Pesticide model

Cory-Slechta DA.Thiruchelvam M, BarlowBK, Richfield EK. Developmental pesticide models of the Parkinson disease phenotype. Environ Health Perspect 2005 113(9) 1263 70. 

The basic principles of modeling the physical, chemical and biological processes that determine pesticide fate in unsaturated soil are reviewed. The mathematical approaches taken to integrate diffusion, convection, sorption, degradation and volatilization are presented. Deterministic and stochastic models formulated to describe these processes in a soil-water pesticide system are contrasted and evaluated. The use of pesticide models for research or management purposes dictates the degree of resolution with thich these processes are modeled. 

There are at least two major criteria that can be used to classify models (1). One criterion is the manner in which basic processes are considered, i.e., whether they are assumed to be deterministic or stochastic. All pesticide models currently in the scientific literature or in use are deterministic. That is, they presume that the soil-water-pesticide system operates such that the occurrence of a given set of events leads to a uniquely-definable outcome. Such models can only simulate the system s response to a single set of assumed conditions, and... 

A number of experimental studies have established that both microbial and chemical degradation can be approximately described by first-order kinetics (24). Most pesticide models employ such an approach. As with linear sorption, this relatively naive representation of a fundamentally more complicated process is a simplifying assumption to make mathematical solutions possible and data requirements reasonable. Implicit in the assumption is the belief that the accuracy of simulation of pesticide fate is more dependent upon other factors than a very precise representation of the degradation process. These factors include spatial and temporal variability of the degradation process itself as affected by water, temperature, substrate, and pH, and variability in the transport of pesticide through the soil profile. There is little information to substantiate this assumption, although some field experiments on water and solute movement (discussed below) indicate it to be reasonable at this point in model development. 

The formulation of a pesticide model upon the basis of Equation 2-4 has also been cast into doubt by field studies that demonstrate that many field soils do not meet the underlying assumptions used in developing those equations. The assumption that a single pore size distribution prevails in a field soil, through which water and solutes move uniformly over the entire... 

The above issues raise serious questions about the manner in which current pesticide models should be used, the reliability of their predictions, and the direction of future pesticide modeling efforts. 

Several points are clear. First, no pesticide model exists that has been proven to estimate consistently and accurately the spatial and temporal distribution of pesticide concentrations in the unsaturated zone. This is true regardless of the resolution... 

The important assumptions for the pesticide model are instantaneous, linear, reversible adsorption described by an adsorption partition coefficient, K, and first-order decay described by an overall decay rate, k. Parameters for the pesticide model include universal soil loss equation parameters (if erosion loss is to be modeled), pesticide application information (rate, date, and method of application), K, k, and a dispersion coefficient. 

Kalisiak et al. (2011) introduced amidine oximes (40 Figure 72.30) as non-quatemary reactivators. Prepared compounds were tested on human AChE or BCJiE inhibited by nerve agent- and OP-pesticide model compounds. Novel molecules responded better to non-quatemary oxime MINA, but were worse reactivators than pralidoxime. Kalisiak et al. (2011) prepared cyclic amidine oximes (41 Figure 72.30) in a study meant to be an improvement of the previous investigation. The prepared com-poimds were tested on human AChE- or BChE-inhibited by nerve agent- and OP-pesticide model compoimds. Some compoimds performed better than MINA or pralidoxime, but bisquatemary standards were not compared in this research. Ongoing research efforts are focused... 

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