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Methamidophos — toxicity, side effects, diseases and environmental impacts

Wednesday, November 29, 2017 by

Methamidophos is an active systemic organophosphate insecticide. It was registered for use in the U.S. on commercial crops, but was voluntarily canceled in 2009. Methamidophos is a potent acetylcholinesterase inhibitor, effective against chewing and sucking insects, used to control aphids, flea beetles, worms, thrips, cabbage loopers, leafhoppers, and many others. This off-white crystalline chemical works by decreasing the acetylcholinesterase activity in nervous system function, which is essential in the normal transmission of nerve impulses. It is used on crops like potatoes, cotton, tomatoes, broccoli, cauliflower, celery, and tobacco. It is available in soluble concentrates, wettable powders, granules, and emulsifiable concentrates.

This insecticide is highly soluble in water, and is acutely toxic to bees, birds, fish and other aquatic life forms. Water bodies that are contaminated with methamidophos will clear out after a few weeks. Methamidophos is toxic orally, dermally, and via the inhalation route of exposure. In lab experiments, oral doses of this chemical resulted in fatality for guinea pigs, rabbits, rats, and mice.

Exposure to methamidophos may occur through food intake, due to the fact that methamidophos is highly residual. Agricultural personnel have a higher rate of exposure, potentially via ingestion, dermal absorption, and inhalation.

It is manufactured by the Bayer Agricultural Products company. Other names for methamidophos include O,S-Dimethylphosphora-midothiolate; C2H8NO2PS; 10265-92-6; Monitor; Tamaron; Filitox; Tamanox; Tarn; Patrole; Metamidofos Estrella; Methamidophos 60 WSC Methedrin 60; Morithion; and Red Star Alloran.

List of known side effects

Methamidophos may cause intoxication and mortality when inhaled, ingested, absorbed through the skin and eyes. Inhalation may result in tightness of the chest, wheezing, blurred vision, headaches, miosis (excessive constriction of the pupil), tearing, and runny nose. Ingestion of methamidophos can cause nausea, vomiting, diarrhea, and abdominal cramps. Skin absorption causes sweating and muscle twitching on the area affected. Other side effects of methamidophos exposure are weakness, shakiness, blurred vision, confusion, fluctuating heart rates, convulsions, coma, and cessation of breathing.

In Sri Lanka, a person who experienced intermediate intoxication experienced paralysis of limbs, neck, and respiratory muscles, only after 24 to 96 hours after exposure. After two to four weeks, delayed neurological problems have been documented. Organophosphate poisoning can be counteracted by atropine antidotes.

Body systems affected by methamidophos

Methamidophos poisoning affects the respiratory system, the digestive and excretory system, the central nervous system, and the reproductive system (in laboratory tests). It is also weakly mutagenic, causing some changes in genetic make-up. There is no evidence of carcinogenicity in humans as of the moment. This chemical is rapidly absorbed in the stomach, lungs, and skin, and is primarily eliminated in the urine.

Items that may contain methamidophos

Methamidophos residue may exist in food items such as broccoli, cauliflower, Brussels sprouts, celery, beets, potatoes, hops, corn, tomatoes, and other vegetables. Fruits including pome, stone, and citrus may also have this residue. Other crops like cotton may have traces of methamidophos.

How to avoid methamidophos

Avoid eating commercial agricultural products as listed in the items that contain methamidophos. Avoid visiting commercial farms or sites that use this pesticide. Keep away from children at all costs.

Always wear protective clothing and use protective gear to avoid methamidophos poisoning. This includes boots, chemical gloves, glasses or goggles, coveralls, and a full-head respirator. Restrict storage areas to trained personnel only, and keep containment under lock and key. Spills must immediately be cleaned and sanitized to avoid second-hand injury.

In cases of inhalation, move victim to fresh air. For ingestion, induce vomiting if there are no petroleum distillates with the chemical. For skin and eye contact, flush with clean water. For all cases mentioned, contact emergency medical services immediately, or transport the victim to the nearest emergency department.

Where to learn more


Methamidophos is acutely toxic to humans.

Methamidophos is fatal to environmental life forms, especially aquatic species and bees.

Methamidophos poisoning may result in death.

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