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EXTOXNET primary files maintained and archived at Oregon State
Revised June 1996
Trade and Other Names:
Trade names include Caparol, Gesagard, Mercasin, Promet,
Prometrex, and Primatol Q.
Prometryn is a slightly to moderately toxic compound which is
classified as a member of toxicity class II or III, depending on
the formulation. It is classified as a General Use Pesticide
(GUP). Labels for products containing prometryn must bear the
Signal Words CAUTION or WARNING, depending on the formulation.
Prometryn is a selective herbicide which controls annual grasses
and broadleaf weeds in a variety of crops including cotton and
celery. It inhibits photosynthesis in susceptible species.
Prometryn is available in wettable powder and liquid
is available in wettable powder and liquid formulations.
- Acute toxicity: Prometryn is slightly to
practically non-toxic by ingestion, with reported oral
LD50 values of 3750 to 5235 mg/kg in rats, 3750 mg/kg in
mice, and greater than 2020 mg/kg in rabbits [6,15]. Via
the dermal route, it is slightly toxic with reported
dermal LD50 values of greater than 2000 mg/kg to greater
than 3100 mg/kg in rabbits [6,15]. Technical prometryn
does not cause skin irritation in rabbits or skin
sensitization in guinea pigs, and may cause slight eye
irritation in rabbits . Some formulations (e.g.,
Caparol), may be mild eye irritants and/or slight skin
irritants in rabbits [6,15]. The 4-hour LC50 for
prometryn in rats is 5.2 mg/L . Symptoms of high
acute exposure may include sedation, muscle
incoordination, breathing difficulty, bulging eyes,
constricted pupils, diarrhea, excessive urination, and
- Chronic toxicity: The results of
long-term feeding studies do not indicate obvious, nor
severe, toxicity from prometryn exposure. Rats fed
dietary doses of 37.5 mg/kg/day and dogs given 4
mg/kg/day over a 2-year period didn't show observable
gross or microscopic signs of systemic toxicity .
Effects which occurred at higher dose rates in these
animals included changes in relative weights of the
kidney and liver .
- Reproductive effects: In a
three-generation study, no reproductive effects were seen
in rats fed up to 5 mg/kg/day . In another study,
reduced offspring body weights, but no other reproductive
effects, were seen in rats at doses of up to 75 mg/kg/day
. From the data, it appears that prometryn is
unlikely to cause reproductive effects.
- Teratogenic effects: No teratogenic
effects were seen in the offspring of rats fed 250
mg/kg/day, the highest dose tested . In another
study, no teratogenic effects were seen in rats at doses
of 50 mg/kg/day . No teratogenic or developmental
effects were seen in rabbits at doses of 72 mg/kg/day
. Prometryn does not appear to cause birth defects.
- Mutagenic effects: Eleven different
tests for mutagenicity involving hamsters, bacteria, or
mammalian cell cultures have all produced negative
results, indicating that prometryn is not a mutagen .
- Carcinogenic effects: Prometryn was not
carcinogenic in a 2-year rat feeding study at doses of up
to 62.5 mg/kg/day . Carcinogenic effects were not
seen in mice at doses of up to 300 mg/kg/day over 18
months. The available data suggest that prometryn is not
- Organ toxicity: Target organs identified
through animal studies include the liver, kidneys, and
- Fate in humans and animals: The
triazines are generally well-absorbed by the mammalian
gut, and probably across the skin . 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 . No detectable residues of
prometryn or its metabolites were found in the muscle,
fat, blood, liver, kidney, and other organs of sheep and
cattle fed up to 100 ppm for 4 weeks. However, prometryn
or its breakdown products were found in whole milk
samples taken from cows that were fed up to 100 ppm in
their diet for 21 days .
- Effects on birds: Prometryn is
practically nontoxic to birds; the acute oral LD50 values
in bobwhite quail and mallard ducks are greater than 2150
mg/kg and greater than 4640 mg/kg, respectively. The
reported 5- to 7-day dietary LC50 values are greater than
10,000 ppm for these same species .
- Effects on aquatic organisms: Prometryn
is moderately toxic to fish, with reported 96-hour LC50
values of 2.5 to 2.9 mg/L in rainbow trout, 10.0 mg/L in
bluegill sunfish, 3.5 mg/L in goldfish, and 8 mg/L in
carp [15,40,41]. It is highly toxic to guppies . It
is slightly toxic to freshwater invertebrates . A 19%
decrease in shell growth was observed in oysters exposed
to 1.0 mg/L of the herbicide for 48 hours. Pink shrimp
were unaffected by exposure to 1.0 mg/L of the herbicide
for 48-hours . However, the compound has a 48-hour
LC50 in the invertebrate Daphnia of 18.9 mg/L [15,41].
The observed concentration of prometryn in bluegill and
in rainbow trout is 9 to 10 times the ambient water
concentration, indicating a low potential for
- Effects on other organisms: Prometryn is
nontoxic to bees and earthworms, with a reported contact
LD50 of greater than 99 ug/bee, and a 48-hour LC50 of 153
mg/kg in earthworms [6,15].
- Breakdown in soil and groundwater:
Prometryn is moderately persistent in the soil, with a
field half-life of 1 to 3 months . It will persist
longer under dry or cold conditions, which are not
conducive to chemical or biological activity [15,38].
Following multiple annual applications of the herbicide,
prometryn activity can persist for 12 to 18 months after
the last application . Soil microorganisms readily
break down prometryn in the soil [15. The amount of the
herbicide evaporating from soil increases with
temperature and soil moisture content, but volatilization
is not significant under most field conditions [15,38].
Prometryn is weakly bound to most soils, and is slightly
soluble in water . It may thus be mobile in some
soils. However, it adsorbs more strongly to soils with
higher proportions of clay and organic matter . Field
leaching studies indicate that prometryn stays in the top
12 inches of treated soil .
- Breakdown in water: No significant
hydrolysis, or breakdown in water, was found when
prometryn was tested over a period of 28 days in water
ranging from slightly acidic to slightly alkaline and
over a variety of test temperatures . These data
indicate that prometryn is potentially persistent in the
- Breakdown in vegetation: Prometryn is
rapidly absorbed through both the foliage and roots of
plants, and is translocated to the growing shoots .
Removal or degradation by the plant is rapid in
non-susceptible plants, but very slow in susceptible
- Appearance: Prometryn is a colorless,
crystalline solid .
- Chemical Name:
- CAS Number: 7287-19-6
- Molecular Weight: 241.37
- Water Solubility: 48 mg/L @ 20 C 
- Solubility in Other Solvents: s. in
organic solvents, including ethanol, methanol, acetone,
dicloromethane, and toluene 
- Melting Point: 118-120 C 
- Vapor Pressure: 0.13 mPa @ 20 C 
- Partition Coefficient: 3.3404 
- Adsorption Coefficient: 400 
- ADI: Not Available
- MCL: Not Available
- RfD: 0.004 mg/kg/day 
- PEL: Not Available
- HA: Not Available
- TLV: Not Available
P.O. Box 18300
Greensboro, NC 27419-8300
- Phone: 800-334-9481
- Emergency: 800-888-8372
References for the information in this PIP can be found in
Reference List Number 8
information in this profile does not in any way replace or
supersede the information on the pesticide product labeling or
other regulatory requirements. Please refer to the pesticide