Modelling the Environmental Fate of the Herbicide Glyphosate in Soil Lysimeters

Abstract

In a risk assessment study the environmental fate of the herbicide glyphosate was studied with the specific background of the presence of genetically modified (GM) plants. Aim was to simulate the environmental behaviour of glyphosate in sandy field soil lysimeters after multiple herbicide applications and under the presence of GM soybean and to test and enhance model reliability in the simulation of the herbicide fate including biodegradation in the soil and herbicide translocation in GM plants. The modelling of the herbicide behaviour in the present study was based on the pesticide transport model LEACHP and the model PLANTX to simulate the pesticide uptake by plants. Both models were implemented in the modular modelling system EXPERT-N. Glyphosate transport measurements and the mathematical modelling results indicate that due to the high sorption of glyphosate to the soil matrix and the high microbial capacities for glyphosate degradation in the lysimeter soil, leaching risk can be considered to be low. We confirmed that the introduction of more adequate conceptual descriptions of microbial response to pesticide and nutrient additions can contribute to a reduction in the uncertainty of pesticide degradation modelling. Moreover, the consideration of uncertainty in sorption, dispersivity and degradation parameters revealed a considerable variability in model output. The observed accumulation of glyphosate in roots and nodules was reproduced by the simulation results. Under the restriction that the prevailing model assumptions are valid, the simulation results indicate that glyphosate may accumulate also in beans of trangenic soybean.

Monitoring of Water and Solute Transport in the Vadose Zone: A Review

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Scientific Opinion on an application (EFSA‐GMO‐NL‐2005‐24) for the placing on the market of the herbicide tolerant genetically modified soybean 40‐3‐2 for cultivation under Regulation (EC) No 1829/2003 from Monsanto

“…All of the factors above vary from region to region, from Member State to Member State, from season to season, and from biodiversity component to biodiversity component. For these reasons, whilst meaningful conclusions can be drawn from general principles, the EFSA GMO Panel acknowledges that there are 2008; Duke and Powles, 2008b;Gardner and Nelson, 2008;Klier et al, 2008;Shipitalo et al, 2008;Struger et al, 2008;Arregui et al, 2010;Dewar, 2010;Mamy et al, 2010;Stewart et al, 2011 considerable challenges to making accurate predictions on the environmental consequences of the use of herbicides in different GMHT cropping systems. Predictions from models would need to consider all the issues detailed above, over the full range of possible parameters that may be varied in the management of the GMHT crops, and the full range of receiving environments within Europe.…”

On glyphosate

“…Sprayed on the leaves glyphosate is rapidly taken up and translocated into the newly developing plant parts (Klier et al, 2008), and appreciable amounts are exuded from the roots into the soil solution (Coupland and Caseley, 1979). In many soils, glyphosate is not readily decomposed and may remain there for a long period of time unchanged or chelated with soil cations.…”