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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Glyphosate
Publication Date: 5/94
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TRADE OR OTHER NAMES
Trade names for products containing glyphosate include Roundup,
Rodeo, and Pondmaster. It may be used in formulations with other
herbicides.
INTRODUCTION
Glyphosate is a broad-spectrum, non-selective systemic herbicide
It is useful on essentially all annual and perennial plants including
grasses, sedges, broad-leaved weeds and woody plants. It can be used on
non-cropland and among a great variety of crops.
Glyphosate is usually formulated as an isopropylamine salt. While
it can be described as an organophosphorus compound, glyphosate is not
an organophosphate ester but a phosphanoglycine, and it does not inhibit
cholinesterase activity.
Glyphosate is a general use pesticide.
TOXICOLOGICAL EFFECTS
Acute Toxicity
Glyphosate is a moderately toxic herbicide and carries the signal
word WARNING on the label. Even though the LD50 values show the compound
to be relatively non-toxic it can cause significant eye irritation. The
toxicity of the technical product (glyphosate) and the formulated
product (Roundup) is nearly the same. The acute oral LD50 in the rat is
5,600 mg/kg. Other oral LD50 values for glyphosate are 1,538 to greater
than 10,000 mg/kg for mice, rabbits mg/kg, and goats (1, 5).
In a number of human volunteers, patch tests produced no visible
skin changes or sensitization.
Chronic Toxicity
Subchronic and chronic tests with glyphosate have been conducted
with rats, dogs, mice, and rabbits in studies lasting from 21 days to
two years. With few exceptions there were no treatment-related gross
(easily observable) or cellular changes (5). In a chronic feeding study
with rats, no toxic effects were observed in rats given doses as high as
31 mg/kg/day, the highest dose tested. No toxic effects were observed
in a chronic feeding study with dogs fed up to 500 mg/kg/day, the
highest dose tested (8). Mice fed glyphosate for 90 days exhibited
reduced body weight gains. The lifetime administration of very high
amounts of glyphosate produced only a slight reduction of body weight
and some microscopic liver and kidney changes. Blood chemistry,
cellular components, and organ function were not affected even at the
highest doses.
Hens fed massive amounts over three days and again 21 days later
showed no nerve related effects.
Reproductive Effects
Most of the field and laboratory evidence shows that glyphosate
produces no reproductive changes in test animals. It is unlikely that
the compound would produce any reproductive effects in humans.
Teratogenic Effects
In a teratology study with rabbits, the maternal NOEL was 175
mg/kg/day and no developmental toxicity was observed in the fetuses at
the highest dose tested (350 mg/kg/day) (8).
Rats given doses up to 3,500 mg/kg on days 6 to 19 of pregnancy had
offspring with no teratogenic effects, but other toxic effects were
observed in both the mothers and the fetuses. No toxic effects to the
fetuses occurred at 1,000 mg/kg/day.
Mutagenic Effects
The compound does not cause mutations in microbes. The tests on
eight different kinds of bacterial strains and on yeast cells were all
negative. The compound poses little mutagenic risk to humans (6).
Carcinogenic Effects
Rats and dogs and mice fed glyphosate over a wide range of doses
showed no cancer related effects directly due to the compound (4). EPA
has stated that there is sufficient evidence to conclude that glyphosate
is not carcinogenic in humans (8).
Organ Toxicity
Glyphosate caused no changes in the rate of body weight gain, in
blood, nor in kidneys or liver. The studies were conducted at doses up
to 500 mg/kg (3).
Fate in Humans and Animals
Glyphosate is poorly absorbed from the digestive tract and is
largely excreted unchanged by mammals. Ten days after treatment there
were only minute amounts in the tissues of rats fed glyphosate for three
weeks (3).
Cows, chickens, and pigs fed small amounts had undetectable levels
(less than 0.05 ppm) in muscle tissue and fat. Levels in milk and eggs
were also undetectable (less than 0.025 ppm). Nearly all glyphosate
residues were rapidly eliminated by fish that had been exposed for 10 to
14 days once these fish were transferred to glyphosate-free water.
Glyphosate has no significant potential to accumulate in animal tissue
(9).
ECOLOGICAL EFFECTS
Glyphosate is only slightly toxic to wild birds. The LC50 in both
mallards and bobwhite quail is greater than 4,500 ppm. The
bioaccumulation factor in chicken muscle, fat, eggs, and liver was as
low as 1/10,000 (4).
Glyphosate is practically non-toxic to fish. However, Roundup was
more toxic to fish than was glyphosate. In rainbow trout, for instance,
the 96-hour LC50 was 8.3 mg/l with Roundup and 38 ppm with glyphosate.
The LC50 for glyphosate was 120 mg/l for bluegill sunfish. An additive
used in the Roundup formulation (modified tallow amine used as a
surfactant) is apparently more toxic to fish than many common
surfactants. For this reason, the formulation for use in aquatic
situations (Rodeo) omits this ingredient. The surfactant is used to
allow the compound to readily dissolve in solution and to keep the
compound from balling up on the leaf surface.
There is a very low potential for the compound to build up in the
tissues of aquatic invertebrates or other aquatic organisms. Glyphosate
is relatively non-toxic to honeybees. Its oral and dermal LD50 is
greater than 0.1 mg/ bee (7).
ENVIRONMENTAL FATE
Glyphosate is highly adsorbed on most soils especially those with
high organic content. The compound is so strongly attracted to the soil
that little is expected to leach from the applied area. Microbes are
primarily responsible for the breakdown of the product. The time it
takes for half of the product to break down ranges from 1 to 174 days.
Because glyphosate is so tightly bound to the soil, little is
transferred by rain or irrigation water. One estimate showed less than
two percent of the applied chemical lost to runoff (4). The herbicide
could move when attached to soil particles in erosion run-off.
Photodecomposition plays only a minor role in environmental breakdown.
In water, glyphosate is strongly adsorbed to suspended organic and
mineral matter and is broken down primarily by microorganisms also. Its
half-life in pond water ranges from 12 days to 10 weeks.
Glyphosate may be extensively metabolized by some plants while
remaining intact in others (2). Once in the plant tissue, the chemical
is translocated throughout the plant, including to the roots.
Exposure Guidelines:
| NOEL (rabbit): | 175 mg/kg/day |
| HA: | 0.7 mg/l (lifetime) |
| ADI: | 0.03 mg/kg (EPA)
0.3 mg/kg (WHO) |
| LEL: | 300 mg/kg/day (rabbit) |
Physical Properties:
| CAS #: | 1071-83-6 |
| Chemical name: | N-(phosphonomethyl) glycine |
| Chemical class/use: | Phosphanoglycine herbicide |
| Solubility in water: | 900,000 mg/l |
| Solubility in other solvents: | insoluble in common organics |
| Melting Point: | 200 degrees C |
| Vapor Pressure: | negligible (Monsanto) |
| Dissociation values: | 2.27 (pKa) |
| Partition Coefficient: | 0.17 x 10 to the minus 2 power at 20 ppm; 0.6 x 10 to the minus 3 power at 100 ppm |
BASIC MANUFACTURER
Monsanto Company
800 N. Lindbergh Blvd.
St. Louis, MO 63167
Telephone: 314/694-1000
Emergency: 314/694-4000
Review by Basic Manufacturer:
Comments solicited: November, 1992
Comments received: November, 1992
REFERENCES
National Library of Medicine (1992). Hazardous Substances
Databank. TOXNET, Medlars Management Section, Bethesda, MD.
Grossbard, E. and D. Atkinson, Editors (1985). The Herbicide
Glyphosate, Butterworths, Boston, MA.
U.S. Environmental Protection Agency (1987). Health Advisory,
Office of Drinking Water.
Forest Service (1984). Pesticide Background Statements, Vol. I
Herbicides. United States Dept. of Agriculture, Agriculture Handbook
No. 633.
Monsanto Company (1985). Toxicology of Glyphosate and Roundup
Herbicide, Department of Medicine and Environmental Health, St. Louis,
MO.
Stevens, James T. and Darrell D. Sumner. 1991. Herbicides in
Handbook of Pesticide Toxicology Volume 3, Cases of Pesticides. Wayland
J. Hayes and Edward R. Law editors. Academic Press, NY.
The Agrochemicals handbook. 1991. The Royal Society of Chemistry,
Cambridge, England.
U.S. Environmental Protection Agency (1992). Pesticide Tolerance
for Glyphosate. Federal Register 57 (49): 8739-40.
Malik, J., G. Barry and G. Kishore. 1989. Minireview: The
herbicide glyphosate. BioFactors 2 (1): 17-25.
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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