E X T O X N E T
Extension Toxicology Network
A Pesticide Information Project of Cooperative Extension Offices of
Cornell University, Michigan State University, Oregon State University, and
University of California at Davis. Major support and funding was provided
by the USDA/Extension Service/National Agricultural Pesticide Impact
Publication Date: 9/95
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).
Demeton-s-methyl is no longer registered for use in the United States
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).
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).
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
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).
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 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).
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 a pale yellow oil that has a sulfur-like odor. It 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).
|CAS No.: ||919-86-8
|Chemical Name: ||S-[2-(ethylthio)ethyl]O,O-dimethyl phosphorothioate (2)
|Solubility in water: ||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)
|Boiling Point: ||74 degrees C at 0.15 mm Hg (10)
|Volatility: ||3.6 x 10 to the minus 4 mm Hg at 20 degrees C (10)
|ADI: ||0.0003 mg/kg (for sum of demeton-s-methyl, demeton-s-methylsulphon and oxydemeton-methyl) (2)
|NOEL: ||1 mg/kg (rats) (2)
|TLV-TWA: ||0.5 mg/m3 (10)
|TLV-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
Review by Basic Manufacturer:
Comments solicited: October, 1994
Comments received: January, 1995
Hayes Jr., W. R. and E.R. Laws, Jr. (eds.) 1991. Handbook of Pesticide
Toxicology. Academic Press, Inc. New York, NY.
The Agrochemicals Handbook, Third Edition. 1994. Royal Society of
Chemistry Information Systems, Unwin Brothers Limited. Surrey, England.
Meister, R.T. 1994. Farm Chemicals Handbook '94. Meister Publishing
Company, Willoughby, OH.
Smith, G.J. 1993. Toxicology & Pesticide Use in Relation to Wildlife:
Organophosphorus & Carbamate Compounds. C.K. Smoley. Boca Raton, FL.
Budavari, Susan (ed.). 1989. The Merck Index, Eleventh Edition. Merck
and Company Inc. Rahway, NJ.
National Institute for Occupational Safety and Health (NIOSH). 1993.
Registry of Toxic Effects of Chemical Substances (RTECS). NIOSH. Cincinnati,
Chambers, J. E. and Patricia Levi. 1992. Organophosphates Chemistry,
Fate, and Effects. Academic Press, Inc. New York, NY.
Amdur, M. O., John Doull & Curtis Klaassen. 1991. Casarett and Doull's
Toxicology. Pergamon Press. New York, NY.
Sax, N. I. 1984. Dangerous Properties of Industrial Materials, Sixth
Edition. Van Nostrand Reinhold Co. New York, NY.
U.S. Department of Health and Human Services. 1993. Hazardous
Substance Data Base. HHS. Washington, DC.
U.S. EPA Region 5. Phone call with David Star. August 31, 1994.