Dermal pesticide residue data

Different methods of human exposure assessment vary with respect to the input data or information required and the degree of uncertainty associated with resulting estimates. Eor example, the film-thickness approach to dermal exposure assessment is a screening-level methodology that assumes a uniform layer of material (e.g., a liquid consumer product) is on the skin, and that a portion of the material in this layer is absorbed, per the dermal absorption characteristics of the chemical. In contrast, dermal exposure assessment and percutaneous absorption methods can include metrics that account for time-dependent exposure and absorption processes. Eor example, in the case of secondary dermal contact with chemicals on surfaces (e.g., transfer of pesticide residues from... 

There are no data on intermediate-duration inhalation or dermal exposures in either humans or animals. Data on intermediate inhalation and dermal exposures would be useful since the inhalation of vapors or direct contact with residual heptachlor from residential pesticide application or at NPL sites may be potential routes of exposure for the general population. 

Toxicity can occur secondary to exposure to treated fields since many of these compounds may be easily absorbed across the skin. The potential for dermal absorption is compound dependent and varies from 2-70% of the applied dose. These compounds may also be metabolized while being absorbed across the skin, and the environmental conditions during exposure (temperature, relative humidity) drastically modify absorption. Similarly, solvent effects and coapplication of other pesticides may modify the amount absorbed, making risk assessment from single-chemical data difficult. This is a primary reason that occupational exposure, and not food residues, should be the primary focus of pesticide toxicology. 

In contrast to these data, a reasonable literature base exists on the disposition of topically applied fenthion, a systemic organophosphate pesticide. Topical treatment of dairy cows with fenthion at clinically effective doses resulted in detectable but nonviolative residues in milk (24) or body fat (25). In this latter study, 90% of the residues detectable in the fat of treated cattle was parent compound. When the metabolic profile of fenthion was compared after dermal and intramuscular administration, very few differences were noted except for the time course of radiolabel clearance from the animals (26). It was not possible in these studies to study the mechanism of dermal fenthion metabolism more precisely. 

Further, different routes of exposure such as dermal, or inhalation exposure are of much more importance than exposure via the oral route. Thus, the old concept of minimal toxicity data for pesticides which do not leave residues in food is being abandoned. 

Reentry intervals are now established on the basis of (1) data on dermal absorption or dermal dose response (2) inhalation, dermal, and oral acute toxicity studies in animal models (3) foliar and soil residue dissipation data and, (4) available human exposure data. CDFA recommends several sources as useful guides for determining residues of pesticides on soil and leaf surfaces (dislodgeable residue) and conducting field reentry studies involving human volunteers (1-5). Human exposure studies may not be required if adequate animal data from (1) through (3) above are... 

Then, from the worker exposure data, an average and a maximum exposure level for each type of work activity involved with pesticide use is taken into consideration. The number of workers in each job category, the total yearly body dose (which may be derived from number of hours/days/months exposure in performing the job), and the total dermal absorption is all taken into consideration. Residue levels (including degradation products) found in treated crops or a particular product are used to assess consumer risk. 

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