How long does Roundup last in the soil?

Date:   11/22/2011 5:42:47 AM ( 13 y ago)

How long does Roundup last in the soil?

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


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