on health and environment of glyphosate-containing herbicides
Glyphosate is a systemic herbicide acting in a post- emergence,
non-selective, broad-spectrum manner, and is used to kill undesirable
plants such as annual and perennial grasses, broad -leaved plants and
woody species. Glyphosate, N(-phosphonomethyl) glycine is an acid, but it
is commonly applied as a salt, most often the isopropylamine salt. Its
most common commercial name is Round-up. In Colombia, apart from its use
as an herbicide in agriculture, it is used as a grain dessicant and as a
ripening agent by aerial application and in illicit crop eradication
programs - the subject of this presentation. As a crop eradication agent,
glyphosate will also eradicate foodcrops and forest species, and the true
impacts of its use on health and the environment have not yet been
The worldwide sales of glyphosate, whose main producer is Monsanto, are
presently over $1,500 million annually, this is calculated to increase to
$2,000 million over the next five years, equivalent to more than 40,000
the tons of the active ingredient (Dinham, 1998). At present, sales of
this herbicide makeup about 40 percent of Monsanto’s agrochemical market
worldwide (worldwide sales total $4,3032 million in 1998, 23.2% more than
in 1997). In 1998, Monsanto held second place in the sale of agrochemicals
after Novartis and first-place in the production and sale of transgenic
seeds, genetically modified so that crops that are resistant to glyphosate
-increasing the sales of this agrotoxin (Dinham, 1999).
Between 1986 and 1996 the use of glyphosate tripled in the US. In
Europe its use increased 129% between 1991 and 1995 due to the
declarations by Monsanto that the herbicide is not harmful to human beings
and is environmentally safe. But, according to Cox (1995) and Dinham
(1998), there are data from independent scientific investigations about
glyphosate-containing herbicides, that contradict Monsanto’s statements
and give a very different view of their health and environmental risks.
Before being marketed, herbicides pass through a formulation process,
during which the active ingredients are mixed with other substances such
as solvents, adjuvants etc, known as "inert ingredients," which
are not described on the labels. In many cases, "inert
ingredients" are active biologically, chemically, or are toxic, and
can produce different characteristics when found in the commercial
formulations, than in any of the components alone. This means that if
one doesn’t make careful toxicological studies of the commercial
herbicides, as used in the real world, it becomes impossible to evaluate
their risks to the environment and human health.
The majority of the products that contain glyphosate are made or are
used with a surfactant to aid glyphosate’s penetration into the tissues
of the plant, which bestows different toxicological characteristics to the
commercial formulations in comparison to glyphosate alone. In the case of
Roundup, the herbicidal formulation most used, it contains a surfactant
called polyoxyethylamine (POEA), organic acids related to glyphosate,
isopropylamine, and water. In the present study we will make examine to
the characteristics of glyphosate, but separately the scientific studies
made with Round-up.
In Colombia, Monsanto has registered glyphosate (ICA
1998) under the commercial names Roundup, Rocket, Rocky, Faena, Patrol,
Squadron, Ranger and Fuete. Other agrochemical businesses alsohave
registered commercial formulations based on the same active ingredient,
under the names of: Batalla (Bayer); Glyfoagri (Disagri); Socar (Agrevo);
Crossout, Candela y Glyfosan (Agroser); Glifonox (Crystal); Glifosol (Coljap);
Stelar (Dow); Panzer (Invequímica); Glyphogan (Magan); Faena (Proficol);
Regio (Quimor); Sunup (Sundat); Glifosato Agrogen (Agroquímicos del Cauca)
y Tunda (Fertilizantes Cafeteros).
Mode of Action
The herbicidal action of glyphosate is probably due to the inhibition
of the biosynthesis of aromatic amino acids (phenylalanine, tyrosine, and
tryptophan), used for the synthesis of proteins essential for the growth
and survival of most plants. Glyphosate inhibits the enzyme 5-enolpyruvylshikimate-3-phosphate
synthase, important for the synthesis
of aromatic amino acids; and it may also inhibit or repress the activity
of other enzymes, chlorismate mutase and prephrenate hydratase, both
involved in other steps of the synthesis of those same aminoacids. All of
these enzymes are part of the shikimic acid pathway, present in higher
plants and microorganisms but not in animals.
Glyphosate can affect enzymes not connected with the shikimic acid
pathway. In sugar cane, it lowers the activity of one of the enzymes
involved in sugar metabolism, acid invertase. This reduction appears to be
mediated by auxins (plant hormones).
Glyphosate also affects animal and human enzyme systems. In rats,
injection into the abdomen decreases the activity of two detoxification
enzymes, cytochrome P-450 and a monooxygenase, and decreases the
intestinal activity of the enzyme aryl hydrocarbon hydroxylase (Cox 1995).
New More Toxic Formulations of Glyphosate
Research: According to greenhouse investigations in
Maryland, USA and field investigations between 1995 and 1997 in Hawaii,
with the addition of two surfactants, AL-77 and Optima to the glyphosate
in the Rodeo formulation, the toxicity of glyphosate against coca was
increased by a factor of four, compared to the commercial Roundup formula
(Collins & Helling). According to this study, the herbicide mixture
presently used in Colombia for coca eradication has been
"modified", with excellent results.
This supposed change of formulation coincides with complaints from the
affected communities, who claim that more damage is being done to grasses
and food crops, and that the symptoms of the resultant intoxication are
more serious. We do not know exactly what formulation is being used. The
two new surfactants are made up of the following:
A77: 1:1 mixture (by volume) of Agridex and Silwet L-77.
Agri-Dex: a mixture of heavy-range paraffin-based petroleum oil.
Silwet L-77: polyalkeleneoxide-modified heptamethyltrisiloxane.
Optima: mixture of polyethoxylated alkylamines, alkyl polyexylene
glycols, and organic acids.
Herbicides that contain glyphosate such as Roundup
are registered in Colombia in Toxicity Class IV, slightly toxic, based on
the oral LD50 2 of its active ingredient, considered
to be more than 5,000 mg/kg (earlier it was thought to be 4,320 mg/kg and
within Toxicity Class II). But in the United States these herbicides have
been reclassified by the Environmental Protection Agency (EPA) as Class
II, highly toxic, because of eye irritation 3 (Meister 1995).
The EPA has classified it as "medium" irritant, but the World
Health Organization has found more serious effects; in several studies
using rabbits it was characterized as "strongly" irritating or
"extremely" irritating (Cox 1995). The active ingredient,
Glyphosate on its own, is classified in Category I, extremely toxic.
Both glyphosate alone as well as the products that contain it are more
toxic through dermal application and inhalation than by oral ingestion,
the most common routes of occupational exposure. In several tests, the
inhalation of Roundup in rats caused signs of intoxication in all of the
groups studied and even in the lowest doses applied. Symptoms included a
dark nasal secretion, panting, congested eyes, reduced activity, hair
standing on end, loss of body weight, and blood-congested lungs.
Roundup is one of the most common of the herbicides that cause human
poisoning incidents. It the majority of these have involved eye and skin
irritation in workers, after exposure during mixing, transporting, or
application. Nausea and periods of dizziness have also been reported after
exposure as well as respiratory problems, increased in blood pressure, and
Cases of accidental poisoning or intentional ingestion as well as
occupational exposure of Roundup studied by Japanese doctors and the
following symptoms of acute poisoning were reported: gastrointestinal
pain, massive loss of gastrointestinal liquid, vomiting, excessive fluid
in the lungs, congestion and lung dysfunction, pneumonia, loss of
consciousness, destruction of red blood cells, abnormal
electrocardiograms, low blood pressure, and damaged or reduced hepatic
Many of these symptoms are presently being experienced by Yanacona
Indians living in the Colombian Macizo of the Cauca Department, Colombia,
especially by children, who have received indiscriminate fumigations over
houses and schools, and by people working in their food-crop plots
(additionally, this fumigation is also destroying the forage on which the
animals depend, and potato, corn, onion, ulluco potatoes, coriander and
other crops, upon which these communities survive).
The surfactant in Roundup is considered to be the principal cause of
the toxicity of this formulation. POEA has an acute toxicity of three
times greater than that of Glyphosate, and causes gastrointestinal and
central nervous system damage, respiratory problems, and the distraction
of red blood cells in humans. Furthermore it is contaminated with 1-4
dioxane, which has caused cancer in animals and damage to the liver and
kidneys in humans.
The EPA has found that exposures to residues of Glyphosate in water for
human consumption above the maximum authorized limit of 0.7 mg/l can cause
rapid respiration and lung congestion.
Chronic Toxicity: Glyphosate has also been found to be toxic in
long-term studies in animals. With high doses in rats (900-1200 mg/kg of
body weight per day) decreased body weight in females was reported; an
increased incidence of cataracts and lens degeneration in males; and
increased liver weight in males. At lower doses (400 mg/kg of body weight
per day) inflammation of the stomach's mucous membrane occurred in both
At high doses (about 4800 mg/kg of body weight per day) in rats, males
experienced decreased body weight, excessive growth of particular liver
cells, death of the same liver cells, and chronic inflammation of the
kidney. In females, excessive growth of some kidney cells occurred. At a
lower dose (814 mg/kg of body weight per day) excessive cell division in
the urinary bladder occurred.
According to the EPA, continual exposure to residues in water in
concentrations above 0>7 mg/L can cause liver damage.
Reproductive Effects: In rat and rabbit feeding studies, Glyphosate
affected semen quality and sperm counts (Cox 1995, Dinham 1998). According
to the EPA, continual exposure to residue in water in concentrations
higher than 0.7 mg/L can cause reproductive problems in humans.
Carcinogenicity: The EPA initially classified Glyphosate as a
"Group D Toxin": "not classifiable as a human
carcinogen". Later, in the beginning of the 1990's, they placed it in
"Group C": -"possible human carcinogen". At present,
it is classified as a "Group E Toxin": "No evidence of
carcinogenicity in humans." When this classification was made, it was
added that it was based on the available evidence at that time and should
not be interpreted as a definitive conclusion that the product is not a
carcinogen in every circumstance. This statement is probably due to the
fact that the potential for Glyphosate to cause cancer has been the
subject of a continuing controversy since the beginning of the studies
during the early 1980's.
The first study (1979-1981) showed an increase in testicular
interstitial tumors in male rats at the highest dose tested (30 mg/kg of
body weight per day), as well as an increase in the frequency of a thyroid
cancer in females. The second study (completed in 1983) found dose-related
increases in the frequency of a rare kidney tumor. Another study
(1988-1990) showed an increase in the number of pancreas and liver tumors
in male rats together with an increase of the same thyroid cancer found in
an earlier study in females. None of these increases in tumor incidence
were not considered compound-related by the EPA; or they did not have
statistical significance, that it was not possible to consistently
distinguish between thyroid tumors and cancer, and that there was no
relationship with dose, or that there was no disease progression.
Concerns regarding the potential carcinogenicity of glyphosate persist,
because of the contaminant N-nitroso-glyphosate (NNG) at 0.1 ppm or less,
or this compound can be formed in the environment by simple reaction with
Nitrate (present in human saliva or fertilizers), and it is known that the
majority of N-nitroso compounds are carcinogenic. And there is no safe
dose for carcinogens. Additionally, in the case of Roundup, the surfactant
POEA is contaminated with 1-4 dioxane, which has caused cancer in animals,
and liver and kidney damage in humans. Formaldehyde, another known
carcinogen, is also a breakdown compound of Glyphosate.
Drift: Sublethal doses of glyphosate carried by the wind (drift)
harm wild flowers and may affect some species more than 20 meters from the
site sprayed. Drift is inevitable when applying pesticides, and will
depend on several circumstances, including method of application (ground
or aerial) and wind velocity. The distances measured for the different
methods of application are as follows:
Ground applications: from 14% to 78% of the glyphosate applied leaves
the site. Sensitive species died at 40 meters. The models indicate that
susceptible species may die at 100 meters. Residues have been found 400
meters from the site of ground application.
Helicopter applications: From 41% to 82% of the glyphosate applied by
helicopter moved out of the site.
Applications by plane: Aerial application by plane results in the
greatest drift. In a study in California, glyphosate was found at 800 m,
the greatest distance studied.
In Canada, it has been determined that the buffer zones should be from
75 m to 1,200 m to prevent damage to the vegetation that should be
Soil contamination: The information on the movement and persistence
of glyphosate in the soil is varied. According to the EPA and other
sources, glyphosate that reaches the soil is thoroughly adsorbed, even in
soils low in clays and organic matter. Therefore, though highly soluble in
water, it is considered immobile or almost immobile, remaining in the
upper soil layers, with little propensity for percolation and with a low
potential for runoff, except when adsorbed to colloidal material or
particles suspended in the runoff water.
Several researchers state that glyphosate may be easily leached from
some kinds of soil, i.e. that it may be released from the particles, and
may be very mobile in the soil environment (Dinham, 1998). In a soil, 80%
of the glyphosate was released in a period of two hours (Cox, 1995).
Losses due to volatization or photodecomposition are insignificant, but
it is decomposed by microorganisms; there have been reports of half-lives
in the soil (time that it takes for one-half of a compound to disappear
from the environment) of approximately 60 days (two months), according to
the EPA, and from 1 to 174 days (almost six months) for others.
Nonetheless, the EPA adds that in field studies the residues are often
found the following year.
Some studies speak of lengthy persistence in soil. The initial
degradation is quicker than the later degradation of what remains,
resulting in long persistence. Long persistence has been found in several
studies, resulting in 249 days in agricultural soils and from 259 to 296
days in eight forest sites in Finland; 335 days in a forest site in
Ontario (Canada); 360 days in three forest sites in British Columbia
(Canada); and one to three years in 11 forest sites in Sweden.
It is not easy to detect residues of highly water-soluble substances
like glyphosate, tebuthiuron, and imazapyr in the laboratory, because
laboratory tests commonly work with organic solvents. Hence the importance
of biological tests or the planting of susceptible crops, which may make
it possible to detect the presence of herbicides when residues are no
longer detected in the laboratory.
Contamination of waters: Glyphosate is highly soluble in water,
with solubility of 12 grams/liter at 25EC.
According to the EPA, it may enter aquatic ecosystems by accidental
spraying, by drift, or by surface runoff. Due to its ionic state in water,
it is not expected to be volatile in water or in soil. It is considered to
disappear rapidly in water, as a result of adsorption to particles
in suspension such as organic and mineral particles, to sediments, and
probably due to microbial decomposition.
If it is accepted that glyphosate is easily adsorbed to soil particles,
it will have little potential to move on to contaminate surface waters and
groundwater. But if it is easily absorbed or is easily released from the
soil particles, as mentioned in the previous point, the situation changes.
What is clear is that glyphosate has been found contaminating surface
waters and groundwater. For example, it contaminated two ponds on farm in
Canada due to runoff, one due to an agricultural treatment, the other due
to a spill; it contaminated surface waters in the Netherlands; and seven
wells in the United States (one in Texas and six in Virginia) were found
to be contaminated by glyphosate.
Its persistence in water is shorter than in soil. In Canada it has been
found to persist from 12 to 60 days in soil pond waters, but it persists
longer in the sediments at the bottom. The average life of the sediments
was 120 days in a study done in Missouri, United States. The persistence
was more than one year in sediments in Michigan and Oregon.
In the United Kingdom, since 1993 the Welsh Water Company has detected
levels of glyphosate in waters at levels above those permissible levels
set by the European Union.
Contamination of foods: Analyses of glyphosate residues are
complicated and costly, therefore they are not done routinely by the
government in the United States. Yet there are research studies that show
that glyphosate may be taken by plants and moved to those parts used for
food. For example, glyphosate has been found in strawberries, blueberries,
raspberries, lettuce, carrots, and barley after application.
Its use prior to the wheat harvest to dry the grain results in
"significant residues" in the grain, according to the World
Health Organization; contains residues 2 to 4 times greater than the whole
grain, and they are not lost during baking.
Glyphosate residues have been found in lettuce, carrots, and barley
planted one year after the glyphosate was applied.
Effects on animals
Insects and beneficial arthropods: Glyphosate is toxic to some
beneficial organisms such as parasitic wasps and other arthropod
predators, and soil arthropods that are important for its aeration and in
the formation of humus; and some aquatic insects.
Fish and other aquatic organisms: Different fish species have
different susceptibilities to glyphosate. Acute toxicities in terms of the
CL50 range from 3.2 ppm to 52 ppm, which means moderate
toxicity. Yet Roundup is some 30 times more toxic to fish than glyphosate
alone, i.e. it is from extremely to highly toxic to these aquatic
The factors that influence the toxicity of glyphosate and of products
that contain it include: (a) the species; (b) water quality (glyphosate in
soft water can be 20 times more toxic to rainbow trout than in hard
water); (c) age is also a factor, for example Roundup may be four times
more toxic to young rainbow trout than to older ones; (d) nutrition
affects toxicity, toxicity being greater when the fish are hungry; (e)
toxicity increases with temperature; the effect is greater on aquatic
specifics susceptible to these changes.
Sub-lethal effects on fish may also be significant and occur at low
concentrations in water. For example, in studies with rainbow trout,
concentrations equivalent to one-half and one-third of CL50
caused erratic swimming, and the trout also showed difficulty breathing.
The changes in conduct alter their capacity for feeding, migration, and
reproduction, and they lose the capacity to defend themselves.
Birds: Glyphosate is moderately toxic to birds. In addition to
direct effects, it may have indirect effects because it kills plants,
therefore it may cause dramatic changes in the structure of the plant
community, with a detrimental impact on birds, because they depend on the
plants for food, protection, and nesting. This has been documented in
studies of the populations exposed.
Small mammals: In field studies, populations of small mammals have
also been affected by glyphosate, by death of the vegetation that they or
their prey use for food or protection.
Earthworms: A study in New Zealand showed that glyphosate
significantly affects the development and survival of one of the commonest
worms in its agricultural soils. Applications every 15 days at low doses
(1/20 the normal dose) reduced growth and increased the time for reaching
maturity and mortality.
Effects on desirable plants: Glyphosate, as a broad-spectrum
herbicide, has toxic effects on most plant species. It affects trees and
hedge shrubs and near-by crops, and increases the susceptibility of the
crops to disease. It may pose a risk to endangered species if applied in
areas where they live.
In a study, glyphosate inhibited the formation of nitrogen-fixing nodes
in clover for 120 days after treatment.
Resistant weeds: In 1996, ryegrass resistant to glyphosate was
discovered in Australia.
Gene contamination by transgenic crops: Gene contamination in
significant number of transgenic crops is inevitable. It has been found
that the spread of pollen by the wind in large fields of crops occurs at
much greater distances and in larger concentrations that what is predicted
based on experimental lots. Therefore, the risk of transmitting the
resistance to herbicides introduced by genetic engineering of crops to
similar weeds is real.
Increase in the use of herbicides with Roundup-Ready crops:
Herbicide-resistant crops will intensify and increase the dependency on
herbicide use in agriculture, instead of diminishing it, as the
manufacturers say, by increasing the adverse environmental effects in
soils and water, and repercussions on health.
The development of resistance to glyphosate in weeds by gene flow, or
the practices to minimize the risks of resistance in weeds, will
perpetuate the practice of applying herbicide mixes. There is also a risk
of re-introduction of herbicides to control encroaching crop populations
and glyphosate-resistant weeds.
Increase in the use of insecticides and fungicides: The toxicity of
glyphosate to organisms beneficial to the soil, to beneficial predator
arthropods, and its capacity to increase the susceptibility of the crops
to diseases means that its use leads farmers to step up the use of
insecticides and fungicides.
Failures in the production of Roundup-ready cotton: Roundup Ready
cotton, resistant to glyphosate, was introduced in the United States in
1997. In the first crop, 12,000 hectares failed. One-fourth of 200 farmers
licensed to grow the cotton found deformed capsules xx(other?) and early
loss of capsules.
Collins, Ronald T. And Helling, Charles S. Increased control of
Erythroxylum sp. By glyphosate utilizing various surfactants. DRAFT COPY.
Weed Science Laboratory, USDA-ARS, BARC-W, 10300 Baltimore Ave,
Beltsville, MD USA 1999
Cortina, Germán D. Evaluación del impacto mutagénico
del glifosato en cultivos de linfocitos. Fundación Esawá. Florencia,
Caquetá. 13 p.
Cox, Caroline. Glyphosate, Part 1: Toxicology. En:
Journal of Pesticides Reform, Volume 15, Number 3, Fall 1995. Northwest
Coalition for Alternatives to Pesticides, Eugene, OR. USA. 13 p.
Cox, Caroline. Glyphosate, Part 2: Human exposure and
ecological effects. En: Journal of Pesticides Reform, Volume 15, Number 4,
Winter 1995. Northwest Coalition for Alternatives to Pesticides, Eugene,
OR. USA. 14 p.
Dinham, Barbara. Resistance to glyphosate. En:
Pesticides News 41: 5, September 1998. The Pesticides Trust. PAN-Europe.
Dinham, Barbara. "Life sciences" take over.
En: Pesticides News 44: 7, June 1999. The Pesticides Trust. PAN-Europe.
Instituto Colombiano Agropecuario ICA. División
Insumos Agrícolas. Listado general de plaguicidas registrados hasta
agosto 26 de 1998. Santafé de Bogotá. 21 p.
Meister, Richard. 1995 Farm Chemicals Handbook. Meister
Publishing Company. Willoughby, USA. 922 p.
EPA. Technical Fact Sheets on: Glyphosate. National
Primary Drinking Water Regulations. Document obtained over the Internet,
U.S. Department of Agriculture, Forest Service by
Information Ventures, Inc. Glyphosate, Pesticide Fact Sheets. November
Corrosive: corneal opacity for 7 days.
reversible corneal opacity for 7 days; persistent irritation for
Severe irritation for 72 hours.
Non-corneal opacity; reversible irritation in seven days.
Moderate irritation for 72 hours.
Light irritation for 72 hours.
Table 2: Ecotoxilogical categories
(in the diet)3
Very highly toxic
1 Refleja la dosis suministrada a los
animales de prueba con base en el peso del cuerpo.
2 Concentración en la dieta. No se relaciona con el peso del
cuerpo del animal. Medida de exposición ambiental.
3 Concentración en el agua. No se relaciona con
el peso del cuerpo del animal. Medida de exposición ambiental.
Information Ventures, Inc. under U.S. Forest Service
Contract. November 1995.