E X T O X N E T
Extension Toxicology Network
A Pesticide Information Project of Cooperative Extension Offices of
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University of California at Davis. Major support and funding was provided
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Pesticide
Information
Profile
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Primisulfuron-methyl
Publication Date: 5/94
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TRADE OR OTHER NAMES
Trade names for the compound include Beacon, CGA-136872 and Rifle.
Primisulfuron-methyl may be found in other herbicide formulations such as
2,4-D, dicamba, cyanazine, bromoxynil and atrazine.
REGULATORY STATUS
Primisulfuron-methyl is a General Use Pesticide (GUP).
INTRODUCTION
Primisulfuron-methyl is a urea herbicide that is used on crop and non-
crop areas for the control of grass weeds and many kinds of broad-leaved
weeds. The compound is a selective postemergence systemic herbicide that
is rapidly absorbed by plants and transported throughout the plant roots
and foliage. The herbicide works by blocking cell growth in the active
growing regions of the plant. The herbicide also acts to inhibit
photosynthesis (1, 4).
TOXICOLOGICAL EFFECTS
ACUTE TOXICITY
Primisulfuron-methyl is a slightly toxic compound and requires that
the signal word CAUTION be used on the label. The acute oral LD50 for
primisulfuron-methyl is greater than 5,050 mg/kg in the rat and the LD50
for skin toxicity is greater than 2,010 mg/kg (1, 2). Both of these values
indicate that there is little acute toxic threat from exposure or contact
with the herbicide. In addition there is little skin irritation from
primisulfuron-methyl and it is not a skin sensitizer (4). In rabbits,
primisulfuron-methyl caused slight eye irritation that cleared within three
days after contact (2). The four hour inhalation LC50 of primisulfuron-
methyl was greater than 4.8 mg/l for rats (1).
The trade product Beacon, which contains 75% of this active
ingredient, is classified as slightly toxic for skin, inhalation and eye
exposure. It is not a skin sensitizer (1).
CHRONIC TOXICITY
Rats and mice fed very large amounts of primisulfuron-methyl for up to
ninety days showed no ill effects (2). This indicates that even at
relatively high levels of exposure (500 mg/kg) there is little toxic effect
from the compound over relatively short exposure periods. Male rats fed
higher doses of primisulfuron-methyl (up to 1,000 mg/kg) for three months
showed a decrease in body weight and a decrease in spleen weight. The
lowest dose at which adverse effects were noted (LEL) was about 150 mg/kg
(2). When dogs were fed moderate doses of primisulfuron-methyl for a year,
a number of effects were noted at the highest doses tested (125 mg/kg)
which include changes in the blood such as increased platelets and anemia.
Other changes include decreased cholesterol, pale livers, and thyroid gland
changes.
This evidence suggests that the chronic risks of human exposure to
moderate levels of the herbicide for extended periods of time are slight.
Reproductive Effects
In a two generation study, rats were fed moderate doses (250 mg/kg) of
primisulfuron-methyl. Rats had decreased testicular function and the
offspring had decreased body weights. No compound related reproductive
effects were noted at doses below 50 mg/kg/day (1).
In a two year dietary study, rats were fed high doses (500 mg/kg) of
primisulfuron-methyl. The rats, at the end of the study, had soft and
atrophied testes (1). Further study is necessary to fully assess the
potential reproductive toxicity of the compound, although it does not
appear that such toxicity would occur during normal use.
Teratogenic Effects
Pregnant rabbits fed high doses of primisulfuron-methyl produced
normal offspring. Only at doses of 300 mg/kg and above were there changes
in maternal body weight, spontaneous abortion and changes in the maternal
stool. In another study, pregnant rats were fed moderate doses of
primisulfuron-methyl. They showed increases in the number of litters
having incomplete bone formations, though this study was inconclusive.
The EPA has indicated that it is unlikely, given the results of the
three studies noted above, that primisulfuron-methyl is teratogenic to
humans (1).
Mutagenic Effects
Primisulfuron-methyl did not cause mutations in various tests on
bacteria, hamster cells, rat liver cells and human cells. This indicates
that, at the doses tested, the compound is not mutagenic (1).
Carcinogenic Effects
Two different tests have been conducted to assess the carcinogenicity
of primisulfuron-methyl. The first study lasted for two years with a high
dose of 500 mg/kg. While there were some adverse effects, atrophied testes
and decreased food consumption, no evidence of cancer was found.
In another study, mice were fed up to 1,200 mg/kg/day for a year and a
half. Liver tumors in the mice were observed. However, these tumors and
other adverse effects were present at doses exceeding the maximum tolerated
dose and when mortality occurred (1).
The EPA's Agency Peer Review Committee has determined that
primisulfuron-methyl is not classifiable as a human carcinogen.
Organ Toxicity
Several adverse effects have been noted in the organs of rats and mice
which were fed large doses of primisulfuron-methyl. The most notable were
changes in liver and spleen weights and in the testes of rats (1).
Fate in Humans and Animals
In a rat study, nearly 97% of the primisulfuron-methyl was excreted in
the feces and the urine within 9 days. Most of the parent compound was
unchanged, indicating little metabolic activity. However, there were small
concentrations of five different breakdown products in the urine and feces.
Similar patterns of breakdown were noted in the goat and the chicken (1).
ECOLOGICAL EFFECTS
Effects on Birds
Primisulfuron-methyl is practically non-toxic to wildfowl. Both
bobwhite quail and mallard ducks show a high tolerance for the compound.
The LD50 for primisulfuron-methyl in both species was in excess of 2,150
mg/kg. In addition, mallards fed moderate amounts of the compound showed
no adverse reproductive effects at the highest dose tested, 500 ppm (1).
Effects on Aquatic Organisms
Primisulfuron-methyl is slightly toxic to freshwater fish, aquatic
organisms and to marine (estuarine) shrimp. The LC50 is greater than 48
mg/l in the bluegill and greater than 13 mg/l in the rainbow trout (1).
The compound is practically non-toxic to the freshwater invertebrate
Daphnia magna (2).
Primisulfuron-methyl is unlikely to pose a threat to endangered
aquatic organisms.
Effects on Other Organisms (Nontarget species)
Primisulfuron-methyl is non-toxic to honey bees (4).
ENVIRONMENTAL FATE
Breakdown of Chemical in Soil and Groundwater
In laboratory tests on well aerated soils, half of the initial amount
of the compound was broken down within two months. In soils without oxygen,
breakdown of the compounds took nearly three months (2). Sunlight has
little effect on the breakdown of the compound in soil or in water.
Dissipation of the compound under field conditions was much quicker, with a
half-life of three to twelve days (2).
Primisulfuron-methyl is very mobile in soil in field and laboratory
studies. However, in the field studies, no primisulfuron-methyl was
detected below a depth of 9 inches. The mobility of the compound in soils
indicates that it has the potential to leach to surface water and to
groundwater that lies close to the surface and is in highly vulnerable
soils (1).
Breakdown of Chemical in Surface Water
The breakdown of the compound is much quicker in acidic soils and
water rather than in neutral or alkaline soils and water (1).
Breakdown in Vegetation
Primisulfuron-methyl has been detected at concentrations up to 0.011
ppm in the non-edible portion of untreated food crops such as wheat,
soybeans, sugar beets, corn and lettuce. These crops accumulated the
compound from the site in which corn plants were treated with
primisulfuron-methyl three to twelve months prior to the untreated crops.
Thus, while degradation may be rapid, there is the potential for some
compound residues to remain in the soil (1).
PHYSICAL PROPERTIES AND GUIDELINES
Exposure Guidelines:
| RfD: | NA |
| HA: | NA |
| ADI: | NA |
| PEL: | NA |
Physical Properties:
| CAS #: | 86209-51-0 |
| Chemical name: | 2-[4,6-bis(difluoromethoxy)pyrimidin-2-ylcarbamoylsulfamoyl] benzoic acid |
| Molecular weight: | 468.3 g/mol |
| Solubility in water: | 70 mg/l at 20 degrees C and pH 7. |
| Solubility in solvents: | Acetone, 36 g/l; cyclohexanone, 27 g/l; isopropanol 0.4 g/l; methanol, 3.5 g/l; xylene, 0.3 g/l; toluene, 0.5 g/l. |
| Melting point: | 203.1 degrees C |
| Vapor pressure: | < 1 nPa at 20 degrees C |
| Partition coefficient (octanol/water) (log): | 0.2 |
| Adsorption coefficient: | NA |
| Chemical Class/use: | urea herbicide |
BASIC MANUFACTURER
Ciba-Geigy
Ciba Plant Protection
P.O. Box 18300
Greensboro, NC 27419-8300
FAX: (910) 299-8318
Telephone: (910) 632-6000
Review by Basic Manufacturer:
Comments solicited: April, 1993
Comments received: January, 1994
REFERENCES
Walker, M.M. and L.H. Keith. (1991). EPA's Pesticide Fact Sheet
Database. Lewis Publishers. Chelsea, MI.
The Agrochemical Handbook: Third Edition. (1991). Royal Society of
Chemistry, Unwin Brothers Ltd., Surrey, England.
The Farm Chemicals Handbook. (1992). Meister Publishing. Willoughby,
OH.
Worthing, C.R. and R.J. Hance. (1988). The Pesticide Manual, A World
Compendium. Ninth Edition. The British Crop Protection Council
Disclaimer: Please read
the pesticide label prior to use. The information contained at this web
site is not a substitute for a pesticide label. Trade names used herein
are for convenience only; no endorsement of products is intended, nor is
criticism of unnamed products implied. Most of this information is historical
in nature and may no longer be applicable.
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