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: 9/93
TRADE OR OTHER NAMES
Some trade names include Caparol, Gesagard, Prometrex, Primatol Q and
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).
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).
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).
Eleven different tests for mutagenicity involving hamsters, bacteria or
mammalian cell cultures have all produced negative results (20).
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).
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
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).
PHYSICAL PROPERTIES AND GUIDELINES
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
Occupational Exposure Limits:
No occupational exposure limits for prometryn have been established by
OSHA, ACGIH or NIOSH (22).
|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
PO Box 18300
Greensboro, NC 27419-8300
Review by Basic Manufacturer:
Comments solicited: January, 1992
Comments received: April, 1992
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