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TRADE AND OTHER NAMES: Trade names for products containing demeton-s-methyl include Meta-Systox I,
Meta-isosystox, Azotox, Bay-18436, Bay-25/154, DSM, Duratox, Metasystox 55, Mifatox, and Persyst (1,2).
REGULATORY STATUS: Demeton-s-methyl is no longer registered for use in the United States (11).
INTRODUCTION: Demeton-s-methyl is a systemic and contact insecticide and acaricide that is a member of the
organophosphate family of chemicals. It is absorbed and translocated within the plant in sufficient concentrations to kill
insects that feed on the plant by sucking its juices. It is used to control aphids, sawflies, and spider mites in fruits,
vegetables, potatoes, cereals, ornamentals, and in forestry. Demeton-s-methyl replaces methyl demeton, a mixture of
demeton-s-methyl and demeton-o-methyl sold as Meta-Systox. Demeton-s-methyl is more toxic to insects than
demeton-o-methyl (1, 7). Classified as Category I - highly toxic, products containing demeton-s-methyl bear the SIGNAL
WORD: DANGER (3). It is available as an emulsifiable concentrate (1).
- Acute Toxicity: Demeton-s-methyl inhibits acetyl-cholinesterase, an enzyme critical to the normal function of the
nervous system. Symptoms of toxicity are similar to those caused by other organophosphate insecticides including
headaches, nausea, vomiting, diarrhea, sweating, and dizziness. In addition, symptoms in some cases of poisoning include
tremors, lack of coordination, and hiccough. With time, anorexia and loss of the ability to concentrate may occur (1, 5).
Demeton-s-methyl is non-irritating to the skin and eyes (10). The LD50 for demeton-s-methyl, the dose at which half of
the test animals who ate it died, is approximately 60 mg/kg for rats and 110 mg/kg for guinea pigs. The LD50 for rats
whose skin is exposed is approximately 85 mg/kg. The concentration in air that kills half of the rats exposed for four
hours, the LC50, is 500 mg/m3 of air (9).
- Chronic Toxicity: No information Available.
- Reproductive Effects: Demeton-s-methyl does not appear to cause reproductive effects. Daily oral doses of
oxydemeton (Metasystox R), a derivative of demeton, caused decreased cholinesterase in pregnant rats, as well as
decreased body weight. The females also developed tremors, but there was no evident effect on the fetuses(7).
- Teratogenic Effects: Demeton-s-methyl's capacity to cause teratogenic effects is not clear. Studies show that 10 mg/kg
of demeton, the parent compound of demeton-s-methyl, is mildly teratogenic when given to mouse embryos between 7
and 10 days old. It causes digestive, nervous, and skeletal problems, malformed digits and vertebrae, and cleft palate.
However, when daily doses of up to 4.5 mg/kg of oxydemetonmethyl, a metabolic product of demeton-s-methyl, are
given to pregnant rats from days 6 to 15 of gestation, there is no evidence of teratogenic effects (7).
- Mutagenic Effects: Test results indicate that demeton-s-methyl is mutagenic. Mutagenicity studies show effects on sex
chromosomes in fruit flies treated with 80 mg/kg of demeton-s-methyl. Microbes also mutated when exposed to 5
mg/plate of demeton-s-methyl (6).
- Carcinogenic Effects: Demeton-s-methyl is an organo-phosphate compound. Studies of other organo-phosphosphate
compounds show they do not share the chemical characteristics of most tumor causing compounds and most
organophosphate compounds tested do not cause tumors in rats and mice (1).
- Organ Toxicity: Chronic exposure to demeton-s-methyl can cause inner ear irritation and excess blood in the tissue of
respiratory organs. Rats receiving 15 daily applications of 5 mg of demeton-methyl, a mixture of demeton-s-methyl and
demeton-o-methyl, on their skin suffered liver damage and cholinesterase inhibition in the brain(6).
- Fate in Humans and Animals: Organophosphorus pesticides like demeton-s-methyl are rapidly absorbed into the body
through mucous membranes of the digestive tract, the respiratory system, and the skin. Demeton-s-methyl is broken
down in the body and rapidly eliminated in urine (2).
- Effects on Birds: The LC50 for Japanese quail is approximately 50 ppm, indicating that demeton-s-methyl is highly
toxic to this species (3).
- Effects on Aquatic Organisms: Demeton-s-methyl is moderately to slightly toxic to aquatic organisms. The LC50 for
rainbow trout exposed for 48 hours is 4.5 ppm (3). For carp and Japanese killifish, the LC50 is 10 ppm (2).
- Effects on Plants: Demeton-s-methyl is toxic to some ornamental plants, particularly chrysanthemum varieties. It is not
toxic to most other plants when used according to directions (2).
- Effects on Other Animals (Nontarget species): Demeton-s-methyl is toxic to bees (2).
- Breakdown of Chemical in Soil and Groundwater: Organophosphorus insecticides are relatively non-persistent in the
environment. Applied to crops and sometimes soil, they persist for only a few hours to a few months. Compounds in this
class react with the soil and bind well to soils with a high organic content. They do not move freely in wet soils and
leaching does not appear to be a major factor (8).
- Breakdown of Chemical in Surface Water: No information is currently available.
- Breakdown of Chemical in Vegetation: No information is currently available.
PHYSICAL PROPERTIES AND GUIDELINES: Demeton-s-methyl is incompatible with alkaline materials (10). It is
hydrolyzed rapidly in alkaline media and more slowly in acidic and neutral aqueous media (2). It is non-corrosive (10).
When heated to decomposition, demeton-s-methyl emits very toxic fumes(9).
- Appearance:Demeton-s-methyl is a pale yellow oil that has a sulfur-like odor.
- Chemical Name: S-[2-(ethylthio)ethyl]O,O-dimethyl phosphorothioate (2)
- CAS Number: 919-86-8
- Molecular Weight: 230.3
- Water Solubility: 3.3 g/l at 20 degrees C (2)
- Solubility in Other Solvents: Rapidly soluble in common polar organic solvents including dichloromethane, 2-propanol,
toluene and n-hexane (2, 4)
- Vapor Pressure: 40 mPa
- Partition Coefficient: 1.32
- Adsorption Coefficient: Not Available
- ADI: 0.0003 mg/kg (for sum of demeton-s-methyl, demeton-s-methylsulphon and oxydemeton-methyl) (2)
- MCL: Not Available
- RfD: Not Available
- PEL: Not Available
- HA: Not Available
- TLV: (TWA - 0.5 mg/m3 (10)), (ELR - Short term exposures should not exceed 1.5 mg/m3 for more than a total of 30
minutes during the weekday. Under no circumstances should exposure exceed 2.5 mg/m3 (10))
Bayer AG/ Miles
P.O. Box 4913
Kansas City, MO 64120
- Telephone: 816-242-2000
- Emergency: 816-242-2582
References for the information in this PIP can be found in Reference List Number 5
DISCLAIMER: The information in this profile does not in any way replace or supersede the information on the pesticide
product label/ing or other regulatory requirements. Please refer to the pesticide product label/ing.