Pesticide regulations for agriculture: Chemically flawed regulatory practice

Abstract

Two categories of pesticide soil models now exist. Government regulatory agencies use pesticide fate and transport hydrology models, including versions of PRZM.gw. They have good descriptions of pesticide transport by water flow. Their descriptions of chemical mechanisms are unrealistic, having been postulated using the universally accepted but incorrect pesticide soil science. The objective of this work is to report experimental tests of a pesticide soil model in use by regulatory agencies and to suggest possible improvements. Tests with experimentally based data explain why PRZM.gw predictions can be wrong by orders of magnitude. Predictive spreadsheet models are the other category. They are experimentally based, with chemical stoichiometry applied to integral kinetic rate laws for sorption, desorption, intra-particle diffusion, and chemical reactions. They do not account for pesticide transport through soils. Each category of models therefore lacks what the other could provide. They need to be either harmonized or replaced. Some preliminary tests indicate that an experimental mismatch between the categories of models will have to be resolved. Reports of pesticides in the environment and the medical problems that overlap geographically indicate that government regulatory practice needs to account for chemical kinetics and mechanisms. Questions about possible cause and effect links could then be investigated.

The Physical Chemistry of Pesticides in Soil and Water

“…Stoichiometry was ignored in this chapter. 3 Contrary to experimental evidence [17], the authors assumed that the kinetic rate coefficients were constants. 4…”

“…The above equation incorrectly neglects one of the two reactants, empty sorption sites, b [1,17]. In addition to its other problems [1,17], the octanol-water coefficient k OH also does not account for empty sorption sites.…”

“…In addition to its other problems [1,17], the octanol-water coefficient k OH also does not account for empty sorption sites. This chapter not only ignores chemical kinetics and mechanisms, it also ignores first year chemistry descriptions of equilibria.…”

“…Spot checks are the only practical way of testing what is still being done. Because it should have been the most authoritative choice, the published proceedings of the 2014 IUPAC-AgroChem Symposium were selected as a case study [17,18].…”

“…Chemical kinetics order is defined for individual processes or reactions, not groups of them lumped together as these authors have done [17]. 2 For each pesticide soil process, all of the reactants and products have to be accounted for.…”