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Pesticides include insecticides, herbicides, and rodenticides.1 Pesticide toxicity results from intentional, accidental, and occupational exposures. More than 300,000 pesticide-poisoning deaths occur each year worldwide, with insecticides accounting for the majority of deaths.2 Pesticides are marketed as multiple formulations, often under shared brand names; therefore, complex clinical syndromes can result from exposure to both active and other ingredients. Ingredients in proprietary formulations, such as petroleum distillates, are inert to pests during typical exposures, but can be toxic to humans, especially with excessive amounts. Pesticides have class-specific toxicities, with many having both local and systemic effects. Management often includes consultation with a hazardous materials and toxins database or with a poison control center. Supportive care is of utmost importance in pesticide poisonings, but for some compounds, antidotes are essential.
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The World Health Organization classifies pesticides according to toxicity based on the median lethal dose for oral and dermal exposure in rats. This classification has been criticized because human case-fatality rates display large variation for compounds within the same chemical and/or World Health Organization toxicity classification.3 Toxicity classification should not be used to predict severity after human exposure.
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Chemical insecticides are toxic to the nervous system, with acute and chronic manifestations, as well as delayed sequelae after acute exposure. Six major classes of insecticides are in common use (Table 201-1). Other compounds used to control insects include repellants.
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Commonly used organophosphates include diazinon, acephate, malathion, parathion, and chlorpyrifos and many others in different countries. Organophosphate and carbamate compounds are the insecticides most commonly associated with systemic illness.4,5 Potency among organophosphates varies; highly potent compounds, such as parathion, are used primarily in agriculture, whereas those of intermediate potency, including coumaphos and trichlorfon, are used in animal care. Diazinon and chlorpyrifos were phased out from household use in the United States in 2000 due to neurotoxicity, particularly on the developing brains of children, but they continue to be used in many other parts of the world.6 The organophosphate structure can be modified into chemical agents of mass destruction (see chapter 8, Chemical Disasters).
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Organophosphate poisoning results primarily from accidental exposure in the home, recently sprayed or fogged areas using pesticide applicators, agriculture, industry, and the transport of these products.4 Inadvertent exposure can occur from flea-dip products in pet groomers and children and from contaminated food. In addition, these chemicals are involved in intentional poisonings from homicides and suicides.7 Systemic absorption of organophosphates occurs by inhalation and after mucous membrane, transdermal, transconjunctival, and GI exposure.
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