Pesticides current modeling approaches

One of the main objectives of the EC project APECOP ° was to develop process descriptions for pesticide volatilization from plants and to include them in the current PEC models (predicting environmental concentrations of pesticides), PEARL, PELMO, and MACRO. As a screening-level approach for estimating the initial volatilization rate after plant application, a correlation between physicochemical pesticide properties and measured volatilization fluxes was used. For the prediction of cumulative losses from plant surfaces, a similar estimation method was developed by Smit. Despite intense research in recent years, including the development of numerous laboratory and field methods to measure volatilization rates," " knowledge of rate-determining processes is currently not sufficient for developing a reliable, physically-based model approach to predict fluxes of pesticide volatilization from plant surfaces. 

Although more predictive approaches may be possible in the future, with the ethical considerations of utilizing humans in studies with pesticides, currently the laboratory rat appears to be a suitable model. Dermal absorption studies with the rat allow the calculation of a penetration rate and hence, assist in the estimation of a potential body burden in man. Indeed, the extrapolation of a dermal penetration rate in the rat to man may represent a worst case approximation. Studies with one pesticide, malathion, in the rat and man have revealed the absorption/ penetration rate in the rat to be approximately 3-fold higher than man ( ). 

Another major difference between the current approach and the previous approach for evaluating the adverse effects of pesticide exposure involves the way in which the toxicity data are interpreted. In the current system, the carcinogenicity data from the chronic rodent studies are extrapolated using mathematical models which provide a numerical estimate of the upper bound of the cancer risk, and these numbers (Q values) are then used for a variety of regulatory purposes. In essence, this approach substitutes mathematical guidelines for the scientific judgement that was the key element in the earlier approach. 

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