Extension Toxicology Network
A Pesticide Information Project of Cooperative Extension Offices
of Cornell University, The University of California, Michigan
State University, and Oregon State University
Extoxnet is a collaborative educational project intended to
convey pesticide-related information in easily understood terms.
Information is provided in two types of documents: Pesticide
Information Profiles (PIPs) on the health and environmental
effects of specific pesticides, and Toxicology Information Briefs
(TIBs), short descriptions of a variety of issues that pertain to
pesticides, such as carcinogenicity, ecological effects, and
epidemiology. The TIBs are intended to assist in the
understanding and interpretation of information in the PIPs.
Data presented through EXTOXNET documents are not based on an
exhaustive literature search.
E X T O X N E T
Extension Toxicology Network
Source: Oregon State University
A broad-spectrum, non-selective systemic herbicide which is highly
active on essentially all annual and perennial plants. Glyphosate is
usually formulated as an isopropylamine salt. While glyphosate can be
described as an organophosphorus compound, it is not an organophosphate
ester but a phosphanoglycine, and does not inhibit acetylcholinesterase
The toxicity of the technical product (glyphosate) and the
formulated product ([7mRoundup[m) is reported as almost the same value, even
though the formulated product is only 41% glyphosate. This is unusual.
For instance, one study of rat oral LD50s showed 4300 to 5600 mg/kg for
the technical material, 5400 mg/kg for [7mRoundup[m and greater than 4900
mg/kg for isopropylamine salt. Other oral LD50s for the technical
material were 1538 to greater than 10,000 mg/kg for mice, rabbits 3500
mg/kg, and goats 3530 to 5400 mg/kg (1,5).
The dermal LD50 for [7mRoundup[m to rats is greater than 17,600 mg/kg
and greater than 5000 in rabbits. In 50 human volunteers, patch tests
produced no visible skin changes or sensitization. Inhalation LC50 for
rats after a four-hour exposure was 3200 mg/cubic meter; there was no
response at 1600 mg/cubic meter(1,5).
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 or
cellular changes. Rats on levels greater than 5000 ppm for 90 days had
some lung weight differences which were of uncertain significance in the
absence of adverse cellular finding in the lungs of the animals(5). Mice
on diets of 50,000 ppm for 90 days had reduced body weight gains and
lifetime administration of 300,000 ppm (5400 mg/kg/day) produced a
slight reduction of body weight and equivocal, microscopic liver and
kidney changes. Blood chemistry and cellular components, and organ
function were not effected.
Neurotoxicity tests with hens fed 7.5 g/kg over three days and
repeated 21 days later produced no effects. There was no microscopic
evidence of nerve damage.
Two three-generation studies on rats have been performed. In the
first study there was some reduction of fertility at the 300 ppm
level(4). However this could not be reproduced in the second study and a
NOEL of 10 mg/kg/day was established for reproductive effects. Wild deer
mice suffered no apparent reproductive effects when a coniferous forest
was sprayed at 2 lbs/acre(4).
Rabbits receiving 30 mg/kg/day by stomach tube on days 6 through 15
of gestation had offspring with fetotoxic or teratogenic effects. At
doses of 350 mg/kg/day on days 6 through 27, the dams suffered numerous
toxic effects and some death, but no teratogenic effects were noted in
Rats given doses up to 3500 mg/kg on days 6 to 19 of gestation had
offspring with no teratogenic effects but there were maternal and
fetotoxic effects. No fetotoxic effects occurred at 1000 mg/kg/day.
Dominant lethal, host-mediated, or rec-assay tests were negative,
as were tests in seven bacterial and one yeast systems. In human
lymphocytes, the formulated product may be weakly active(5).
Rats and dogs fed 300 ppm in their diets for two years had no
increase in occurrence, type, or number of benign or malignant tumors.
Rats showed some increase in microscopic lipid droplets in the liver(5).
This effect was not seen in a later study at levels up to 600 ppm(4).
Mice on diets containing up to 3% glyphosate (5400 mg/kg/day) had
reduced body weights and equivocal liver and kidney changes but no
carcinogenic effects. Blood samples were taken periodically and a series
of functions evaluated. All tissues and organs were examined for cancer
upon death or sacrifice.
A disputed study where glyphosate was administrated into the
stomach cavity of rats at doses up to 60 mg/kg for 28 days showed weight
gain effects and blood effects. These are effects similar to those
caused by materials which alter mitochondrial energy transformation(1).
Fate in Humans and Animals:
Glyphosate is poorly absorbed from the digestive tract and is
excreted unchanged by mammals. Rats excreted 99% and rabbits excreted
about 90% of a single oral dose in 120 hours. Ten days after treatment
there was 0.1 ppm or less in the tissues of rats fed 100 ppm for 19
days. No single tissue showed accumulated(3).
Cows, chickens, and pigs fed up to 75 ppm 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).
Mallards and bobwhite quail both had an LC50 of greater than 4640
ppm. Hatchability or time to hatch of domestic chicken eggs dipped in a
solution of 5% had no effect. The bioaccumulation factor in chicken
muscle, fat, eggs, and liver was as low as 1/10,000 of the environmental
In fish the formulated product, [7mRoundup[m, was more toxic than
glyphosate. In rainbow trout, for instance, the 96-hour LC50 was 8.3 ppm
with [7mRoundup[m and 38 ppm with glyphosate. For bluegill the 96-hour LC50
was 5 ppm, 78 ppm for glyphosate. The surfactant used in the [7mRoundup[m
formulation (a modified tallow amine) is apparently somewhat more toxic
to fish than many common surfactants. For this reason, the formulation
for use in aquatic situations (Rodeo) omits the surfactant. There is a
bioconcentration factor of 0.1 to 0.3 (fish/water).
Bees have both an oral and dermal LD50 of greater than 100 ug/per
Glyphosate is highly adsorbed on most soils especially those with
high organic content. One study showed 7% of the applied material in the
leachate from 30 centimeter columns. Microbial action is responsible for
degradation with a half-life of 3 to 130 days. The primary metabolite
aminomethyl phosphonic acid (AMPA), degrades somewhat slower than the
Glyphosate is strongly adsorbed to both organic and mineral matter
and is degraded primarily by microorganisms in water to AMPA. Half-lives
in ponds range from 12 days to 10 weeks. Because glyphosate is so
tightly bound to the soil, not much is picked up by rain or irrigation
water. One estimate had 1.85% of the applied chemical lost to runoff(4).
Photodecomposition plays a minor role in environmental breakdown.
The prime mode of action in plants is on the shikimic acid pathway.
It appears that 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 the roots. The
half-time in forest vegetation is less than four weeks.
Monsanto Company Telephone: 314/694-1000
800 N Lindbergh Blvd
St Louis, MO 63167 Emergency: 314/694-4000
Common name glyphosate
CAS # 1071-83-6 N-(phosphonomethyl)glycine
Chemical class/use phosphanoglycine compound/herbicide
Solubility in water 10,000 ppm
Solubility in solvent 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 at 20 ppm
0.6 X 10 to the minus 3 at 100 ppm
rat 10 mg/kg (ppm); renal; three generation
HA 700 ug/l (ppb) (lifetime)
ADI 0.03 mg/kg (ppm) (EPA)
0.3 mg/kg (ppm) (WHO)
1. National Library of Medicine (1987). Hazardous Substances Databank.
TOXNET, Medlars Management Section, Bethesda, MD.
2. Grossbard, E. and D. Atkinson, Editors (1985). The Herbicide
Glyphosate, Butterworths, Boston, MA.
3. U. S. Environmental Protection Agency (1987). Health Advisory, Office
of Drinking Water.
4. Forest Service, (1984). Pesticide Background Statements, Vol. I
Herbicides. United States Dept.of Agriculture, Agriculture Handbook
5. Monsanto Company (1985). Toxicology of Glyphosate and [7mRoundup[m
Herbicide, Department of Medicine and Environmental Health, St.
DISCLAIMER: The information in this profile does not in any way replace
or supersede the information on the pesticide product label/ing or other
regulatory requirements. Please refer to the pesticide product
Gabriel A. Hegyes
Sustainable Agriculture Network
On Wed, 6 Jul 1994 KATYemail@example.com wrote:
> If this request does not follow proper netiquette, please let me
> know: Does anyone have any information as to whether or not
> Round-Up breaks down in water? Thanks very much :)