The glyphosate (N (phosphonométhyl) glycine, C₃H₈NO₅P) is total weeding , i.e. a not-selective Herbicide, formerly produced under patent, exclusively by the company Monsanto as from 1974, under the mark Roundup. The Patent having fallen into the public domain in 2000, other companies produce from now on glyphosate. The glyphosate alone is not very effective, because it does not adhere to the sheets nor does not penetrate them easily. One thus associates a Surfactant to him which is suspected of being the cause of toxicity of the Weeding S containing of the glyphosate.

Some species of plants started to develop resistances to the glyphosate.

Chemical properties

The glyphosate is a weak Acide organic, analog of an Amino-acid natural, the glycine, equipped with a grouping Phosphonate.
Son name is the contraction of glycine, phospho- and - ate. Of this structure.
It presents 4 PKa (0,7; 2,2; 5,9; 10,6). ic Zwitterion whatever the pH, it is also very water soluble and very polar (LogP < -3,2). In the grounds, it is rather quickly adsorbed, and this adsorption (more or less important according to the pH) makes it normally rather not very mobile.
Son principal product breakdown is the AMPA or acid aminomethylphosphonic, resulting from the loss of the group Acétate.

To increase its Solubility and its passage in the plant and the Sap, the industrialists often prepare it in the form of salt of Isopropylamine (C6H17N2O5P, Roundup ). Addititfs (surface-active, such as the Polyoxyéthylène amine) are added to him to fix it on the plants.

Presence in the Environment

In the grounds

The rates of glyphosate are difficult there to measure because of the fact that it is absorbed on the particles of the ground and difficult to extract without denaturing it. It is probably often present there, because it is the weeding first and the first pesticide sold with the world, with a quantity which more than doubled in 4 years, passing from 0,5 and 1 million kilograms in 1986 with more than 2 million kilograms in 1990.

It is very much used in Forêt (to prepare and release the seedlings), for the weeding for the sowing of many cultures and like defoliant for some other cultures (Blé, Orge, Légume S, Colza or wild Moutarde, flax, fodder cultures, and or in the gardens by the private individuals and sometimes for the Culture without ploughing (which can avoid it while sowing under straw for example). The countries which authorized the culture of GMO saw its consumption increasing because many GMO are resistant to the glyphosate.

In water

The glyphosate is soluble there (12 g/L with 25 °C in fresh water). It was famous not very mobile and with weak risk of contamination of the tablecloths, but since one seeks it, one finds some in many water. It is more mobile and soluble in the grounds alkaline or rich in Phosphate (manures very much used by certain farmers). A study detected rates from 200 to 300 µg/L of glyphosate shortly after a direct pulverization in stagnant water. This rate was reduced only half after approximately three weeks. However Roundup could be legally or not used to weed ponds and ponds of fishing. The nature of the microbes present, the presence or absence of an important biofilm, the quantity of Ultraviolet, the temperature (season) and the pH probably also play a part in the speed of degradation of the glyphosate in water. Other sources quote a direct pulverization on lakes and ponds of 1 kg/ha followed by an initial concentration of 1.100 µg/L reduced to 149 µg/L after two days and 55 µg/L after five days.

In Sylviculture (with the Quebec) after pulverization, one in did not find (threshold of detection of 1,0 µg/L) in 8 cours d' water protected by a buffer zone from 30 m, but one found some in two samples coming from ditches (16,9 µg/L with max.). In the ponds having received a direct pulverization, the rate was of 2.800 µg/L in water right after pulverization, but had fallen with 288 µg/L 24 hours later. The kinetics of the glyphosate in the sediments seems little studied.

In the air

Its weak Tension of vapor (<1×10 -5 Pa with 25 °C) makes it not very soluble in the air, but it can be present there in the form of Aérosol or fixed on dust resulting from powdery ground and dry treaty. It can be to some extent degraded by photodécomposition under the effect of the Ultraviolet S of solar light.

Biochemistry

The mechanism of action of this pesticide is not entirely included/understood at present. It is known however that its phytotoxic action is due to the inhibition of the Enzyme 5-enolpyruvoyl-shikimate-3-phosphate synthase (EPSPS) implied in the metabolic way of the Shikimic acid . This way being absent in the animals, it was supposed of low toxicity on their premises. However, of many studies tend to show the opposite.

Uses and polemics

The glyphosate is in particular used by the government Colombia N, is helped by the government of the the United States in its Plan Colombia to destroy the fields of Coca producing drug which finances rebellious actions of groups. These actions destroy thousands of hectares of relics of tropical forest, sometimes classified Natural reserves, like the forest of the Putumayo, and the legal farms. The populations of these forests fear impacts on their health, like in the case of Roundup pulverized in Palestine, or, before, with the Orange Agent used like defoliant during the war of the Vietnam. The Amerindian communities are among the touched first. Close Ecuador fears also medical and ecological consequences Colombian fumigations of glyphosate close to its borders, in the Putumayo. The Colombian refusal to give up these air pulverizations caused in 2006-2007 a diplomatic crisis between the two countries.

The majority culture of soya GMO resistant to the glyphosate in Argentine involved a massive use of this weeding. Resistances appeared, bringing to the use of increasingly important amounts. The devegetalisation of the grounds, associated with the ploughing, is cause of loss of Humus, a devitalisation and a die-fertilization of the grounds. Humus --->

The polemic also related to the Biodégrabilité of weeding containing glyphosate. A manufacturer (Monsanto) lost a lawsuit because it had presented on his labels and posters the Roundup like dégradable or biodegradable (in the ground as in water). The half-life of the glyphosate (the time necessary so that 50% of the molecules of glyphosate are degraded) is, in conditions of laboratory, approximately 32 days in the ground and 3,3 days in water, an effectiveness varying according to the richness of the ground in Bactérie S, the temperature, the nature and the acidity of the ground, etc It would vary from 20 to 100 days depending on the state of the ground according to other sources. The glyphosate degrades in by-products, themselves not easily biodegradable, with deadlines varying according to the context.

The problem is that these figures seem to relate on the active matter and not to the surfactant one, nor on the possible synergistic impacts of the by-products of degradation, in particular when it are combined with the breakdown products of surfactant which could be one of the causes of toxicity of the product.

Contamination of the mediums (water, air, ground)

Lastly, the analyzes making it possible to detect the glyphosate in water were difficult, long and expensive a long time. They were thus rare. Since in the years 2000, of technological advances improved their precision and the costs decreased by it, aware is become that although dégradable, the glyphosate is very often present in water and the grounds. A study of IFEN (August 2006) showed that the glyphosate and AMPA, its breakdown product, were the substances most found in water in France. Indeed, the glyphosate is now the weedkiller more sold in France.

One started in the years 2000 to study the volatility and the kinetics of the glyphosate in the air (where one finds other pesticides which can also contaminate the rains), but measurements (in 2006/2007) are still very vague because the adsorbent resins charged to trap the glyphosate in the air of the analyzers fix it badly, part of the glyphosate being desorbed filter as the air passes there.

Moreover, being given the probable importance of synergies between products, products and molecules of degradation, and between all these molecules and those of the environment or of our organization, any unquestionable evaluation of the risk remains difficult being given the scarcity of the data and toxicological elements available. The first analyzes must be considered first indices and possibly of the elements of assistance to the precaution/Prévention.

Ecotoxicology

Some studies let think that the glyphosate could perhaps react with the Nitrite S present in certain food, but also in the agricultural ground S to form the N-nitrosophosphonométhylglycine, a possible Cancérogène.

Toxicology

DL50 of the pure glyphosate accounts for approximately 1% of the body weight. The immediate toxic effects are weak, even with high amounts. One however notes a notable reduction of the body weight and weight of the Foie. Several cases of Suicide by ingestion of weeding containing glyphosate showed that the commercial formulation (containing additives) is really Toxique, and with amounts much lower than the amounts of glyphosate which would be necessary to cause death, probably because of the toxicity and the synergistic effect of the surfactant one, which had been shown in experiments at Poisson S in particular.

The studies of laboratory, generally made or financed by manufacturing, showed that the introduced glyphosate was absorbed for 15 to 40% of the introduced amount. As for its first by-product of degradation (AMPA), it is absorbed at approximately 20% of the introduced amount.

Another study showed in monkeys that cutaneous absorption of a preparation of glyphosate was weak (2% after seven days of local application). But the transcutané passage can vary according to the species, the conditions (perspiration) and the age (at the human one, the skin of the children is for example much more permeable). An introduced amount (or injected (intrapéritonéale)), single or repeated during 12 days, is eliminated mainly via the urine, primarily in a not degraded form, although one finds also minor amounts of AMPA. The biliary excretion and entero-hepathic circulation are quantitatively tiny after 120 hours. A single amount of glyphosate was eliminated to 94% in the urines, in the males and the females (0,1% only of one amount being eliminated in the carbon dioxide shape marked 22), in condition of laboratory (animals not very mobile, not patients, nonexposed with the climatic risks, etc). The daily ingestion of glyphosate during 2 weeks results in maximum tissue concentrations at the sixth day of administration. The strongest concentrations being measured in the Kidney S (<1 Ppm), then in a decreasing way in the Spleen, fat fabrics, the Liver, the ovary S, the Heart and the Muscle S, residues decreasing gradually after the animal ceased introducing the product into its food, renal concentrations being of 0,1 ppm after 10 days.

It is delicate to draw the toxicological conclusions of the many studies made in the animal with pure glyphosate because in reality, it is an glyphosate-additive mixture which is likely to pose problem by contact or ingestion.

It nevertheless is proven that the glyphosate remains a powerful poison acting in particular on the cells Placenta human angers involving a multiplication of the late miscarriages.

Effectiveness and resistances

The glyphosate was initially shown extremely effective, then little by little appeared of the stocks bad resistant grasses. The cultures GMO resistant to the glyphosate, especially developed in the United States at the end of the years 1990, contributed to an increase in the use of the glyphosate in pieces GMO (93% of surfaces in Soja in the USA in 2006). It is in 2007 seven Adventice S which produced stocks resistant to this Pesticide, of which Ambrosia trifida (the Ambrosia trifide or Large Grass with lice) found in the Ohio and the Indiana, which is a plant which settles easily in the Soja, causing up to 70% of reduction in output. In France, INRA of Dijon confirmed in 2007 a first case of resistance to the glyphosate of a plant specie: the stiff Ryegrass (Lolium rigidum).

Some also fear that by pollution Génétique of the Crucifère S savages acquire the Transgène resistance to Glyphosate, and cannot be any more weeded in the fields or edges of road by weeding total based on the glyphosate.

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