Dermal exposure variances

In order to evaluate "within-worker" variances of dermal exposure and its distribution over the body, whole-body monitoring during three applications and concomitant re-entry was performed for high-volume (HV) applicators (n = 4) and harvesters of carnations (n = 6). 

The variances of potential dermal exposure are presented in Table 1. Very large "within-worker" variances of potential exposure of the hands resulted in insignificant differences between workers. For harvesters, a similar result was obtained for potential exposure of the body parts. For both applicators and harvesters, significant "between-worker" differences of total potential exposure were observed. 

The design of a study by Davies et al. (1982) for mixers and applicators was similar to that of Nigg and Stamper (1983). "Between-days" variances of exposure were not given. Mean urinary metabolite concentrations were used to show reduction of internal exposure by protective clothing. The design of the study by van Rooij et al. (1993) was similar to our study (i.e., "within-worker" comparisons of internal exposure). Because no potential dermal exposure was assessed in this study, "within-worker" variances of potential exposure are not known. 

As an example, consider the data on day-to-day and interindividual variability of fruit growers respiratory and dermal exposure to captan shown in Table 7.3 (de Cock et al., 1998a). The ratio of the 97.5th percentile to the 2.5th percentile of the exposure distribution R95) is usually larger for the intraindividual or day-to-day variability, when compared to the interindividual variability. The variance ratio, k, can be calculated from the Rgs values, since the standard deviation of each exposure distribution is equal to In R95/3.92, and the square of the standard deviation gives the variance. For the respiratory exposure, this results in a variance ratio k of 32.8, whereas for dermal exposure of the wrist the variance ratio is considerably lower, approximately 3.0. What are the implications of these variance ratios for the number of measurements per study subject For a bias of less than 10 % (or /P > 0.90), the number of repeated measurements per subject... 

Worker Exposure Variability. One of the objectives of this study was to examine the variability of dermal exposure rates and the effects, if any, of external factors on these rates. To determine the significance of individually consistent behavioral patterns having a possible influence on individual exposures, an analysis of variance (ANOVA) was performed on the data in Table VI and the results are shown in Table VII. It is apparent from this analysis that the day... 

Table VII. Analysis of Variance of Dermal Exposure Incorporating "Day" and "Individual"as Categorical Predictors...

The feasibility of employing fluorescent tracers and video imaging analysis to quantify dermal exposure to pesticide applicators has been demonstrated under realistic field conditions. Six workers loaded a tracer with the organophosphate pesticide, diazinon, into air blast sprayers, and conducted normal dormant spraying in pear orchards. They were examined prior to and immediately after the application. UV-A illumination produced fluorescence on the skin surface, and the pattern of exposure was digitized with a video imaging system. Quantifiable levels of tracer were detected beneath cotton coveralls on five workers. The distribution of exposure over the body surface varied widely due to differences in protective clothing use, work practices and environmental conditions. This assessment method produced exposure values at variance with those calculated by the traditional patch technique. 

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... 

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