Pesticide Fact Sheet
Carbaryl is an extremely popular lawn care pesticide in Canada, sold under the trade name of Sevin. It is considered very toxic with an LD50 of 225mg/kg. A dose of 18g or two-thirds of an ounce would be enough to kill a 70kg or 154 pound adult. 
How It Works
Carbaryl is a carbamate insecticide. Like all members of the carbamate family, carbaryl works by attacking the nervous system. Specifically, it inhibits the essential action of an enzyme called acetylcholinesterase (AChE). AChE works to break down another chemical, acetylcholine, which is essential in transmitting impulses between nerves. Therefore, when carbaryl is used, AChE becomes unable to break down acetylcholine, which consequently accumulates in nerve cells. This abnormal acetylcholine build-up can cause incoordination, rapid twitching, incoordination, paralysis and death.,
Acute effects of carbaryl exposure in humans includes malaise, muscle weakness, dizziness, sweating, headache, salivation, nausea, diarrhea, incoordination, slurred speech and a depression of breathing combined with excess fluid in the lungs. With high exposure the most common cause of death is the pulmonary edema, the combination of too much lung fluid and not enough air.
Chronic effects of very small doses, less than one one-thousandth of the LD0, include decreasing the kidneys ability of adsorb amino acids, the links on protein chains, and abdominal cramping. Similar doses have been shown to cause kidney abnormalities in rats and dogs, reduced heart rates, liver pathologies and reduced blood clotting in rats. Children, pregnant women, older persons and individuals with compromised immune system are more prone to the effects of carbaryl.
Carbaryl reacts with a striking number of other products which make its use all the more dangerous. Carbaryl reacts with many other pesticides including phenoxy herbicides like 2,4-D, the wood preservative Pentachlorophenol, the anti-ulcer drug Tagamet (cimetidine), and the histosomiasis drug Niridazole.
Effects to the Environment and Wildlife
Carbaryl has deleterious effects on a variety of wildlife including beneficial arthropods, birds, fish, earthworms, plants and bacteria.
Because it is a broad spectrum insecticide with a mode of action common to the majority of living organisms, its target insects (mites) are not the only organism killed by its use, but numerous beneficial insects. This has been found in both agricultural and non-agricultural systems.
Toxicity to fish is varied but can cause death in concentrations as low as 2-16ppm in water. Sublethal effects such as damage to gill and liver cells, kidney lesions were visible at concentrations less than 1ppm. Synergistic effects with other pesticides such as 2,4-D, rotenone, or pentachlorophenol increased toxicity in fish.
One of the chemicals used in the manufacture of carbaryl is methyl isocyanate (MIC). On December 3, 1984, a gas leak occurred at the Union Carbide factory in Bhopal where both carbaryl and aldicarb (another carbamate insecticide), were produced. MIC is slightly lighter than water but heavier than air, so it escapes into the atmosphere and stays low to the ground. Approximately 40 tons of MIC poured out of the leaky tank for 2 hours, escaping into the air and spreading within eight kilometres downwind over a city of nearly 900,000 people.
Although estimates range as high as 5,000, at least 3,000 people died in the immediate aftermath, and over half a million seriously injured within the first three days. Since then at least 20,000 other deaths have occurred. Despite the list of damage MIC exposure can cause: eye and lung damage, emphysema, gastrointestinal problems, vision problems, neurological disorders involving memory and motor skill problems, muscoskeletal problems and gynecological problems and the number of deaths and chronic health problems that occurred, Union Carbicide, now Dow Chemical, has claimed that MIC is a mild throat and ear irritant.
The insecticide carbaryl has a staggering number of acute and chronic adverse effects to non-target beneficial insects, to other wildlife such as birds, and fish, and to humans. Health effects range from lowered sperm counts, depression and diarrhea, to severe chronic ailments and death.
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