Chapter 10 - Metabolism of Organophosphorus and Carbamate Pesticides

Abstract

The chapter provides an overview of the characteristics of enzymes-catalyzing pesticide metabolism, and common metabolic pathways of organophosphorus (OP) and carbamate (CM) pesticides. Also, it presents a recent trend of using human tissue for the in vitro study of pesticide metabolism, which may provide more relevant data to human health. The study of xenobiotic metabolism focuses on the recognition of enzymes involved and identification of metabolites generated as well as the understanding of the effects of xenobiotics on the metabolic enzymes. Several families of metabolic enzymes, often with wide arrays of substrate specificity, are involved in OP and CM pesticide metabolism. These metabolic enzymes are often divided into two distinct groups, referred to as phase I and phase II enzymes. Phase I enzymes introduce a polar reactive group onto the molecule, making it more water soluble while also increasing the possibility for further metabolism by phase II enzymes. More often than not, these metabolic processes are detoxication reactions. However, there are some cases in which metabolism through either phase I or phase II can make the chemical more reactive than the parent compound. This is particularly true in the case of OP compounds, in which the conversion of a P=S moiety to a P=O group can result in increasing toxicity substantially. Usually, however, metabolic events that increase the water solubility of a chemical cause significant reductions in its biological half-life by making it more readily excreted.