Total dermal exposure

The calculation of potential total dermal exposure of mixer-loaders and re-entry workers using dosimetry data and calculation of the internal dose using biological monitoring data is complex but will be discussed briefly. 

Total dermal exposure (TDE) was calculated using the following steps ... 

Add to this value the micrograms chlorpyrifos found in the handwash and head patches (corrected for surface area of the head and neck). This sum in terms of ug/kg body weight per day represents the total dermal exposure (TDE). 

Table 4 Regression Analyses of All Total Dermal Exposure Data (mg/hr) as Dependent Variable to Average DFR, Number of Harvested Flowers, and Re-entry Time...

Davis et al. (1983) reported that dermal exposure to diazinon from spray applications of the compound for home and garden applications ranged from 5,700 to 29,000 pg/hour depending on the type of sprayer used. The mean respiratory exposures ranging from 1.9 to 7.4 pg/hour, were negligible compared to the dermal exposures. In addition, these authors reported that dermal exposure of the hands, which accounted for 85% or more of the total dermal exposure, could be easily reduced by the use of protective gloves. 

The dermal exposure patches were made of 9-ply gauze (2,4,5-T study) or denim (2,4-D study) and were attached with safety pins to workers clothing by research team members wearing clean gloves. Following the spray activities, the patches were placed in individual specimen bottles and transported to the laboratory for analysis. In the 2,4,5-T study, all six patches from each individual were pooled before analyses were made in the 2,4-D studies the patches were kept separate and analyzed individually. Using a photograph of the worker in his spray attire and the amounts of pesticide found on the patches, we estimated total dermal exposure for each worker (Durham and Wolfe, 1962). 

Patches to collect measurements of dermal exposure were attached to clothing on the chest, back, thighs and forearms of each individual. To calculate total dermal exposure, the concentration of 2,4,5-T detected on the patch area was multiplied by the total skin area exposed (Lavy, 1978). 

Respiratory exposure was assessed with personnel-type air samplers (see Table 5-2). Total dermal exposure to applicators to chlordane was 2.5 pg/kg/hour. The most exposed body regions in descending order were hands, forearms, head, lower legs, thighs, back trunk, front trunk, upper arms, and back neck. Approximately 25% of the clordane on the exterior surface of clothing was likely to penetrate through the fabric. Respiratory exposure was 0.04 pg/kg/hour. 

Dermal eoqposure to residents to DDVP oouH not be assessed however, it was noted that the environmental eaqxjsure pads received 0.31910.183 pg/on /hr during the application u)d the two hrs post-initiation. This r esents 63.9% of the total dermal exposure of the applicators. 

Total dermal exposure to applicators of Chemical Y was determined by field tests to be 0.2 mg/hour. Using the CCF the exposure of applicators using Chemical X versus Y can be determined 0.2 mg/hour X 0.13 0.026 mg/hour. 

Studies showing the portion of dermal exposure that has been attributed to the hands are summarized In Table III. Regardless of the isethod used to measure hand exposure these studies show that the hands contribute from 272 to 99% of the total dermal exposure. In mlxer/loader situations where the worker Is more likely to contact the concentrate, the majority of dermal exposure is to the hands regardless of whether extra protective gloves were worn over the cotton gloves or a closed mixing system was used. 

Wojeck (13) used eight outside patches and the palms and back of cotton gloves to estimate total dermal exposure to mixer/loaders or alrblast applicators of ethlon. Mlxer/loaders received 76% of the total dermal exposure to the hands and applicators received 42% of the total dermal exposure to the hands. If the original patch method of Durham and Wolfe ( ), which did not include a hand exposure estimate is used to recalculate the data, the total dermal estimate, was 10 times lower than the total body method used by Wojeck. This emphasizes the Importance of using hand exposures to more accurately estimate total exposure. 

In another study using the same method, Wojeck (14) measured exposure of mlxer/loaders and alrblast applicators using arsenic spray. Hand exposure accounted for 52% and 41% of total dermal exposure for mlxer/loaders and applicators respectively. 

Table III. Hand Exposure Expressed as a Percentage of Total Dermal Exposure... 

Maddy (16) monitored dermal and Inhalation exposures for mlxer/loaders, flaggers and pilots associated with the aerial application of mevlnphos, using Che methods described In Peoples (15). In this study the mlxer/loaders operating closed transfer systems wore gloves but others associated with the spray operation did not. The mlxer/loaders received 74% of their total dermal exposure on Che hands, flaggers received 42% and pilots received 27%. Pilots received a considerably lower proportion of Che total exposure Co the hands Chan In the study by Peoples (15). 

Everhart (17) monitored 8 mlxer/loaders who each prepared one tankful of benomyl for aerial application. Five gauze pads and cotton gloves were used to measure exposure. Most workers wore additional protective gloves over the cotton gloves. Regardless of this additional precaution 96% of the total dermal exposure was found on Che cotton gloves. In almost all other cases Che forearm patches had the highest levels of contamination. 

Although various patch techniques were used as well as different methods of estimating hand exposure in these studies, they all emphasize the Importance of including an estimate of hand exposure in calculating the total dermal exposure. The available data do not clearly indicate which procedure for estimation of hand exposure is the most accurate. Since it has been suggested that cotton gloves overestimate hand exposure it would be prudent from the point of view of health protection to use this method until better methods are designed. 

Unfortunately the Ideal situation does not exist and there are many difficulties which must be overcome before accurate risk assessments can be conducted. For pesticide applicators, the dermal route has been shown to be the most Important one. However, the methods used to measure the amount of pesticide landing on the skin are not very reliable and many studies conducted In the past did not try to estimate hand exposure. This omission Is a serious one because it has been shown that a very large percentage of the total dermal exposure Is to the hands. New methods using fluorescent tracer techniques are promising and will undoubtedly lead to more quantitative estimates of contact exposure. 

The California Department of Food and Agriculture (CDFA) has attempted to estimate pesticide exposure of body areas protected by clothing. This report summarizes experimental studies which attempt to estimate total dermal exposure and the different amounts of this exposure which occur on various parts of the body. 

Tables I, II, and III summarize the average percentage of total dermal exposure found on various regions by individual chemical and job activity, respectively. The hands are not considered to be a protected area, as such, even though waterproof gloves were usually worn. Table IV summarizes the amounts of pesticide that were estimated to have reached the skin.

The results presented in the Tables show that estimated exposure to protected body areas represented, on the average, 23.3 percent of the total dermal exposure. Statistical analysis utilizing one-way analysis of variance was performed to determine whether the average percentage of total dermal exposure found on the unprotected areas... 

Questions arise as to the necessity of monitoring protected areas if only 23.3 percent of the total dermal exposure occurs in these areas. A qualitative study of worker exposure using fluorescent tracers led to the conclusion that "results depend critically on knowing where to place the pads" (11). This study also demonstrated that the principal exposure was to the face, hands, and neck. 

Table II. Relative Contributions to Total Dermal Exposure of Body Areas to Pesticides as Studied by the California Department of Food and Agriculture...

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