DEVELOPMENT OF A STANDARD SOIL-TO-SKIN ADHERENCE PROBABILITY DENSITY-FUNCTION FOR USE IN MONTE-CARLO ANALYSES OF DERMAL EXPOSURE

It has recently been suggested that ''standard'' data distributions fo r key exposure variables should be developed wherever appropriate for use in probabilistic or ''Monte Carlo'' exposure analyses. Soil-on-ski n adherence estimates represent an ideal candidate for development of a standard data distribution: There are several readily available stud ies which offer a consistent pattern reported results, and more import antly, soil adherence to skin is likely to vary little from site-to-si te. In this paper, we thoroughly review each of the published soil adh erence studies with respect to study design, sampling, and analytical methods, and level of confidence in the reported results. Based on the se studies, probability density functions (PDF) of soil adherence valu es were examined for different age groups and different sampling techn iques. The soil adherence PDF developed from adult data was found to r esemble closely the soil adherence PDF based on child data in terms of both central tendency (mean = 0.49 and 0.63 mg-soil/cm2-skin, respect ively) and 95th percentile values (1.6 and 2.4 mg-soil/cm2-skin, respe ctively). Accordingly, a single, ''standard'' PDF is presented based o n all data collected for all age groups. This standard PDF is lognorma lly distributed; the arithmetic mean and standard deviation are 0.52 /- 0.9 mg-soil/cm2-skin. Since our review of the literature indicates that soil adherence under environmental conditions will be minimally i nfluenced by age, sex, soil type, or particle size, this PDF should be considered applicable to all settings. The 50th and 95th percentile v alues of the standard PDF (0.25 and 1.7 mg-soil/cm2-skin, respectively ) are very similar to recent U.S. EPA estimates of ''average'' and ''u pper-bound'' soil adherence (0.2 and 1.0 mg-soil/cm2-skin, respectivel y).