Roundup herbicide in Soil Effects by YourEnchantedGardener Blog entry

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Roundup herbicide in Soil Effects

Roundup herbicide in Soil Effects

Date: 11/22/2011 5:24:45 AM ( 13 y ) ... viewed 1161 times

4Environmental fate When glyphosate is introduced into the environment a number of processes appear to
determine its fate. The most important include:
C the formation of complexes in water with ions such as Ca2+, Mg2+ C sorption to sediment or suspended particles C suspended particles in water and soil C uptake and metabolism by plants
C biodegradation by micro-organisms.
A range of bacterial strains can degrade glyphosate using the compound as a source of phosphorus, carbon, or nitrogen. The major breakdown product or metabolite of glyphosate is aminomethylphosphonic acid (AMPA). Carbon dioxide is also a breakdown product7.
4.1 Persistence in soil and water
The agrochemical company Zeneca claims that its product, Touchdown, a herbicide containing glyphosate trimesium, is “rapidly inactivated and broken down in the soil”46. Monsanto has measured the half life of glyphosate (the time required for half the amount to biodegrade or dissipate) and determined it to vary between three and 141 days.
In the field, long persistence of glyphosate has been observed in a number of studies. AMPA has been found to be even more persistent than glyphosate, with a half life in soil between 119 and 958 days7. In water, glyphosate has a long persistence in sediments. Records of glyphosate persistence include47:
C 249 days on Finnish agricultural soils. C between 259 and 296 days on eight Finnish forestry sites. C between one and three years on 11 Swedish forestry sites. C 335 days on a Canadian forestry site. C 360 days on three Canadian forestry sites. C two Canadian studies found glyphosate persisted 12 to 60 days in pond water
following direct application
15 Health and environmental impacts of glyphosate
C glyphosate residues in pond sediment were found 400 days after direct application with the formulation Accord
C glyphosate was found to persist for more than one year in studies of pond sediments in the US
C studies in Norway have detected glyphosate in surface and ground waters48. 4.2 Mobility in soil
Monsanto claims glyphosate is essentially immobile in soil9. The belief that glyphosate readily and permanently binds to soil particles and remains in the upper few centimetres of soil has greatly increased its popularity and use. In reality, there is very little information available on the behaviour of glyphosate in soils49. The mechanism of sorption to soil is not fully understood, although it is believed that metal complexes with humic acid in soil may be the main binding mechanism7.
Recent studies have cast important questions over the extent to which glyphosate is immobile in soil. One such study has shown that glyphosate can readily desorb from soil particles in some soil types and can be highly mobile in the soil environment (see below)50. Four soils, chosen to represent the most widespread soil types in the EU, were used in the study. The key findings included:
C Levels of adsorption of glyphosate varied in the different soils according to their composition. Least adsorption occurred in the soils containing lower levels of iron oxide. The clay mineral content was also found to be important. Soils containing higher levels of clay minerals adsorbed more glyphosate. However, desorption readily occurred in soil with a high clay mineral but low iron oxide content.
C Large parts of the fixed herbicide can be easily returned to the soil solution. C The least adsorbing soils desorbed up to 80 per cent of the adsorbed herbicide and
the high adsorbing soils released between 15 and 35 per cent of the glyphosate
adsorbed. C In soils that are unable to bind with glyphosate long enough for microbial
degradation to take place, the herbicide can be extensively mobile in the soil
environment. C Desorbed glyphosate can leach to lower soil layers. C Glyphosate can bond with water soluble humic substances found in soil solution.
Humic substances are the soil components primarily responsible for the mobility of pesticides in soil. Glyphosate can be transported with humic substances to lower soil depths50.
Other recent studies have found:
C Adsorption of glyphosate on clay minerals decreased in the presence of copper, due to the formation of glyphosate-copper complexes. The study concluded that in relation to glyphosate release and mobility in soil, it is necessary to take into account both the soil type and any element in the soil capable of forming complexes with glyphosate51.
C A study of sandy soils in Western Australia found that adsorption of glyphosate and Health and environmental impacts of glyphosate 16

Roundup herbicide in Soil Effects

The introduction of genetically modified crops tolerant to glyphosate will lead to a significant increase in the use of this herbicide. Monsanto, the company producing these crops, claims that their introduction will be of benefit because of the low toxicity and environmental safety of the herbicide. Monsanto, it should be noted, also manufactures glyphosate, marketing it as ‘Round up’, and so is able to sell seeds and herbicide as a commercial package. Independent research indicates that glyphosate may not be as safe as previously thought and may pose a threat to human health and the environment. It is essential that questions relating to the safety of this product are answered before its use is scaled up with the introduction of genetically modified crops. The following table provides a comparison of Monsanto’s claims and the findings of independent research.
Monsanto*s claims
Independent research findings
Roundup has a low irritation potential for eye and skin and otherwise is not a risk to human health.
C Roundup is amongst the top most-reported pesticides causing poisoning incidents in several countries.
C Roundup causes a range of acute symptoms including recurrent eczema, respiratory problems, elevated blood pressure and allergic reactions.
Roundup does not cause any adverse reproductive effects.
C In laboratory tests on rabbits glyphosate caused long- lasting, harmful effects on semen quality and sperm counts.
Roundup is not mutagenic in mammals.
C DNA damage has been observed in laboratory experiments in mice organs and tissue.
Roundup is environmentally safe.
C In the agricultural environment, glyphosate is toxic to beneficial soil organisms and beneficial arthropod predators, and increases crops* susceptibility to diseases.
C The use of glyphosate in forestry and agriculture has indirect harmful effects on birds and small mammals by damaging their food supplies and habitat.
C Roundup containing POEA is lethal to the tadpoles of three species of tree and ground frogs in Australia. The Australian government has banned the use of these products near water.
C Sub-lethal doses of glyphosate from spray-drift damages wildflower communities and can affect some species up to 20 metres away from the sprayer.
C The use of glyphosate in arable areas causes dieback in hedgerow trees.
C Glyphosate promotes population growth of a water snail that is the intermediate host of liver fluke in mammals.
C The breakdown of glyphosate by micro-organisms in water may stimulate eutrophication effects.
1
Roundup is rapidly inactivated in the soil and water.
C Glyphosate is very persistent in soils and sediments. C Glyphosate inhibited the formation of nitrogen-fixing
nodules on clover for 120 days after treatment. C Glyphosate residues were found in lettuce, carrot and barley when they were planted a year after glyphosate
was applied. C Phosphate fertilisers may inhibit breakdown in soil.
Roundup is immobile and does not leach from soils.
C Glyphosate can readily desorb from soil particles in a range of soil types. It can be extensively mobile and leach to lower soil layers.
C Glyphosate can be carried by soil particles suspended in run off.
Roundup does not contaminate drinking water when used by local authorities on hard surfaces.
C In the UK, levels of glyphosate above the EU limit have been detected by the Welsh Water Company every year since 1993. The Drinking Water Inspectorate recommends that glyphosate be monitored, particularly in areas where it is used by local authorities on hard surfaces.
It is nearly impossible for glyphosate resistance to evolve in weeds.
C In 1996, glyphosate-resistant ryegrass was discovered in Australia.
Outcrossing from GM crops and the transfer of novel genes occurs over a short distance and can be easily managed.

C In those crops which have been examined, the densities of pollen are much higher and their dispersal patterns differ from large fields compared to those found in experimental plots. Wind dispersal of pollen occurs over much greater distances and at higher concentrations than predicted by experimental plots. Gene flow from transgenic oil seed crops is inevitable.
Roundup Ready crops will reduce levels of herbicide use.
C Herbicide-tolerant crops will intensify and increase dependency on herbicide use in agriculture rather than lead to any significant reductions. A variety of herbicides will have to be reintroduced to control glyphosate-tolerant volunteers, feral populations of crops and resistant weeds.
Sources: Monsanto Company, 1985, Toxicology of Glyphosate and Roundup Herbicide. Monsanto Company, Department of Medicine and Environmental Health, Missouri, USA; Monsanto Company, Web Site: http://www.monsanto.com.,
18th January 1998; Monsanto Advertising Supplements in Farmers*s Weekly, Roundup 91, 7 June 1991, and Roundup 92, 5th June 1992; Pesticide Outlook, Dec. 1997, Royal Society of chemistry, Vol. 8, No. 6, pp3-4.

http://www.foe.co.uk/resource/reports/impacts_glyphosate.pdf