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Chapter: Modern Medical Toxicology: Hydrocarbons and Pesticides: Pesticides

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Thiocarbamates - Fungicides

Examples include benomyl, benthiocarb (or thiobenzcarb), cycloate, diallate, ferbam, molinate, thiram, thiophanate, trial-late, zineb and ziram.

FUNGICIDES

These are compounds which kill fungi and moulds. Examples, thiocarbamates, captan, captafol, bavistin, vitavax, hexachlo-robenzene and sodium azide.

Thiocarbamates

·              Examples include benomyl, benthiocarb (or thiobenzcarb), cycloate, diallate, ferbam, molinate, thiram, thiophanate, trial-late, zineb and ziram.

·              Carbendazim (carbendazole), ETU, mancozeb, maneb, and vondozeb are benzimidazole (ethylenebisdithiocarba-mate or ethylenethiourea) compounds that are also used as fungicides.

Brands

·              Propineb: Antracol

·              Carbendazim: Bavistine, Benguard, Benfil, Dhanustin,Derosal, Fungi guard, JK Stein, Kilex, Paedistin Benomyl: Benlate, Benofit

·              Benthiocarb: Saturn

·              Mancozeb: Bayleton, Captofol, Captaf, Dithane M-45,Dhanuka M-45, Hilthane, Indofil M-45, Kavach, Krilaxlyl, Luzem, Manzate, Ridomil, Sparsh, Uthane, Vijay M-45, Zeb M, Zeb 75, Zebatane

·              Carbendazim + Mancozeb: CM-75

·              Carbendazim + Iprodione: Quindal

·              Mancozeb + Metalaxyl: Master, Matca, Pestmil

·              Mancozeb + Thiophanate methyl: Roko

·              Thiophanate methyl: Cover

·              Zineb: Indofil

·              Ziram: Cumun-L, Zinax, Ziram

·              These compounds are used as fungicides and have relatively low toxicity. They do not inhibit acetylcholinesterase (unlike carbamates).

Sources and Uses

·      Most of these compounds are used as fungicides. Formulations are widely used for pest control in home gardens and in commercial agriculture.

·      Some are found in suntan and antiseptic sprays, and some medicated cleansing agents. Some are also used in the plastic industry as an antioxidant, and as a rubber accel-erator.

·      Carbendazim is also used as a preservative in the paint, textile, papermaking and leather industries. Carbendazim is also currently undergoing clinical trials in adult patients with advanced malignancies (i.e. breast cancer, melanoma, colon cancer).

Usual Fatal Dose

Ingestion of > 200 ml is likely to produce severe toxicity.

Clinical Features

·      Absorption of these agents across the skin and GI lining is probably slower than absorption of the organochlorine and ester insecticides. Exposure results in vomiting, diarrhoea, abdominal pain, weakness, conjunctivitis, vertigo, seizures, and rarely renal failure.

·      Other manifestations have included CNS depression, extrapyramidal effects, and neuropathy.

·      These agents are often compounded with hydrocarbon-based solvents, which may be responsible for toxicity. Some agricultural workers experience upper respiratory congestion, hoarseness, and cough if they breathe sprays or dusts containing these compounds.

·      To some degree, all of these chemicals, the sulfur-containing in particular, are irritating to the skin and mucous membranes. Thiram is related to disulfiram and produces a similar reaction with ethanol.

·      Although detailed pharmacokinetic studies of these compounds are not available, there is indirect evidence (minimal tissue storage after dosing) that these chemicals are rapidly metabolised and/or excreted by humans, usually within hours or days of absorption.

·      Teratogenecity and carcinogenecity:

o     In female rats exposed to carbendazim during gesta-tion, significant maternal toxicity, embryonal lethality, teratogenic effects, and retarded foetal development were reported.

o     Ethylene thiourea (ETU): A contaminant and break-down product of ethylene bisdithiocarbamate fungi-cides (maneb, nabam, zineb) is a recognised carcinogen in animals. Hepatomas, lymphomas, and thyroid carci-nomas have been described.

Treatment

·     Activated charcoal can be administered.

·              Gastric lavage is recommended if done early and cautiously.

·              Intravenous fluids may be useful in restoring extracellular fluid volume if this has been depleted by vomiting and diarrhoea.For convulsions: Attempt initial control with a benzodiaz-epine (diazepam or lorazepam). If seizures persist or recur administer phenobarbitone.

 

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