GLYPHOSATE FACT SHEET

Greenpeace International, November 1996

Glyphosate is the herbicide to which Monsanto's genetically engineered Roundup Ready soybean and other crops such as oilseed rape (canola), and sugar beet are being genetically modified to resist. This fact sheet describes the basic properties of glyphosate and the issues surrounding glyphosate resistance and weed control.

GLYPHOSATE

Chemically, glyphosate is an organophosphate like many other pesticides, but it does not affect the nervous system as other organophosphates do. It is a broad spectrum, non-selective herbicide which kills all plants, including grasses, broad leaf and woody plants. It is absorbed mainly through the leaves and is transported around the whole plant, killing all parts of it. It acts by inhibiting a biochemical pathway, the shikimic acid pathway. At low levels of application it acts as a growth regulator.

There are three forms of glyphosate used as weed killers:

Common brand names are Roundup, Rodeo, Accord and Vision. Glyphosate is technically extremely difficult to measure in environmental samples. Only a few laboratories have the sophisticated equipment and techniques necessary. This means that data is often lacking on residue levels in food and the environment and existing data may not be reliable.

USE IN WEED CONTROL

Glyphosate product sales are worth $1,200 million a year. In the US, glyphosate was used on about 5-8 million hectares annually in the 1980s. In the UK it was used on over 300,000 hectares in 1994. Because it is broad spectrum in action it is used to control a great variety of annual, biennial, and perennial grasses, sedges, broad leaved weeds and woody shrubs. It is used in fruit orchards, vineyards, conifer plantations and many plantation crops (e.g. coffee, tea, bananas); in pre-crop, post-weed emergence in a wide range of crops (including soybean, cereals, vegetables and cotton); on non-crop areas (e.g. road verges and rights of way); in cereal stubble; forestry; gardening and horticulture. Other uses of salts of glyphosate are in growth regulation in peanuts and in sugarcane to regulate growth and speed fruit ripening.

HUMAN TOXICITY

Because the shikimic acid pathway does not exist in animals, the acute toxicity of glyphosate is very low. Glyphosate can interfere with some enzyme functions in animals but symptoms of poisoning are only seen at very high doses. However, products containing glyphosate also contain other compounds which can be toxic. In particular most contain surfactants known as polyoxyethyleneamines (POEA).

Some of these are much more toxic that glyphosate. These account for problems associated with worker exposure. They are serious irritants of the respiratory tract, eyes and skin and are contaminated with dioxane (not dioxin) which is a suspected carcinogen. Some are toxic to fish. Glyphosate is the most frequent cause of complaints to the UK's Health and Safety Executive's Pesticides Incident Appraisal Panel. In California glyphosate is the third most commonly-reported cause of pesticide related illness among agricultural workers. New formulations with surfactants which are less irritant have been developed by Monsanto (e.g. Roundup Biactive), but cheaper, older preparations are still available.

ENVIRONMENTAL TOXICITY

Glyphosate is one of the most toxic herbicides with many species of wild plants being damaged or killed by applications of less than 10 micrograms per plant. Glyphosate can be more damaging to wild flora than many other herbicides as arial spraying with glyphosate can give average drifts of 400 to 800 metres and ground spraying with glyphosate may cause damage to sensitive plants up to 100 metres from the field sprayed.

Glyphosate use is thought to affect hedgerow trees causing die-back and may reduce trees' winter hardiness and resistance to fungal disease. The direct toxicity of glyphosate to mammals and birds is low. However, its effect on flora can have a damaging effect on mammals and birds through habitat destruction. The US EPA concluded that many endangered species of plants as well as the Houston toad may be at risk from glyphosate use. Fish and invertebrates are more sensitive to formulations of glyphosate. As with humans, the surfactants are responsible for much of the harm.

Toxicity is also dependent on water temperatures and pH levels. In Australia guidelines state that most formulations of glyphosate should not be used in or near water because of their toxic effects on tadpoles and adult frogs. The newer, non-irritant formulations such as Roundup Biactive are not included in this advice. Of nine herbicides tested for their toxicity to soil microorganisms, glyphosate was found to be the second most toxic to a range of bacteria, fungi, actinomycetes and yeasts. However, when glyphosate comes into contact with the soil it rapidly binds to soil particles and is inactivated. Unbound glyphosate is degraded by bacteria. Low activity because of binding to soil particles suggests that glyphosate's effects on soil flora will be limited. However, some recent work shows that glyphosate can be readily released from certain types of soil particles, and therefore may leach into water or be taken up by plants.

IMPACT OF GENETICALLY ENGINEERED HERBICIDE RESISTANT CROPS

The introduction of crops engineered to be resistant to glyphosate could have two particularly damaging effects. Firstly, it will increase the use of the herbicide and secondly, it may encourage the emergence of herbicide resistant weeds. Monsanto claim that the introduction of herbicide resistant crops will reduce the overall amount of herbicide used. They argue that glyphosate will replace other, more environmentally damaging herbicides, because only glyphosate need be used rather than several different compounds. They also argue that weed killer will be used less frequently on resistant crops. Importantly they also consider glyphosate to be 'environmentally friendly' and a 'safe' herbicide mainly relying on its inactivation through binding to soil particles and low toxicity to humans to support this claim.

Other herbicides used in soybean and other crops are unquestionably harmful to the environment and human health. The question is whether glyphosate is really any less harmful and whether herbicide resistant plants will reduce the amount of potentially damaging chemical to the environment. Evaluating overall amount of use on a weight or volume basis does not allow for the differences in toxicity between chemicals. Weight or volume of total herbicide may decrease simply because glyphosate is more effective at killing plants than many other chemicals. Glyphosate is already the eleventh most widely used pesticide in the US on a volume basis. Its damaging impacts on the environment have already been described.

Whether there will be a reduction in the number of times herbicide is used is also questionable. In their documents prepared for the US authorities, Monsanto say that under current regimes, between one and five applications of different herbicides or herbicide mixtures are needed to control weeds in soybean crops and that with Roundup Ready soybean only 'one or possibly two' applications of Roundup will be needed. Yet in their information for farmers in Argentina, Monsanto recommend Roundup is used with Roundup Ready soybean before sowing, when the young plant has three to four leaves and then whenever the farmers find weeds. This is 'at least twice and probably more frequently'.

One of the major concerns of weed scientists is that the emergence of herbicide resistant weeds may be encouraged by the use of herbicide resistant plants. Herbicide resistance arises in an analogous fashion to the emergence of antibiotic resistance in bacteria. Mutations occur in plants and when one arises which makes it resistant to the herbicide, it will have an advantage and grow and flourish when other plants are killed Resistance to glyphosate is easy to induce in plants in the laboratory. Monsanto claim resistance to glyphosate is unlikely to emerge in the field because it does not persist in soil. However, weed resistance to paraquat, another herbicide which has a shorter soil persistence than glyphosate, is already a serious problem. One weed specialist concluded by comparison to paraquat that 'Presumably glyphosate resistance can also be obtained with multi-annual treatments' (Gressel, in Cassley et al, 1991).

Roundup Ready soybean is intended to be used with 'multi-annual treatments' and so the emergence of resistance will be encouraged. Even without the increased use of glyphosate expected with the introduction of resistant crops, recently there has been the first report of glyphosate resistance in a weed which occurred in ryegrass in Australia.

Glyphosate resistant weeds could also arise if there is gene flow between the soybean and a related wild plant or if the soybean survives to emerge as a weed ('a volunteer') in the subsequent crop. Gene flow is possible in the Far East where soybean originated and wild related plants exist. Herbicide resistant volunteers may be a problem where mild climates occur and overwintering of soybean is possible. Herbicide resistant crops are an expensive problem for farmers. Having weeds resistant to another herbicide, triazine, has been estimated to cost farmers up to $25 a hectare in extra weed control expenditure. There would be an extra penalty for farmers growing glyphosate resistant crops if glyphosate resistant weeds evolved, because not only would they have to change their weed control practices but they would have paid a premium for the herbicide resistant seed in the first place.

Thus herbicide resistant soybean promises increased herbicide use and associated damage to the environment together with an increased risk of weed resistance which would be a costly problem for farmers.

References:

*Active Ingredient Fact Sheet: Glyphosate, Pesticide News 33 pp28-29, September 1996;
*Breeze, V, Thomas, G & Butler, R (1992): Use of a model and toxicity data to predict risks to some wild plant species from drift of four herbicides, Annals of Allied Biology 121: 669-677;
*Carlisle S.M. & Trevors, J.T. (1988) Glyphosate in the environment. Water Soil and Air Pollution 39: 409-420;
*Casley J C., Cussans G W & Atkin R K (eds) (1991) Herbicide resistance in weeds and crops, Oxford: Butterworth-Heinmann;
*Marrs R H, Williams, C T, Frost, A J & Plant, R A (1989) Assessment of the effects of herbicide spray drift on a range of plants of conservation interest. Environmental Pollution 59: 71- 86;
*New Scientist, 6 July 1996, p6; Petition for determination of nonregulated status of soybeans with a Roundup Ready gene, Agricultural Group of Monsanto to APHIS, USDA, 1993;
*US-EPA RED Facts: Glyphosate, September 1993;
*Yates W E., Akesson N B & Bayer D E (1978) Drift of glyphosate sprays applied with arial and ground equipment, Weed Science 26 (6): 597-604.

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