Pesticide measuring dermal absorption

Shah PV, Fisher HL, Sumler MR, et al. 1989. Dermal absorption and pharmacokinetics of pesticides in rats. ACS Symposium Series No. 382(Biological Monitoring for Pesticide Exposure Measurement, Estimation, and Risk Reduction) 169-187. 

Currently, for pesticide registration, there is an increasing consideration by regulatory jurisdictions of in vitro data as an alternative to in vivo dermal absorption data. At present, based on the OECD inventory and provided that levels of the pesticide remaining in the skin are included as absorbed, the results from in vitro methods seem to adequately reflect those from in vivo experiments, so supporting their use as a replacement test to measure percutaneous absorption (OECD, 2000 van de Sandt et al., 2004). This calculation, i.e. the inclusion of the amount... 

An important aspect of a refined occupational or residential exposnre assessment (Tier 2 assessment) is inclusion of a study to measure the dermal absorption of the pesticide which enables an estimate of systemic exposnre (dose) to be derived from the measnrement of dermal deposition. This step is necessary to allow comparison with the toxicity data which are generated primarily following oral exposure to the test animals. 

Navidi, W.C. and Bunge, A.L. (2002). Uncertainty in measurements of dermal absorption of pesticides. Risk Analysis, 22, 1175-1182. 

Two general types of methods are available for estimating human exposure to pesticides. First, direct entrapment methods involve the use of some mechanism to entrap the toxic material as it comes in contact with the person during an exposure period. The amount of entrapped toxicant, as determined by chemical analysis, is then a direct measure of the particular exposure under study. Further calculations using the kinetics of dermal absorption for the compound and formulation under study are required to arrive at the actual ateorbed dose. For the oral and inhalation routes, exposure and absorbed dose are more closely equivalent than for the dermal route. However, for precise data, absorption must be taken into account for these routes, also. Second, indirect methods are based on measurement of some effect of the compound on the exposed individual (such as blood... 

Hand rinses will not account for dermal absorption and may thus lead to lower exposure values. On the other hand, glove monitors which have not become moisture-saturated may keep dermal absorption at a minimum by acting as a physical barrier but may still overestimate exposure. Further research is needed to determine which of these monitoring techniques are capable of measuring actual dermal exposure to pesticides. 

Since air was an extremely minor pathway to absorbed dose and since there was a very poor correlation between the amount of pesticide on the patches and the amount of pesticide in the urine, we have chosen in our last phenoxy study to analyze only urine samples since they provide a measurement of the absorbed dose whether its entry into the body is via oral ingestion, inhalation, or dermal absorption. 

Although the extent of absorption was not measured, the above evidence suggests that absorption in humans occurs rapidly following dermal exposure to commercial pesticide formulations of methyl parathion. 

Occupational disease, caused by skin contact with toxic substances, represents a major health problem In the United States (1). Dermal exposure of agricultural workers to pesticide agents, of course. Is a particularly pertinent example of this problem. Prediction of the detrimental toxic effects of hazardous chemical exposure Is difficult, however, because of the complexity of the percutaneous absorption process in man and a lack of any consistently Identifiable relatlonshlp(s) between transport rate and chemical properties. In addition, the very diverse approaches, which have been used to measure skin penetration, further complicate the situation since the extrapolation of results to man In his workplace may Involve questionable, non-valldated assumptions. Our specific aim Is to predict accurately the toxicokinetics of occupationally-encountered molecules (e.g., pesticides) absorbed across human skin In vivo. We present... 

Research on the parameters and kinetics of pesticide absorption from human dermal contact, on the measurement of absorbed residue... 

---