PRINCIPLES OF TOXICOLOGY - Biology East Borneo

358 PROPERTIES AND EFFECTS OF PESTICIDESOOHOCCH 2 NH CH 2 POHOHFigure 15.6 Glyphosate.Diquat causes less dermal irritation and injury than does paraquat, and diquat is not selectivelyconcentrated in pulmonary tissue like paraquat. Diquat, in contrast to paraquat, causes little to no injuryto the lungs; however, diquat has an effect on the central nervous system, whereas paraquat does not.The mechanism of action of diquat is thought to be similar to that of paraquat, involving the productionof superoxide radicals that cause lipid membrane destruction. Dermal exposure to sufficient levels ofdiquat can cause fingernail damage and irritation of the eyes and mucous membranes. Intoxication bydiquat via the oral route has reportedly caused signs and symptoms including gastrointestinal irritation,nausea, vomiting, and diarrhea. Both paraquat and diquat are reportedly associated with renal toxicity.There is no known specific antidote for either paraquat or diquat poisoning.Glyphosate (Round-Up) [N-(phosphonomethyl) glycine] (see Figure 15.6) is a widely usedherbicide that interferes with amino acid metabolism in plants. In animals it is thought to act as a weakuncoupler of oxidative phosphorylation. Glyphosate is moderately absorbed through the gastrointestinaltract, undergoes minimal biotransformation, and is excreted via the kidneys. There have beenseveral reports in the literature of intoxications, typically resulting from accidental or suicidal ingestion,following overexposure to the glyphosate-containing product Round-Up. Various signs and symptomsinclude gastro-intestinal irritation and damage, as well as dysfunction in several organ systems (e.g.,lung, liver, kidney, CNS, and cardiovascular system). It has been proposed that the toxicity seenfollowing intoxication with Round-Up is due to the surfactant agent in the commercial product. Onestudy conducted determined that the irritative potential of the commercial preparation of Round-Upis similar to that of baby shampoo.TriazinesExamples of triazine and triazole herbicides include atrazine (2-chloro-4-ethylamino-6-isoproplyamine-s-triazine),propazine, simazine [2-chloro-4,6-bis(ethylamino)-s-triazine], and cyanazine[2-chloro-4-(1-cyano-1-methylethylamino)-6-ethylamino-s-triazine]. Triazine herbicideshave relatively low toxicity, and no cases of systemic poisoning have appeared to have been reported.Occasional reports of dermal irritation from exposure to triazine herbicides has been reported in theliterature.15.5 FUNGICIDESFungicides are compounds that are used to control the growth of fungi and have found uses in manydifferent products, from their use to protect grains after harvesting while they are in storage to theiruse in paint products.Pentachlorophenol, also known as penta, is used as a wood preservative for fungus decay or againsttermites, as well as a molluscicide. Trade names of pentachlorophenol include Pentacon, Penwar, andPenchlorol (Figure 15.7).Pentachlorophenol is readily absorbed via the skin, lung, and gastrointestinal tract. Pentachlorophenoland its biotransformation products are excreted primarily via the kidneys. The biochemicalmechanism of action of pentachlorophenol is through an increase in oxidative metabolism from theuncoupling of oxidative phosphorylation. This increase in oxidative metabolism in poisonings can leadto an increase in body temperature. In fatal cases of poisoning from pentachlorophenol, body