. Vol. 37. No. 6. PP,687-706. 1993. Prinled in S r u t Britain. 000344878/93%.00+0.00 Per moo Press Ltd British Oecupaliond#ygiene Society. DERMAL EXPOSURE ASSESSMENT TECHNIQUES R.A. FENSKE Department of Environmental Health, SC-34, School of Public Health and Community Medicine, University of Washington, Seattle, WA 98195, U.S.A. (Received 2 March 1993 and injinal form 16 June 1993) Abstract-Exposure of the skin to chemical substances can contribute significantly to total dose in many workplace situations, and its relative importance will increase when airborne occupational exposure limits are reduced, unless steps to reduce skin exposure are undertaken simultaneously. Its assessmentemploys personal sampling techniques to measure skin loading rates, and combines these measurements with models of percutaneous absorption to estimate absorbed dose. Knowledge of dermal exposure pathways is in many cases fundamental to hazard evaluation and control. When the skin is the primary contributor to absorbed dose, dermal exposure measurements and biological monitoring play complementary roles in defining occupational exposures. Exposure normally occurs by one of three pathways: (i)immersion (direct contact with a liquid or solid chemicalsubstance); (ii) deposition of aerosol or uptake of vapour through the skin; or (iii)surface contact (residue transfer from contaminated surfaces). Sampling methods fall into three categories: surrogate skin; chemical removal; and fluorescent tracers. Surface sampling represents a supplementary approach, providing an estimate of dermal exposure potential. Surrogate skin techniques involve placing a chemical collection medium on the skin. Whole-body garment samplers do not require assumptions relating to distribution, an inherent limitation of patch sampling. The validity of these techniques rests on the ability of the sampling medium to capture and retain chemicals in a manner similar to skin. Remoual techniques include skin washing and wiping, but these measure only what can be removed from the skin, not exposure: laboratory removal efficiency studies are required for proper interpretation of data. fluorescent tracer techniques exploit the visual properties of fluorescent compounds, and combined with video imaging make quantification of dermal exposure patterns possible, but the need to introduce a chemical substance (tracer) into production processes represents an important limitation of this approach. Su$ace sampling techniques provide a measure of workplace chemical contamination. Wipe sampling has been used extensively, but is susceptible to high variability. Surface sampling requires definition of dermal transfer coefficients for specific work activities. A preliminary dermal exposure sampling strategy which addresses such issues as sampling method, representativeness and sample duration is proposed. Despite the limitations of current assessmenttechniques, it appears feasibleto consider developingdennaloccupational exposure limits (DOELs)for selected workplaces and chemical agents. Initial development of DOELs would be most practical wheredermal exposure is from surface contact primarily, and where the work closely follows a routine. Improvement in the techniques of dermal exposure assessment is an important goal for occupational hygiene research, and is likely to lead to better health for worker populations. INTRODUCTION SKIN exposure to chemical substances can contribute significantly to total absorbed or systemic dose in many workplace situations, as well as result in local manifestationsof illness (e.g. dermatitis). Recent studies have indicated that for particular work tasks it is a primary contributor to absorbed dose for such compounds as chlorophenols (KAUPPINEaNnd LINDROOS1,985; FENSKE et af., 1987), polychlorinated biphenyls (LEES et af.,1987), polycyclic aromatic hydrocarbons (JONGENEELEN et al., 1988; VAN ROO~eJt af., 1992),glycol ethers (JOHANSON1,988),chlorpyrifos (FENSKEand ELKNER, 1990), acrylamide (CUMMINS et af.,1992),cyclophosamide (SESSINKet af.,1992) and 4,4'-methylene dianiline (GROTH, 1992). The relative importance of the dermal exposure route will increase when airborne occupational exposure limits are reduced, 687 688 R. A. FENSKE unless steps to reduce skin exposure are undertaken simultaneously (FENSKE et al., 1989b). Despite the recognized importance of dermal exposure for many chemical substances, relatively little research has focusedon developing tools to measure dermal exposure directly. Indeed the most recent edition of Patty's Industrial Hygiene and Toxicology omits the topic entirely from its chapter on industrial hygiene sampling and analysis (SOULE, 1991), and a recent scientific conference on occupational exposure assessment and hazard control did not include discussion of dermal exposure (RAPPAPORT and SMITH, 1991). The U.S. Environmental Protection Agency has published a comprehensive discussion of skin absorption and risk assessment for nonoccupational exposures, but makes only passing mention of exposure measurement techniques (U.S. EPA, 1992a). Professional organizations and governmentalagencies in the United States have generally addressed the issue by recommending a policy of prevention; i.e. qualitative recognition of dermal exposure potential leading to control strategies to eliminate exposure (ACGIH, 1991; NIOSH, 1991). Where quantitative estimates are deemed necessary, biological monitoring has been proposed to estimate the relative contribution of the dermal route. Only in the area of occupational pesticide exposure, where dermal exposure has been considered the primary contributor to dose for 30 years, has direct measurement of such exposure been required ( U S EPA, 1987). As a result, the most substantial efforts to develop standard methods and new approaches to its assessment have occurred in this field. Skin exposure is an interactive process between a source and a worker (Fig. I), and is defined as the mass of chemical reaching the body barrier (skin) and available for rnabsorption per unit time.This source-receptorrelationship is characterizedby analysis SOURCE I exposwcpathway analysis I percutaneous absorption analysis phamucokinetic analysis BIOLOGICAL DETERMINANTS FIG. 1. Dermal exposure assessment components. of exposure p toxicological occurs. The at body barrier particularly ir barrier for che be measured i i such concent pharmacokin, role analog01 assessment in monitoring tc dose. Methods I and the coml addressed in therefore dis pathways, ev; dermal expo dermal occul Current ( measure ski] monitoring c and policies (ACGIH, 19 grounds (Ta Rationale Hazard eval Hazard cont Dermal is pt of exposure Biological n impractical First. IT evaluation. and extent behaviour. (FENSKeEt al., many chemical measure dermal in1 Hygiene and 'esampling and tional exposure xmal exposure In Agency has .sment for non~2 measurement mental agencies iding a policy of ading to control ere quantitative ,sedto estimate tional pesticide ributor to dose .S. EPA, 1987). .iods and new .er (Fig. 1 ), and d available for zed by analysis Dermal exposure assessment techniques 689 of exposure pathways. As with the respiratory and oral routes skin exposure is of toxicological significance systemically only if absorption across the body barrier occurs. The absorbed dose, or internal dose, is defined as the mass passing through the body barrier into systemic circulation. Knowledge of the absorption process is particularly important for the dermal route, since the skin generally provides a good barrier for chemical substances. The concentration of a chemical or its metabolites can be measured in blood, urine, breath and other fluids and tissues, but the relationship of such concentrations to internal dose requires a thorough analysis of human pharmacokinetics. Thus, dermal exposure measurements can be viewed as playing a role analogous to that of air sampling within the context of occupational exposure assessment in that direct measurements of exposure are complemented by biological monitoring to fully define sources and exposure pathways, and to estimate absorbed dose. Methods for measuring skin exposure were reviewed recently (MCARTHUR1,992a), and the complexities of percutaneous absorption of chemical substances have been addressed in detail elsewhere (FISEROVA-BERGEROVA, 1990, 1993). This paper will therefore discuss the need to assess dermal exposures, define dermal exposure prthways, evaluate the relevance of current sampling techniques within the context of a dermal exposure assessment strategy, and consider the feasibility of establishing dermal occupational exposure limits for the skin. RATIONALE FOR D E R M A L E X P O S U R E ASSESSMENT Current occupational hygiene literature suggests that there is little or no need to measure skin exposure directly, since air sampling supplemented with biological monitoring can provide sufficient information for risk estimates and standard setting, and policies to prohibit exposure of the skin will provide adequate worker protection (ACGIH, 1991; NIOSH, 1991).This prevailing attitude can be challenged on several grounds (Table 1). T A ~ LI .ERATIONALE FOR DERMAL EXPOSURE ASSESSMENT Rationale Dermal exposure measurement goal Accuracy Alternative or required complementary approaches Hazard evaluation Hazard control Dermal is primary route of exposure Gioiogical monitoring impractical Define exposure pathways Relative Test effectiveness of controls Relative Estimate dose from dermal route Estimate dose from dermal route Absolute Absolute 0 Visual observation 0 Assume controls effective 0 Biological monitoring 0 Biological monitoring 0 Prohibit dermal exposure First, measurements of dermal exposure can play an important role in hazard evaluation, helping in characterizing exposure pathways, in quantifying the magnitude and extent of skin contamination, and in evaluating variability in sources and worker behaviour. In some workplaces the potential may appear obvious, and visual 690 R. A. FENSKE observation<can provide a sufficientbasis for gross categorization of workers, as in the case of auto body workers (DANIELL et al., 1992).In other cases dermal exposure is less predictable (e.g. episodic contact with contaminated equipment), and measurements may be required to identify sources and exposure pathways. Second, the efficiency of control strategieg designed to eliminate dermal exposure should be tested under realistic workplace conditions. In particular, chemical protective clothing (CPC)cannot be assumed to provide full protection from chemical substances (PERKINS,1987; FENSKE, 1988a; LANDER et al., 1992; ZELLERS and SULEWSKI, 1992; METHNER and FENSKE, submitted). While laboratory testing can indicate the barrier properties inherent in CPC material, efficacy is also a function of the quality of worker training, hygienic behaviour and material degradation. In such cases, direct measurement of dermal exposure is often the simplest and most costeffective approach, although biological monitoring may provide equivalent documentation of efficacy. Measurements conducted for hazard evaluation and control need not be accurate in the sense that a measured value represents total true dermal exposure. It is sufficient that they have relative validity, so that measurements taken for different workers or at different times can be compared quantitatively. This distinction is important, since the absolute accuracy of most current measurement techniques has yet to be demonstrated. The same argument can often be made for biomarkers of exposure, for example a decrease in the urinary excretion of a chemical substance following control implementation can be considered a measure of efficacy, although the relationship between internal dose and measured biological concentration may be uncertain. A third reason for assessing dermal exposure arises when the skin has been identified as the major contributor ( >50%) to dose during normal working conditions. Under these circumstances an occupational exposure limit based exclusively on air concentration measurements, even when adjusted with biological monitoring data, would be of questionable validity. The purpose of such measurements is dose estimation, requiring both accurate exposure data and adequate knowledge of percutaneous absorption. Ideally, dermal exposure measurements, air sampling and biological monitoring can be conducted as complementary efforts to estimate dose and health risk when the dermal route predominates. A final and obvious rationale for dermal exposure assessment is the absence of appropriate biological monitoring procedures. For many workplace chemical substances there are: (i) no major determinants available in an accessible biological medium; (ii) inadequate human pharmacokinetic data; or (iii) obstacles associated with worksite sampling (e.g.lack of worker co-operation, complex sampling schedule, high cost of sample analysis). In such situations, if dermal exposure is likely to contribute significantly to dose, direct measurements are required to ensure complete assessment of occupational health risk. EXPOSURE PATHWAYS The link between a chemical hazard source and a human receptor (worker) will be referred to here as an exposure pathway. Dermal exposure normally occurs by one of three pathways: immersion, deposition, or surface contact. The term 'exposure' has been defined in a variety of ways in the field of environmental and occupational hygiene. h and define which ma incorpora expressed Derm; skin and ;1 concent ra commonl: Since skir subdivide, the sum o operation where SL s This qua loading u removal t be based techniquc sampling contam i n significan exposure character exposure at the ski Immel phase chc solvent, a chemical by use c monitori 1992a). vapours 1978; Jo interior subsequt substanc colorime selected Depu producec incident; foliage). Dermal exposure assessment techniques 691 workers, as in the a1exposure is less ad measurements dermal exposure ticular, chemical ion from chemical '2; ZELLERSand dory testing can also a function of qadation. In such st and most costiivalent documen- hygiene. Most commonly exposure is viewed in the context of respiratory exposure, and defined as environmental concentration (e.g. pg m-') (CHECKOWAY et al., 1989), which may be expressed as a rate (pg m - 3 h-'). This definition can be refined to incorporate respiratory volume rate (m' h - ') to produce personal exposure values expressed as mass per unit time (pg h-I). Dermal exposure can be defined similarly, with the amount of material reaching the skin and available for absorption referred to as skin loading (e.g. pg cm-*) rather than concentration. Skin loading rate (pg cm-' h-') has the same units as flux, the term commonly employed to describe steady state movement of chemicals through the skin. Since skin loading is likely to vary across anatomical regions, the body is normally subdivided for sampling purposes (e.g. hands, forearms), and thus dermal exposure is the sum of exposure to these anatomical regions. Dermal exposure can thus be defined operationally as the product of skin loading rate and exposed skin area: d not be accurate Dermal exposure (pg h-')=C(SLR, x SA,)+. . .(SLR, x SA,), (1) ure. It is sufficient rent workers or at portant, since the et to be demonasure, for example bllowing control 3 the relationship be uncertain. ne skin has been normal working sure limit based 2d with biological >uchmeasurements quate knowledge of .air sampling and 1 estimate dose and where SLR =skin loading rate for each region (pg h-') SA =exposed skin area for each region (cm2). This qliantitative expression requires two qualifications: (i) measurement of skin loading will not reflect losses which occur subsequent to sampling; e.g. evaporation or removal by hygienic behaviour such as handwashing. Ideally dermal exposure would be based on a measurement of the net skin loading rate, but current sampling techniques do not quantify such losses from the skin. An analogous concern in air sampling is that air sampling measurements do not reflect the fact that some inhaled contaminant may be exhaled rather than retained; and (ii)dermal exposures can vary significantly over time and are often the result of discrete events; as with respiratory exposure, sampling which integrates exposure over extended periods cannot characterize variation with time. This is an important consideration for dermal 1 exposure, since skin loading will influence dermal absorption rates; the concentration 1 at the skin surface is the driving force of skin penetration (TREGEAR, 1966). Immersionoccurs when a worker's skin comes into contact with a liquid, solid or gas phase chemical substance. The most common example of this pathway is of hands in . t is the absence of xkplace chemical xessible biological bstacles associated sampling schedule, posure is likely to to ensure complete solvent, as when dipping, or furniture stripping. In these cases exposure is a function of chemical concentration, exposed skin area and exposure duration; it may be mitigated by use of chemical protective clothing, and is normally estimated by biological monitoring or by model rather than measured directly (BERODeEt a!., 1985;U.S. EPA, I992a). Several investigators have demonstrated that dermal exposure to ambient vapours can significantly contribute to dose (PIOTROWSKI, 1967; FLEK and SEDIVEC, 1978; JOHANSOanNd BOMAN, 1991). A special case of immersion occurs when the interior of gloves or other CPC becomes contaminated and these garments are subsequently worn; skin is then both occluded and in contact with a chemical substance continuously, even during work tasks with no exposure potential. The use of colorimetric indicators inside gloves can provide a signal of dermal contamination for 'tor (worker)will be .Ily occurs by one of term `exposure' has 11 and occupational selected compounds (KLINGNER, 1992). Deposition results when an aerosol or vapour impacts the skin. Aerosols may be produced as part of the work activity (spray painting, pesticide application) or may be incidental to it (emissions from a nearby process, pesticide residues dislodged from foliage).Deposition exposure is the product of skin loading rate and exposed skin area. 2: P .) ig 692 R. A. FENSKE COHEN and POPENDORF (1989) explored the feasibility of using charcoal patches to measure deposition of volatile compounds, but this approach remains experimental. Surface conlacr exposure occurs when skin touches a contaminated surface so that chemical residue transfer occurs, for example during equipment maintenance. Exposure again is the product of skin loading rate and exposed skin area, and skin loading rate is a functionof surface contamination level,contact frequency or duration, and residue transferability. Surface-to-skin transfer is a complex process involving such diverse factors as contact pressure and motion, affinity of a chemical substance for the stratum corneum, regional differences in skin composition and condition, work practices and hygienic behaviour. Surface contact clearly represents the primary exposure pathways in many worksites, including manual work in agriculture (POPENDORF and LEFFINGWE1L9L82,),transformer maintenance (LEES et al., 1987)and aircraft manufacture (GROTH, 1992). It should be noted that skin exposure by any of these pathways may also contribute to a worker's exposure by mouth (ULENBELT et al., 1990).Chemical residues on hands are frequently transferred to the eyes, nose and mouth through normal facial contact, and may also contaminate food and tobacco products. Contaminated clothing can also serve as a major source of hand exposure, despite proper use of chemical-resistant gloves (FENSKE et al., 1990). Residues on skin and clothing have also been documented as sources of `para-occupational exposure' (exposure of a worker's family members) (GRANDJEAN and BACH, 1986; KNISHKOWanYd BAKER, 1986).Thus, dermal exposure, even to chemicals not considered skin penetrants, may be an important exposure pathway in some circumstances. SAMPLING TECHNIQUES Skin exposure sampling techniques fall into three categories: surrogate skin; chemical removal; and fluorescent tracers. Surfacesampling can be considered a fourth and indirect method, since it provides an estimate of dermal exposure potential. Selection of appropriate sampling techniques should be based on knowledge of dermal exposure pathways. Surrogate skin techniques These methods involve placing a chemical collection medium against the skin and subsequently analysing it for chemical content. Two general approaches have been used: patch samplers covering small skin surface areas, and garment samplers covering entire anatomical regions. Patch samplers arose initially in the context of hazard evaluation for acute intoxications among users of organophosphorus insecticides (DURHAM and WOLFE, 1962). Patches provided a first approximation of health risk, as well as demonstrating the predominant role of dermal exposure under these conditions. The technique has since become recognized as a standard quantitative exposure method for pesticides (WHO, 1986; U.S. EPA, 1987), and its use has been extended to assessment of such occupational hazards as polycyclic aromatic hydrocarbons and dichlorobenzidene (JONGENEELEN et al., 1988; LONDON et al., 1989). Its validity as a means of assessing exposure rests on one of two critical assumptions: ( 1 ) uniform exposure, i.e. the deposition rate on the patch is representative ( the patch has bc body. These a accuracy of ex (FRANKLIN et L Patches are calculated by t anatomical reg samplers for t example, two sampled surfac characterize a representative differentwork can produce rn estimates derit The normal application b: problems sugg dermal exposi TAI - Bot Chi Thi -For *C: If these li cost-effective MACHADNO exposure by pesticide ap (submitted) exposure sut video imagir penetration : al., 1982; NI Limitatic anatomical frequently tc in harvestin; BROUWEerR to assess pe :harcoal patches to nains experimental. ,ated surface so that nent maintenance. ikin area, and skin quency or duration, ocess involving such a1 substance for the d condition, work esents the primary ork in agriculture LEES et a/., 1987)and may also contribute 11 residues on hands ,rmal facial contact, ed clothing can also i chemical-resistant o been documented i's family members) 's,dernnal exposure, mport#antexposure les: surrogate skin; IC considered a fourth exposure potential. .nowledge of dermal against the skin and proaches have been .nt samplers covering valuation for acute URHAIA and WOLFE, ell as demonstrating ,. The technique has iethod for pesticides 3 assessment of such 3 dichlorobenzidene one of two critical .e on the patch is Dermal exposure assessment techniques 693 represenlative of deposition over that part of the body; or (2)worst-case exposure, i.e. the patch has been located at the point of highest exposure potential for that part of the body. These assumptions have not been investigated systematically, so that the accuracy of exposure estimates derived from this technique is open to question (FRANKLeWt al., 1981; FENSKE, 1990). Patches are essentially spot or grab samples of the skin, whereby dermal exposure is calculated by extrapolating the patch loading level to the surface area of an entire anatomical region. Table 2 indicates the percent of the skin covered by typical 25 cm2 samplers for three anatomical regions. In the case of the chest and stomach, for example, two patch samplers represent less than 1% of the skin surface, a ratio of sampled surface area to total surface area analogous to air sampling for 4 min to characterize an 8 h exposure. The likelihood that such a limited sample will be representative of true exposure would appear low. Furthermore, exposure patterns for different work activities can differ systematically, and patch samplers placed at one site can produce misleading exposure estimates. Figure 2 illustrates differences in exposure estimates derived from wearing a head patch during pesticide mixing and application. The normal patch location (front) overestimated the average exposure during application by 35%, but underestimated exposure during mixing by 75%. These problems suggest that patch sampling inherently cannot provide accurate estimates of dermal exposures. TABLE 2. BODY SURFACE AREA REPRESENTED BY DERMAL PATCH SAMPLERS AS PER CENT SURFACE AREA AND EQUIVALENT PORTION OF AN 8 h AIR SAMPLE* Body region Patch surface area Portion of 8 h air sample Chest and stomach Thighs Forearms 0.13% 1.4% 4.3% 4 min 1 min 21 min *Calculations from FENSKE(1990). If these limitations are borne in mind, patch sampling can serve as a simple and cost-effectivemethod for hazard evaluation and control through comparative studies. MACHADONETOet al. (1992), for example, demonstrated a significant reduction in exposure by increasing the distance between workers and spray nozzles during pesticide applications in staked tomato crops. Similarly, METHNERand FENSKE (submitted) reported that unidirectional ventilation in greenhouses reduced dermal exposure substantially, and confirmed patch sampling data with fluorescent tracervideo imaging analysis. Numerous investigators have quantified protective clothing penetration by placing patch samplers inside and outside of the fabric barrier (GOLDet a/., 1982; NIGG e f al., 1986, 1992; KEEBLE et al., 1988; FENSKE et al., 1990). Limitations inherent in patch sampling can be overcome by sampling entire ailatomical regions with garments. Absorbent gloves (e.g. cotton) have been used frequently to estimate hand exposure during contact with equipment or materials, and in harvesting of crops treated with pesticides (DAVIS et al., 1983; FENSKEet al., 1989a; BROUWER et al., 1992).Whole-body garment samplers have been used most frequently to assess pesticide exposure (BONSALL1,985; ABBOTTet al., 1987), and have been 694 R. A. FENSKE 1 Front Patch <ISide Patch I 0 Applicator Mixer WORKER ACTIVITY FIG. 2.Systematic differences in head exposure estimates for pesticide mixers and applicators due to patch location (mean+standard deviation). One hundred per cent is the average value of front and side patches (from FENSKE, 1990). proposed recently as a standard method for measuring the exposure of users (CHESTER, 1992),and worker exposure to antifungal products during commercial wood treatment (TESCHKE et ai., 1992). A recent study aimed at estimating children's exposure to pesticides indoors asked subjects to wear whole-body garments while doing an exercise routine on a treated carpet (Ross et al., 1990). The major assumption underlying all surrogate skin techniques is that the collection medium captures and retains chemicals in a manner similar to that of skin, but none of the garment samplers in common use has been systematically tested for retention efficiency. Concerns have been raised regarding potential overestimation of exposure, since sampling media may be selected primarily for their absorbent properties. DAVIS et ai. (1983) found that cotton gloves collected more azinphosmethyl residues than did handwashing, but the removal efficiency of the handwash technique was not known. FENSKeEt ai. (1989) found that differences between glove and handwash measurements of captan residues decreased with increasing sample time. Thus, the accuracy of glove and other garment samplers remains an open question. Garment sampling has several advantages: distributional assumptions are not required, a standard sampling approach can be applied to virtually all body regions (e.g. hand, feet, arms, legs), and the sampling of work activities with different skin exposure patterns is comparable. Several disadvantages can also be noted: putting garments on and taking them off can be cumbersome, extraction requires large volumes of solvents, and garments are susceptible to breakthrough and may require changing during the workshift. A major obstacle to its widespread use is the lack of standard garments for sampling. In studies to date garments have been selected for convenience rather than according to scientific criteria, and garment characteristics have not been well described. For example, two recent studies state only brand name and fabric content (B.C. RESEARCH, 1989; Ross et ai., 1990), whereas at least fibre content, construction, finish, weight and thickness should be specified. Ideally garments empl and retain the Removal technl Chemicals ( ant mixes or v exposure, whilc skin surfaces. that they are o whereas skin-u and thus inclu, demonstrated I spray delivery : thus cannot pr Measureme skin at the time employing the: implicit assumf a standard la1 techniques. Ev; for the pesticidc exposure, and decreased with collected by chc require appro1 assurance. Fluorescent trtr, Dermal ex[ deposition of fl hydrocarbons I allowing identil VO-DIHN, 1987 allows rapid ic designed to intl The use of measurements I ol., 1986a.b). 1 longwave U.V. fluorescence to relationship be deposited on sh resulted in a se analysis has bee METHNER and (FENSKE et 01.. children to pes1 cators due to patch mt and side patches users (CHESTER, wood treatment 7's exposure to 3ing an exercise ies is that the to that of skin. cally tested for erestimation of their absorbent more azinphosthe handwash between glove reasing sample mains an open .ptions are not 4 body regions h different skin noted: putting requires large Id may require \e is the lack of ;en selected for characteristics ily brand name Lsat least fibre xilied. Ideally Dermal exposure assessment techniques 695 garments employed as dermal samplers would be pre-tested for their ability to absorb and retain the particular chemical under study. Rrmoual techniques Chemicals deposited on skin can be removed by washing or wiping. Water-surfact- ant mixes or water-alcohol wash solutions are generally used only to assess hand exposure, while wiping techniques can in theory be applied to larger and more diverse skin surfaces. Handwash sampling procedures can normally be standardized to ensure that they are operator-independent, so that studies can be compared (DAVIS, 1980), whereas skin-wiping relies on procedures which are inherently operator-dependent, and thus include an unknown component of variability. KEENANand COLE (1982) demonstrated the feasibility of washing skin contaminated with coal liquids with a spray delivery system, but the technique is designed to sample only 5 cmz of skin, and thus cannot provide an integrated measure of dermal exposure. Measurements of chemical removal represent only what can be removed from the skin at the time of sampling rather than the actual skin loading. Yet most investigations employing these techniques have reported measured values as `exposure', on an implicit assumption that removal was 100%.FENSKE and Lu (1993)recently proposed a standard laboratory procedure for assessing removal efficiency of handwash techniques. Evaluation of several handwash techniques indicated a removal efficiency for the pesticide chlorpyrifos of less than 50% when skin was washed immediately after exposure, and less that 25% 1 h post-exposure. Furthermore, removal efficiency decreased with decreased skin loading. These findings suggest that exposure data collected by chemical removal techniques are likely to be difficult to interpret, and will require appropriate laboratory removal efficiency studies as a part of quality assurance. Fluorescent tracer techniques Dermal exposure can be quantified directly and non-invasively by measuring deposition of fluorescent materials. The natural fluorescence of polycyclic aromatic hydrocarbons has been exploited by use of a small scanning device (luminoscope), allowing identification of skin contamination patterns (VO-DINH and GAMMAGE, 1981; VO-DIHN, 1987). The luminoscope can provide spot samples of contamination and allows rapid identification of skin surfaces requiring decontamination, but is not designed to integrate exposure over large surface areas. The use of fluorescent compounds (Fig. 3) can be coupled with video imaging measurements to produce exposure estimates over virtually the entire body (FENSKE er nl., 1986a,b). This requires pre- and post-exposure images of skin surfaces under longwave U.V.illumination, development of a standard curve relating dermal fluorescence to skin-deposited tracer, and chemical residue sampling to quantify the relationship between the tracer and the chemical substance of interest as they are deposited on skin. Advances in hardware and exposure quantification procedures have resulted in a second generation imaging system (FENSKE er al., submitted). Imaging analysis has been applied primarily to pesticide mixers and applicators (FENSK1E9.88b; METHNERand FENSKE, submitted) as well as to workers handling treated lumber (FENSKE er nl., 1987), and has been extended recently to estimating the exposure of children to pesticides (BLACK. 1993). 696 R. A. FENSKE Ideally this method can provide improved accuracy in dermal exposure assessment, since it measures actual skin loading levels, requires no distributional assumptions, and can identify hitherto unrecognized exposure pathways. In practice, however, it has several important limitations: (i) use of a tracer requires the introduction of a foreign substance into the production system. In most agricultural settings this has not posed a problem, since the tracer compounds used to date do not appear to be phytotoxic or otherwise incompatible with pesticide use, but for many industrial processes addition of a foreign chemical substance could not be tolerated without extensivepre-testing; (ii) the relative transfer of the tracer and chemical substance of interest must be demonstrated during field investigations. This need for ancillary studies involving chemical extraction and analysis to some extent undermines the primary advantages of video imaging; i.e. samples are collected and analysed rapidly, and cannot degrade; (iii) additional quality assurance steps may be required during field studies, including range-finding and the evaluation of potential tracer degradation due to sunlight; and (iv) when protective clothing is worn, separate studies may be required to determine the relative fabric penetration of the tracer and the chemical substance of interest. In studies of protective clothing performance patch sampling is likely to be more sensitive than video imaging, although not necessarily more accurate (METHNER and FENSKE, submitted; FENSKE, 1993). Qualitative use of fluorescent tracers can indicate dermal exposure patterns and identify differential exposure potential among worker groups, and is also valuable for worker education and training (BENTLEeYt al., 1989).Quantitative studies are likely to be most successfulwhen the amount of tracer deposited on or transferred to the skin is predictable as with controlled spraying or routine surface contact activities rather than spills and splashes. Recent applications and innovations with this technique are promising. ARCHIBALD (1993) has reported on its use for assessing post-application exposure assessment in Canadian greenhouses, and BIERMAetNal. (1992)have initiated laboratory studies with a modified imaging system. ROFF (1992)has proposed a major advance in the illumination system used for quantifying fluorescence.His dodecahedral lighting system illuminates all skin surfaces evenly, reducing the number of correction factors which must be employed in the quantification procedures. Surface sampling techniques Contaminated surfaces have long been recognized as an occupational health hazard. Surface sampling has been addressed most systematically in the field of radioactive contaminants (DUNSTER19,62; IAEA, 1970). The U.S. Occupational Safety and Health Administration has published a standard wipe sampling procedure for workplace surfaces (OSHA, 1990),and several investigators have tested or modified it (CHAVALITNITKUL and LEVIN,1984; LICHTENWALNER, 1992; FENSKEet al., 1991; MCARTHUR1,992b). These studies indicate that wiping a discrete area is critical to reducing sampling variability, and that physical surface characteristics, contaminant surfzce loading, sampling material and wipe sampling procedures all influence the accuracy and precision of measurements. There is a clear need to develop a surface sampling technique which employs standard materials and procedures, samples a defined surface area, and is operatorindependent; Le. pressure is not produced by hand motion. The goal of such a technique is to provide a reproducible measure of what ROYSTERand FISH (1967)called FIG.3. Flu01 right ear an posure assessment, I assumptions, and e, however, it has uction of a foreign his has not posed a J be phytotoxic or processes addition ive pre-testing; (ii) interest must be studies involving iary advantages of nnot degrade; (iii) studies, including !eto sunlight; and to determine the ce of interest. In be more sensitive VER and FENSKE. .ure patterns and also valuable for Jdies are likely to red to the skin is vities rather than s technique are post-application 12)have initiated jroposed a major His dodecahedral i e r of correction pational health in the field of i.Occupational ipling procedure sted or modified KE et d.,1991; rea is critical to :s, contaminant 111 influence the which employs 1.nd is operatorgoal of such a `SH ( 1967)called FIG. 3. Fluorescent tracer deposition on the face following airblast pesticide application. Exposure to the right ear and side of face is evident. Dark bands indicate areas covered by half-mask respirator straps. Dermal exposure assessment techniques 699 "removabie residues"; which will be referred to here as `transferable'residues. Thus, it is not necessary or even desirable to remove 10Oo/o of surface residues, but to measure those residues which are iikely to be tranferred to human skin. This sampling objective is exemplified by the development of the `dislodgeable residue' concept as applied to fieldworkers exposed to pesticides; Le. the hazardous component of residues found on foliar surfaces is considered to be only that which can be dislodged from the leaf surface due to worker contact, rather than total extractable foliar residue (IWATA er al., 1977). Several sampling instruments incorporating standard features have been developed recently for estimating surface pesticide residues in homes. Hsuer al. (1990)have used a polyurethane foam roll attached to a roller which delivers a known pressure to a measured surface independent of the operator. VACCARO (1990) developed a `sled' consisting of a fixed weight on top of sampling material; the sled is dragged across a measured surface at a fixed rate. Ross ef al. (1991) placed sampling material of known dimensions on a surface, covered it with a plastic sheet, and then rolled a weighted roller across the surface according to a standard protocol. Preliminary studies indicate that these techniques remove surface contaminants with comparable reproducibility, but that such measurement$ may not be representative of actual surface-to-skin transfer (Lu and FENSKE, submitted). Surface sampling, like area sampling of air concentrations, can be considered a first approximation of personal exposure. If surface sampling and dermal exposure sampling are conducted simultaneoiusly, a dermal transfer coefficient (DTE) can be calculated for a specific work activity, and dermal exposure can be estimated subsequently from measurements of transferable surface residues. DTEs have been calculated for a number of pesticide exposure scenarios in agriculture (Nrcc et af., 1984; ZWIG et af., 1985; KRIEGERet a!., 1992). The general form of the transfer coefficient is as follows: 'Dermal transfer coefficient (cm' h - Dermal exposure (pg h-') =Transferable residue (pg cm-') . (2) The transfer coefficient is interpretable as a rate of surface contact frequency. A high degree of variability in DTEs across workers can be anticipated in some industries owing to differences in work practices (KRIEGER et al., 1992; GROTH, 1992). DERMAL EXPOSURE SAMPLING STRATEGY Sampling strategy design should be based on a recognition that exposures are likely to vary widely over time and between workers (RAPPAPORT, 1992).Dermal exposure depends both on process and on behaviour so that not only can source strength be highly variable, but work practices and hygienic behaviour represent major components of variability. It is therefore to be expected that both within-person and between-person variability of dermal exposures will be greater than that of corresponding respiratory exposures. A preliminary sampling strategy for dermal exposure has been proposed by BROUWER and VAN HEMMEN(1992), and is outlined in Table 3. Several issues can be highlighted. First, sampling must be representative; that is, all skin surfaces with potential forexposure need to be identified and monitored. In practice the exposed skin surfaces may be obvious and quite limited (e.g. hands). Under many circumstances, 700 R . A. FENSKE ...... b. ...... 0.. however, de unpredictab sample durc, techniques r over a work washing or employed c substantiall: regions wit' samplers, sc evaluation concentratic Third, e. hygiene ma exposure, b predict, as clothing des a workshift (MARQUAR Assessm production across an antisapstair substantial (TESCHKE e TAW Sampling ga Gloves Shirt Hood Socks Pants *From TES( tAssumes 8 HORSTMA.K at the outs primarily b: for workers of these WOI tracers was at particuli selected to The sa1 Dermal exposure assessment techniques 70I however, dermal exposure can extend over substantial portions of the body, and is unpredictable for example as the result of accidents or of unusual conditions. Second, sample duration should be tailored to the sampling technique selected. Removal techniques require sampling immediately after exposure events, but frequent sampling over a workshift may alter the barrier properties of the skin (e.g. use of alcohols for washing or wiping may drive compounds into the skin). When garment samplers are employed care must be taken to avoid saturation. Exposure intensity can vary substantially over regions of the body, and double-layered samplers may be needed for regions with high breakthrough potential. Losses may also occur from garment samplers, so that samplers may have to be changed periodically. Fluorescent tracer evaluation requires range-finding studies to determine the appropriate tracer concentration for specific exposure scenarios. Third, exposure mitigation by the use of chemical protective clothing or by personal hygiene may confound exposure measurements. CPC is designed to prevent skin exposure, but under actual conditions of use its performance is extremely difficult to predict, as it depends on worker behaviour patterns as well as on the integrity of clothing design and of materials. Additionally, normal washing during or at the end of a workshift can be expected to remove some fraction of a chemical deposited on skin (MARQUART et ul., 1992). Assessment of occupational exposure to antifungal agents during commercial wood production serves to illustrate how a dermal sampling strategy might be implemented across an industry. Exposure assessment guidelines to support registration of antisapstain agents were prepared recently in British Columbia, and included a substantial discussion of the statistical basis for the proposed sampling strategy (TESCHKE et al.. 1992). Based on previous work in this industry (KLEINMAN and TABLE 4. DERMAL EXPOSURE SAMPLING STRATEGY FOR COMMERCIAL WOOD TREATMENT* Sampling garment Body region Number of changes (times per day) Sampling timet (h) Gloves Shirt Hood Socks Pants Hands Upper torso;'arms Head Feet Lower torso!legs 4 (at breaksllunch) 2 (at lunch) 2 (at lunch) 1 I 2 4 4 8 8 *From TESCHKetEul. (1992). tAssumes 8 h workshift. HORSTMAN, 1984; FENSKE et al., 1987)and an occupational hygiene survey conducted at the outset of the project, it was concluded that dermal exposure would occur primarily by one of two pathways: deposition for handlers of formulated products and for workers in the vicinity of dipping and spraying operations; surface contact for many of these workers and for all other workers at the facility. Qualitative use of fluorescent tracers was recommended to characterize exposed populations and exposure pathways at particular worksites, and surrogate skin techniques (garment samplers) were selected to measure dermal exposure. The sampling guidelines proposed (Table 4) were: (i) employ standardized 102 R. A. FENSKE sampling garments; i.e. uniform fabric, construction, weight, thickness; (ii) sampling garments should include gloves, shirt, hood, pants and socks to measure exposure to all regions of the body; (iii) wear sampling garments beneath protective clothing or normal work clothing; clothing worn normally by workers should not otherwise be Acknoivledyemerirs including K. Black was presented in International Sciei Brussels, Belgium. altered; (iv) sample over the entire workshift, including clean-up of equipment and .y. materials at the end of the shift; and (v) change sampling garments at regular intervals (e.g.glovesfour times per shift),and more frequently if there is evidence of saturation or ABBOTTI..M.. Bo E if the compound under study is volatile. Repeat sampling of individual workers was also included in the strategy. This study design could be expected to produce exposure herbicide appl ACGlH (1991) D American Cor data sufficient to compare work activities and worksites, and suitable for use in risk ARCHIBALBD..A assessment models. chrysanthernu Program. Gub B.C.RESEARCH ( I Research Cor DERMAL OCCUPATIONAL EXPOSURE LIMITS WP88;6). V a Despite the limitations of current assessment techniques, it appears feasible to BENTLEYR,. K . . chlorophenol consider developing dermal occupational exposure limits (DOEL) for selected BERODEM, ..DHI workplaces and chemical agents. Sampling procedures designed to ensure compliance with standards should be relatively simple and inexpensive, as is the case with personal I;lfh 55, 33 I BIERMAEN. .P. f an image ana air sampling. Surface sampling fulfils these criteria and in theory is the most practical First Interna technique available for workplace monitoring for dermal exposure. Initial development of DOELs based on surface sampling would be most feasible where: (i) dermal BLACK. K . G. ( 1 Ph.D. Dissei Jersey. exposure is from surface contact primarily; and (ii) work activities closely follow a BONSALL. J . ( I $ routine. Under these circumstances daily exposures are likely to vary over a manageable range, and exposure can be estimated on the basis of surface residue Pesticide C .\ BROUWERR... % of greenholl measurements and dermal transfer coefficients. In fact agricultural worker re-entry BROUWER.D. r intervals represent occupational standards derived in large part from measurements of transferable residues; i.e. residue levels on foliar surfaces (KRIEGER et al., 1992, assessment. Conference. CHALK ( 1989)4 POPENDORF, 1992; U.S. EPA, 1992b). Similarly, recent efforts to measure exposure to Aspects i)1 .- 4,4'-methylene dianiline (MDA)during composite material handling have focused on defining target levels for surface contamination (CHALK, 1989; GROTH, 1992). 60-63. CHAV.4LITlilTlh surface con Development of DOELs for surface contact exposure scenarios will require: (i) CHECKOWAY. reproducible and representative methods for measuring surface residues and daily dermal exposure; (ii) establishment of dermal transfer coefficients across a range of Epidmtirdoc CHESTER. G . I and re-entr surface residue levels and work activities; and (iii) validation of dermal dose estimates pesticides. by biological monitoring. Risk assessments incorporating these data would also require knowledge of exposure frequency (days/year)and duration (years),percutan- COHENB.. M. ..hi.t i d . H CLMMISSK.. . eous absorption rates for absorbed dose estimation, and dose-response relationships sewer grot for specific health endpoints. Substantial work is needed to establish a full understanding of dermal exposure DANIELWL.. . to solcent D ~ V IJS. .E. I pathways. The contribution of dermal exposure to dose in many occupational settings 33-50. is still unclear, and studies designed to address this question under realistic exposure conditions pose unique challenges. Yet if one considers the status of occupational DAVIS. J. E.. and comp 631 638. exposure assessment of airborne contaminants 20-25 years ago, and in particular the DLSSTEK. H. quality of air sampling techniques and sampling strategies, it would appear that with sufficient effort the dermal route of exposure can be characterized quantitatively, H/rh PI1.r. DURHAMW. Hetdrh 01 leading to a reduction in occupational exposures and better health for worker populations. FESSKE. R . dsrrndl e \ thickness; (ii) sampling ' measureexposure to all protective clothing or hould not otherwise be n-up of equipment and cnts at regular intervals .idence of saturation or individual workers was ed to produce exposure {uitable for use in risk A ITS it appears feasible to 'DOEL) for selected to ensure compliance the case with personal is the most practical sure. Initial developible where: (i) dermal ities closely follow a ely to vary over a is of surface residue ural worker re-entry om measurements of RIEGER et Uf., 1992, measure exposure to ,ling have focused on SROTH, 1992). rios will require: (i) * residues and daily ts across a range of mnal dose estimates ;e data would also In (years), percutan.pome relationships of dermal exposure xupational settings :r realistic exposure US of occupational nd in particular the .Id appear that with zed quantitatively, health for worker Dermal exposure assessment techniques 703 Acknoi~/edqernenrs-I offer sprcial thanks to students and staff who have contributed to progress in this field. including K. Black, S. Birnbaum, K. Elkner, W. Gibb. C . Lee, C. Lu. M. Methner and S. Wong. This paper was presented in preliminary form at the International Occupational Hygiene Association First International Scientific Conference. Workshop on Occupational Skin Exposure to Chemical Substances. 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(1985) The relationship between dermal pesticide exposure by fruit harvesters and dislodgeable foliar residues. J. Enuiron. Sci. HIth Part B 20, 27-59. THE subject three separ: industrial h: impact of a When I 25% of wh; Thus, obso We nee discover ne past and pr for Legion radon. Toc proved cor that radon Anothc providing contamin: trillion. Sc significant Then t active in c United S industrial know no While educatior *Paper