HERBICIDES AND FUNGICIDES
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Herbicides
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Herbicides are used routinely to control noxious plants.
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Vegetation treated with herbicides at proper rates normally will not be hazardous.
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Herbicides are of two types – Inorganic and organic synthetic
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Inorganic herbicides include – Arsenicals, ammonium sulfamate, borax and sodium chlorate
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Organic herbicides include -
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Dipyridyl compounds or quaternary ammonium herbicides
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Carbamate and thiocarbamate compounds
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Aromatic/benzoic acid compounds
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Phenoxyacetic and phenoxybutyric compounds
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Oinitrophenolic compounds
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Organophosphate compounds
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Triazolopyrimidine compounds
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Phenyl or substituted urea compounds
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Polycyclic alkanoic acids
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Sulfonylurea compounds
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Animals get exposed to herbicides from
Phenoxy herbicides
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2,4-Dichlorophenoxyacetic acid (2,4-D) and 2,4,5 trichlorophenoxyacetic acid (2,4,5 – T)
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2,4,5 trichlorophenoxyacetic acid is commonly known as ‘agent orange’ as it was used as defoliating agents in the Vietnam War
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It exerts its toxic effects on plants by blocking the action of plant growth hormones
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It is a relatively non toxic herbicide to humans and animals.
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They produce reproductive toxicity in cattle and hepato carcinoma in laboratory animals.
Dipyridyl herbicides
Paraquat
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A non selective contact herbicide, used extensively in Asian countries
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It is poorly absorbed from the gut due to 2 positive charges
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If it is absorbed into the blood stream, the lung is the major target organ for toxicity.
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The shape of the paraquat molecule is perfect to be a substrate for specific uptake systems present in Type II alveolar cells and
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There is abundant O 2 in the lungs
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The toxic effects on the lung include: Haemorrhage oedema, damage to type II alveolar cells and fibrosis.
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The toxic effects are stow to develop (3 to 4 weeks) since paraquat is poorly absorbed from the gut.
Treatment of paraquat toxicity
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If ingested: Gastric lavage and use of activated charcoal
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I n an emergency, clay can be used as it contains bentonile which is a negatively charged compound. This binds to paraquat (which is positively charged) to form an insoluble complex which is excreted in the faeces.
Dinitro compounds
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Act by interfering with electron transport chain of energy metabolism.
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Uncoupling of oxidative phosphorylation occurs and all the cellular energy is converted in the form of heat.
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Causes severe hyperthermia.
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Ruminal microflora reduces the dinitro compounds to diamine metabolites and this induces methaemoglobinaemia.
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Treatment is symptomatic and antipyretics are contraindicated.
Fungicides
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Used to prevent or treat fungal infections in plants or plant products.
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They are used to protect tubers, fruits and vegetables during storage.
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Soil fungicides are used at the time of planting.
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They are applied directly to ornamentals, trees, field crops, cereals and turf grasses.
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Low toxicity of modern fungicides generally prevent poisoning in animals.
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Misuse, accidents and carelessness are the major causes of toxicosis in pets and livestock.
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Fungicides vary in toxicity from barely toxic to highly lethal.
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Most available data are for laboratory animals; little information is available for farm animals and pets.
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Fungicides are commonly marketed and used in combination with other insecticides.
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The carriers or solvents, also known as ‘inert ingredients’, may be toxic.
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Clinical signs are often nonspecific may include anorexia, depression, weakness and diarrhea.
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Chemical analysis of treated or contaminated feeds and forages is usually more effective.
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Lesions, that are usually mild or generalized include gastroenteritis (acute exposure), rumen stasis and hepatic, renal and pulmonary congestion.
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Fumigants
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Fumigants are extremely toxic gases used to protect stored products, especially grains and to kill soil nematodes.
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These materials are applied to storage warehouses, freight cars and houses infested with insects .
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They present a special hazard due to inhalation exposure and rapid diffusion into pulmonary blood; thus extreme care must be taken when handling and applying this class of pesticides.
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All fumigants are classified as restricted use compounds and require licensed applicators to handle them.
Phospine (PH 3 )
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Used as a grain fumigant to kill weevils, nematodes, fungi
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It is a gas generated by the reaction of moisture (found in the grain) with aluminium phosphide (AlP 3 )
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Aluminium phosphide is added to the grain as satchels or tablets.
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The PH 3 formed is heavier than air, therefore it sinks down through the grain rather than rising up and polluting the atmosphere.
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Phosphine has the odour of rotting fish.
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Toxic symptoms include:
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Pulmonary oedema
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Ventricular arryhthmias
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Kidney damage
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Treatment of phosphine poisoning is based on treating the symptoms.
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