Pesticides

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Pesticides are a heterogeneous group of chemicals that, by definition, are produced and used to exert biological activity. There are thousands of naturally occurring pesticides in all kinds of plants and, currently, some 500 different synthetic molecules in more than 5000 formulations. As diverse as their chemistry are their respective biological targets and modes of action. They are used as herbicides, fungicides, insecticides, acaricides, rodenticides, and microbicides. Against this background, it is impossible to give a summary evaluation of liver or kidney effects of these substances in farm workers or residents (see Chapters 13 and 16).

Most insecticides act primarily as neurotoxins, with much lower effective doses in insects than in mammals. They elicit symptoms in the central and peripheral nervous system much earlier than in any other organ system. This explains why, except in cases of deliberate poisoning, as in suicide, manifest liver or kidney damage due to insecticide use hardly ever occurs in persons who handle them professionally. One exception to this statement may be lead arsenate, which was used as an insecticide in vineyards in the past and allegedly caused liver cirrhosis and liver cancer in wine growers. Such cases have been acknowledged as an occupational disease in Germany; however, some doubted the relevance of arsenic as the major culprit. Elevated liver enzyme activities in professional pesticide sprayers have occasionally been reported, whereas others did not confirm these findings (19-25).

Some fungicides act via inhibition of the P450 enzyme family and can thus interfere with xenobiotic metabolism in mammals. Although liver damage has been found after administration of fungicides in experimental animals, liver and kidney toxicity of most of these substances is insignificant in humans under normal circumstances. Notable exceptions from this rule happened in the past with the accidental consumption of wheat seedlings treated with hexachlorobenzene (HCB). Several thousand cases of hepatic porphyria occurred after incidences of mass poisoning in Iraq and Turkey. Of course, porphyria was neither the leading nor the most severe symptom of HCB poisoning (26,27).

Herbicides primarily target plant-specific enzymes and are thus generally of comparatively low toxicity to nontarget organisms. Acute intoxications mainly affect the central nervous system, with kidney effects being reported after long-term exposure to chlorophenoxy derivatives. From this group of substances, 2,4,5-T especially has been found to be contaminated with dioxin in the past, and a variety of health effects in former users have been attributed to it. The most exposed, however, were not farmers but American soldiers involved in the spraying of Agent Orange in Vietnam, and hepatic or renal disorders were not a major issue in these cases. The herbicide paraquat has become an infamous example of high mortality due to pulmonary fibro-sis together with liver and kidney failure. Although such cases usually relate to either accidental or suicidal oral intake of larger quantities, one case of lethal paraquat poisoning in a Japanese worker with an occupational history of spraying paraquat in a greenhouse has been reported (28,29).

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