Pesticides biochemical basis

Parathion and Paraoxon. Again, this represents a reaction (the sulfur oxidation of a thiophosphate pesticide) that is familiar to most in the pesticide area. Unlike heptachlor epoxide, paraoxon is not a stable compound and its actual presence in a poisoned animal was very difficult to demonstrate. The oxons of other organo-phosphorothioates are not so elusive. In any event, the paraoxon metabolite is an excellent example of where an understanding of metabolic processes and their potential toxicological significance alerted scientists to the likelihood that such a metabolite existed. Many years of work with similar compounds had established that the insecticidal thiophosphates required oxidation to the P=0 form in order to inhibit the neurotrasmitter acetylcholinesterase, the biochemical basis of their toxic action. Paraoxon was eventually isolated in vivo and now consideration of the oxon is a vital part of the overall risk assessment of this group of pesticides. 

Such information has led to explosive growth in the understanding of biochemical processes. Knowledge of metabolism, biosynthetic processes, neurochemistry, regulatory mechanisms, and many other aspects of plant, animal and insect biochemistry has provided a basis on which the mode of action of a pesticide may often be more clearly understood. The exploitation of biological information can lead to the synthesis of a new molecule designed to act at a particular site or block a key step in a biochemical process. 

These developments indicate potential new modes of selective insecticidal action. Through a better understanding of the physiological processes, the basis of screening can be broadened and the increased knowledge of the diverse biochemical pathways suggests new approaches to the design of pesticides. 

Biochemical pesticides include, but are not limited to, products such as semiochemicals (e.g., insect pheromones), hormones (e.g., insect juvenile growth hormones), natural plant and insect regulators, and enzymes. When necessary the Agency will evaluate products on an individual basis to determine whether they are biochemical or conventional chemical pesticide. ... 

Brassinosteroids, therefore, would qualify for classification as biochemical pesticides. Once they are classified as biochemical pesticides, the data requirements for U.S. registration would be significantly reduced (because of a tier approach), especially in the areas of toxicology, ecology and wildlife, and environmental fate. Because of their low use volume, brassinosteroids are unlikely to leave any residues in crops, and they would qualify for exemption from the requirement of a tolerance. If that were the case, what applicants seeking U.S. registrations need to do is to develop data on product chemistry and acute toxicology, as well as use profiles for their products, which will be dealt with on a case-by-case basis. 

The Clean Water Act lays the basis for technology based effluent standards of conventional pollutants such as Biochemical Oxygen Demand (BOD), Total Suspended Solids (TSS), fecal coliform, oil and grease, pH, toxic pollutants, and non-conventional pollutants such as active pesticides, ingredients used in the pesticide manufacturing industry, etc. 

The problem of eliminating side-effects on nontarget organisms is most studied in insecticide research. This is partly because the recognition of specific biochemical and behavioural characteristics of insects has created a good theoretical basis for research, and partly because, of all pesticides, insecticides represent the greatest... 

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