Biochemical mechanisms pesticides

Asztalos, B., J. Nemcsok, I. Benedeczky, R. Gabriel, A. Szabo, and OJ. Refaie. 1990. The effects of pesticides on some biochemical parameters of carp (Cyprinus carpio L). Arch. Environ. Contam. Toxicol. 19 275-283. Autor, A.P. (ed.). 1977. Biochemical Mechanisms of Paraquat Toxicity. Academic Press, New York. 240 pp. Babich, H., M.R. Palace, and A. Stern. 1993. Oxidative stress in fish cells in vitro studies. Arch. Environ. Contam. Toxicol. 24 173-178. 

Casida JE, Toia RF. Organophosphorus pesticides their target diversity and bioactivation. In Dekant W, Neumann HG, eds. Tissue Specific Toxicity Biochemical Mechanisms. London Academic Press, 1992. Coburn RF, Forman HJ. Carbon monoxide toxicity. In Fahri LE, Tenney SM, eds. Flandbook of Physiology, The Respiratory System, Section 3, Vol. IV, Bethesda, MD American Physiology Society, 1987. Ellenhorn MJ, Barceloux DG. Medical Toxicology, New York Elsevier, 1988. 

During the 1950s, an era when biochemical knowledge developed very fast, there was a very strong belief that by finding the biochemical mechanism for resistance, it should be easy to find some substance that counteracted it, for instance, inhibitors of enzymes that detoxicate the pesticide or a new pesticide that shows higher activity toward the resistant insects. 

Pesticides are subject to considerable loss by evaporation when they are thinly spread over large areas of crop exposed to moving air. In this situation they are subject also to biochemical, photochemical, and solution losses which make it difficult to assess directly evaporation under field conditions. The rate of evaporation of water is easily determined and has been the subject of much experiment. The relationship of loss of pesticide to loss of water from the same surface can be verified by laboratory experiments. Crystallization and solution in leaf substances exert some effect also. When the pesticide is distributed in the soil, evaporation of water can accelerate that of the water-soluble pesticide the mechanism lies in capillary flow of solution and not in the evaporation process itself. 

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. 

Here, too, a better knowledge of their biochemical modes of action and of pest vulnerability and defenses will be indispensible. However these goals can be fully realized only if there is greater investment in research into pesticidal mechanisms and responses in target and non-target species. 

The biochemical and physiological mechanisms may be many, but resistance is often due to an insensitive target for the pesticide or to increased detoxication. 

Pesticides can be transformed by chemical, photochemical, and biochemical means. Soil can provide the conditions or serve as the catalyst or component for chemical reactions. Chemical reactions are mediated by such soil properties as pH or catalyzed by soil minerals (20). Photolysis of a chemical can result directly from absorbing radiation or indirectly by reaction with another chemical which is activated by absorbed radiation. However, the predominant means of transformation is microbial or enzymatic. Mechanisms of these reactions have been extensively reviewed and summarized (21-23). 

Lack of information concerning the microorganisms and the mechanisms involved in enhanced EPTC degradation has seriously limited attempts to control the rapid breakdown of this herbicide, and other carbamothioate pesticides, in soil. This study was initiated to 1) evaluate enhanced EPTC degradation in field and laboratory soils, 2) isolate soil microorganism(s) active in degrading EPTC and 3) determine the biochemical pathway(s) of EPTC degradation by the isolated microbes. 

The exact mechanisms for microbial adaptation to the pesticide molecule in soils that develop enhanced degradation capacity are not completely understood. These processes could be viewed from the ecological and population aspects, from their biochemical and enzymatic reactions, or from the genetic aspects, in which extrachromosomal elements may be involved as part of the process. 

Pesticides are determined to have a common mechanism of toxicity if they aci the same way in the body that is, if scientifically reliable data dcmon.strate that upon exposure to these chemicals, the same toxic effect occurs in or at the same organ or tissue by essentially the same. sequence of major biochemical events. The OPs were the first common mechanism of toxicity group identified by EPA and are the first pesticides to undergo a full cumulative risk assessment. More than 30 OPs are included in the CMG. However, not all are included in the cumulative assessment group (CAG). 

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