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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 Assessment Program.


Publication Date: 9/93


Some trade names include Caparol, Gesagard, Prometrex, Primatol Q and Mercasin.


Prometryn is classified by the U.S. Environmental Protection Agency (EPA) as a general use herbicide. Products containing prometryn must bear the EPA signal words "Caution" or "Warning" (1).


Prometryn is a selective herbicide which controls annual grasses and broadleaf weeds in cotton and celery. It inhibits photosynthesis. Prometryn is available in wettable powder and liquid formulations (21).



In humans, prometryn is slightly to moderately toxic (4, 5). It is harmful if swallowed, and exposed workers may complain of sore throat and nausea (12). Eye and skin contact with the herbicide should be avoided, as should inhalation of dust, and contamination of food and feed (17). Prometryn mixers, loaders, and applicators receive the most exposure from skin and eye contact, as well as from inhalation (13). Occupational exposure to triazine herbicides, the class of herbicides within which prometryn is included, may produce some generalized bodily, or 'systemic,' toxicity. Workers in some triazine manufacturing plants suffer from skin irritation. Finished triazines have not been reported to cause significant skin or mucous membrane irritation (12). Prometryn was not irritating to rabbit skin. Application of 80 mgto rabbit eyes was mildly irritating (22).

The amount of a chemical that is lethal to one-half (50%) of experimental animals fed the material is referred to as its acute oral lethal dose fifty, or LD50. The oral LD50 for prometryn in rats is 3,750 to 5,235 mg/kg, in mice is 3,750 mg/kg, and in rabbits is 278 mg/kg. Animals that have been acutely poisoned by prometryn exhibit sedation, muscle incoordination, breathing difficulty, bulging eyes, constricted pupils, diarrhea, excessive urination, and convulsions. When technical prometryn is applied to the intact skin of rabbits, it is not irritating. The dermal LD50 in rabbits is 2,000 to greater than 3,100 mg/kg, and in rats it is 3,100 mg/kg. The prometryn formulation, Caparol 80W, is a mild eye irritant and a slight skin irritant in rabbits. The lethal concentration fifty, or LC50, is that concentration of a chemical in air or water that kills half of the experimental animals exposed to it for a set time period. The 4-hour LC50 for prometryn in rats is 5,170 mg/m3. No deaths occurred in rats exposed to aerial concentrations of 4,400 mg/m3 for 4 hours, or in mice exposed to 25 mg/m3 for 2 hours (1, 5, 20, 21, 22).


The results of various long-term feeding studies do not indicate obvious, nor severe, toxicity from prometryn exposure. Chronic oral feeding studies for 2 years, during which rats and dogs received daily doses of prometryn, did not result in gross or microscopic signs of systemic toxicity. Ingestion rates were as high as 62.5 mg/kg/day for rats, and 3.75 mg/kg/day for dogs (17, 19). Two out of 24 rats died after daily feeding of prometryn at a rate of 50 mg/kg body weight/day for 90 days (6).

NOEL: 150 ppm in a two-year feeding study with dogs (equivalent to 3.75 mg/kg body weight, and this is the basis for the ADI established by EPA (16).

PADI: 0.004 mg/kg/day (based on a two-year dog feeding study with a NOEL of 3.75 mg active ingredient/ kg/day (14).

Reproductive Effects

The potential for prometryn to negatively affect reproduction cannot be determined until more chronic studies are conducted and submitted by producers to EPA for review (13). Reduced maternal body weights and decreased food consumption were observed in rats fed 250 mg/kg body weight. In a three- generation reproduction study, no reproductive effects were seen in rats fed up to 100 ppm (16).

Teratogenic Effects

The teratogenic potential of prometryn cannot be determined until more chronic toxicity studies are conducted and reviewed (14). No teratogenic effects were seen in the offspring of rats fed 250 mg/kg of body weight, the highest dose tested (16).

Mutagenic Effects

Eleven different tests for mutagenicity involving hamsters, bacteria or mammalian cell cultures have all produced negative results (20).

Carcinogenic Effects

The tumor-causing, or oncogenic, potential of prometryn cannot be determined until more chronic studies are conducted and submitted to the EPA for review (14). Based on a two-year feeding study with rats, it was concluded that prometryn is not a carcinogen in this species at feeding levels up to at least 62.5 mg/kg/day (16).

Organ Toxicity

In a two-year feeding study with dogs, 37.5 mg/kg/day produced degenerative changes in liver and kidney tubules, and atrophy of the bone marrow was observed. Weight loss, breakdown of the fat cells of the liver, organ congestion, and severe circulatory disorders were seen in a 28-day feeding study in rats (16).

Fate in Humans and Animals

While the breakdown of prometryn is not adequately understood, available data indicate that, in rats, most of the herbicide is excreted in urine and feces within 48 hours of administration (13). No detectable residues of prometryn or its breakdown products were found in whole milk samples taken from cows that were fed 0-100 ppm in their diet for 21 days. Nor were prometryn or metabolic residues of prometryn found in the muscle, fat, blood, liver, kidney and other organs of sheep and cattle that were fed up to 100 ppm of the herbicide for four weeks (3). Prometryn is part of a class of herbicides classified as triazine herbicides which are well absorbed by the mammalian gut, and probably across the skin (12).


The EPA cannot fully assess the effects of prometryn on fish and wildlife because of insufficient available data (14).

Effects on Birds

Prometryn is practically nontoxic to birds (13, 19). Technical prometryn has a 5 to 7 day dietary LC50 of 16,140 ppm in quail and 38,736 ppm in ducks (17). In mallards, its LD50 is greater than 4640 mg/kg. In mallards the LD50 is 34,512 ppm (13).

Effects on Aquatic Organisms

Prometryn is moderately toxic to fish (13). The 96-hour LC50 in rainbow trout is 2.5 to 2.9 mg/l, 10.0 mg/l in bluegill sunfish, 3.5 mg/l in goldfish, and 8 mg/l in carp (6, 14, 21).

It is also slightly toxic to freshwater invertebrates (14). The toxicity of prometryn to aquatic organisms was tested in plankton, green algae and guppies. It was highly toxic to the guppies and acted as a strong poison in algae, through inhibition of photosynthesis (12). A 19% decrease in shell growth was observed in oysters exposed to 1.0 ppm of the herbicide for 48 hours. Pink shrimp were unaffected by exposure to 1.0 ppm of the herbicide for 48-hours (10).

Effects on Other Animals (Nontarget species)

Prometryn is non-toxic to bees (21).


Breakdown of Chemical in Soil and Groundwater

Prometryn binds readily to soils with high clay and organic matter content. Its movement to ground water is limited in these soil types (15). Available data indicate that this herbicide is mobile in sandy soils and moderately mobile in sandy loam soils. Its mobility appears to be related to organic content of the soil: the lower the organic content, the more mobile prometryn is in soil (13). Prometryn is adsorbed to a greater extent than most other commercial triazine herbicides (17). Field leaching studies have shown that prometryn stays in the top 12 inches of treated soil (2).

The action of soil microorganisms is important in the breakdown of prometryn in soil. Several soil microorganisms have been reported to utilize the herbicide as a source of energy, nitrogen and sulfur (17). No change was found in the number of microorganisms in soil treated for four years at a rate of 5.4 lb/acre (10). The amount of the herbicide that evaporates, from the soil increases as soil temperature and soil moisture content increase, however volatilization is not significant under field conditions (15, 24).

Prometryn persists in the soil from one to three months (6, 15). Its soil half-life is 60 days (23). Following multiple annual applications of the herbicide, prometryn activity can persist for 12-18 months after the last application (2). It will persist longer under dry or cold conditions which are not conducive to chemical or biological activity (24).

Breakdown of Chemical in Water

Prometryn formulations must not be applied directly to water or wetlands such as swamps, bogs, or marshes. Water bodies can be contaminated by inappropriate cleaning of equipment, or disposal of wastes associated with this herbicide (14). No significant hydrolysis, or breakdown in water, was found when prometryn was tested over a period of 28 days in water with a pH ranging from 5 to 9, and at a variety of test temperatures (2).

Breakdown of Chemical in Vegetation

Prometryn is absorbed through both the foliage and roots of plants. It is translocated from the roots to the leaves in plants, accumulating in the growing shoots (3). The herbicide appears to penetrate foliage rapidly, minimizing its removal from leaves by rain. Plant removal or degradation is slow and does not appear to be a major factor in the dissipation of prometryn (17).

Postemergence treatments of prometryn must be directed carefully to avoid damage to desirable plants; it can be extremely phytotoxic, or poisonous to plants when it comes in contact with some varieties (17).


Prometryn is a white, crystalline solid (21). It is stable in neutral, slightly acidic, or slightly alkaline media but is hydrolyzed under more strongly acidic or basic conditions (7). Prometryn is noncorrosive under normal application conditions (1). It is stable under normal temperatures and pressures, does not ignite readily, but may burn if exposed to heat or flame. Thermal decomposition products may include toxic oxides of carbon, nitrogen or sulfur (22).

Occupational Exposure Limits:

No occupational exposure limits for prometryn have been established by OSHA, ACGIH or NIOSH (22).

Physical Properties:

CAS #: 7287-19-6
Specific gravity: 1.157 (22)
Melting point: 118-120 degrees C (21)
H20 solubility: 33 to 48 ppm at 20 degrees C (14, 18, 22)
Solubility in other solvents: readily soluble in organic solvents including ethanol, methanol, acetone, dichloromethane and toluene (13, 22).
Melting point: 118-120 degrees C (18)
Vapor pressure: 1.0 x 10 to the minus 6 mm Hg at 20 degrees C, 4.7 x 10 to the minus 5 mm Hg at 50 degrees C (17, 22)
Koc: 500 g/ml (23)
Chemical Class/Use: Substituted triazine herbicide


Ciba-Geigy Corporation
Agricultural Division
PO Box 18300
Greensboro, NC 27419-8300

Review by Basic Manufacturer:

Comments solicited: January, 1992
Comments received: April, 1992


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  3. Dynamec Corporation. 1983. Prometryn, herbicide. Compiled for U.S. Environmental Protection Agency. Rockville, MD: Dynamec Corp.
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  12. TOXNET. 1985. National library of medicine's toxicology data network. Hazardous Substances Data Bank (HSDB). Public Health Service. National Institute of Health, U. S. Department of Health and Human Services. Bethesda, MD: NLM.
  13. U.S. Environmental Protection Agency. 1987 (Mar.) Guidance for the reregistration of pesticide products containing Prometryn as the active ingredient. Washington, DC.
  14. ______. 1987. (Mar.) Pesticide fact sheet: Prometryn. Office of Pesticide Programs. Office of Pesticides and Toxic Substances. (TS-766C). Washington, DC.
  15. _____. 1983. Food and Drug Administration, Environmental Fate Branch surveillance index profile: Prometryn. Hazard Evaluation Division. Washington, DC.
  16. _____. 1982 (Aug. 9). Surveillance index support document. Toxicity summary: Prometryne. Washington, DC.
  17. Weed Science Society of America. 1983. Herbicide Handbook. Fifth edition. Champaign, IL: WSSA, Herbicide Handbook Committee.
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  22. Occupational Health Services, Inc. 1991 (Feb. 21). MSDS for prometryn. OHS Inc., Secaucus, NJ.
  23. USDA SCS. 1990 (Nov.). SCS/ARS/CES Pesticide Properties Database: Version 2.0 (Summary). USDA - Soil Conservation Service, Syracuse, NY.
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