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|This third case
study involves a person's occupation as the major source of exposure. The primary exposure
pathway is through dermal contact during reentry to a treated field. The basic algorithm
for calculation of dermal dose from this exposure pathway is: [dermal reentry exposure]
= [dislodgeable foliar residues] x [hourly dermal transfer rate] x [exposure
The term dislodgeable foliar residues (DFR) is defined as the amount of (pesticide) residues that can be removed from (both sides of) treated foliage surfaces using aqueous surfactant. The residues on the leaf discs punched in the field are to be dislodged in the lab through some standardized agitation force exerting on the solution for a fixed time period before extraction.
Here dermal transfer rate (TR) is referred to simply as the ratio (or sometimes some other relation, such as linear regression) of hourly dermal exposure (i.e., residues on the skin or clothing) typically inm g/hr to DFR in m g/cm2. Both of these variables should be measured more or less concurrently but separately. When multiplied with a proper dermal TR, whose value is either learned through other studies or based on some professional judgement, the DFR under study may be readily converted to hourly dermal exposure of workers reentering treated areas. U.S. EPA (2000a) has published a list of the dermal coefficients (TR) for a great variety of reentry activities.
The calculations of the doses, if any significant, from drinking water, ambient air, dietary intake, and hand-to-mouth from eating fruits (e.g., strawberries) at the field, are essentially the same as those discussed in the first case.