Pesticide Use and Free Radicals

In recent years, there has been mounting concern over the possible effects of pesticide residues in food. The use of such substances in agriculture is both necessary and widespread. However, many of these materials have been associated with various pathophysiologic phenomena. For example, the herbicide, paraquat, exerts its toxic effects through the intracellular formation of free radicals. Fortunately though, government regulatory mechanisms serve to minimize public exposure. According to the Federal Insecticide, Fungicide, and Rodenticide Act, a pesticide is defined as "any substance or mixture of substances intended for preventing, destroying, repelling, or mitigating any insects, rodents, nematodes, fungi, or weeds, or any other forms of life declared to be pests; and any substance or mixture of substances intended for use as a plant regulator, defoliant, or desiccant" (Archibald & Winter, 1990, p. 3). The use of such agents involves both benefits and risks. For example, the pesticides increase crop yields, protect stored food, and enhance the general attractiveness of many food products. It has been estimated that, without them, 40% of the world's food supply might be in jeopardy (Archibald & Winter, 1990, p. 2). However, pesticides may also have negative effects. In general, these compounds are biologically active and can harm the environment. In addition, the presence of undesirable residues in the a

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h electron transfer from a transition metal such as iron or copper to some oxygencontaining molecule. Such reactions may occur practically anywhere in the cell. Sites of free radical generation include the mitochondria, the lysosomes, the peroxisomes, as well as the nuclear, endoplasmic reticular, and plasma membranes. The reactions may even occur within the cytosol (Machlin & Bendich, 1987, p. 441). Lastly, an additional major source of free radicals is the oxidation of oxyhemoglobin in red blood cells (Brunori & Rotilio, 1984, pp. 2223). Sequential oneelectron reductions of dioxygen (O2) produce a variety of highly reactive species. The first reduction product, the superoxide, O2, is a base in equilibrium with its conjugate acid, the hydroperoxyl radical, O2H. The pH of this equilibrium, pK = 4.8, is sufficiently close to normal physiological pH values that both molecules may be involved in superoxide ion reactions. The next reduction product, the twoelectron molecule, is the peroxide ion. This may form both hydrogen peroxide and the hydroperoxyl anion, O2H. Thirdly, the threeelectron reduction product of dioxygen exists only hypothetically. The molecule, [O23], is thought to be the precursor of oxide and
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Approximate Word count = 2370
Approximate Pages = 9 (250 words per page)

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