Issue |
Agron. Sustain. Dev.
Volume 28, Number 3, July-September 2008
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Page(s) | 419 - 428 | |
DOI | https://doi.org/10.1051/agro:2008014 | |
Published online | 03 June 2008 |
DOI: 10.1051/agro:2008014
Sorption and leaching of 14C-glyphosate in agricultural soils
Abdul Jabbar Al-Rajab, Samira Amellal and Michel SchiavonLaboratoire Sols et Environnement, UMR 1120 INPL/ENSAIA-INRA, 2 avenue de la Forêt de Haye, BP 172, 54505 Vandoeuvre-lès-Nancy Cedex, France
Accepted 28 February 2008; published online 3 June 2008
Abstract - Glyphosate (N-(phosphonomethyl)glycine) is one of the most
widely used herbicides in the world to control weeds in agricultural and
urban areas. Its increasing use requires special attention to its transfer
from terrestrial to aquatic environments. However, knowledge on the leaching
of glyphosate and its metabolite aminomethylphosphonic acid (AMPA) is
scarce. Here we aimed to assess the dynamic interactions between glyphosate
sorption and leaching; and to identify the main factors that influence the
two processes in three undisturbed agricultural soils using microlysimeters
under outdoor conditions. We studied the sorption, desorption and leaching
of 14C-labelled glyphosate on three soils using batch experiments in
the laboratory and lysimeters under natural conditions for 11 months. The
laboratory results showed that glyphosate was strongly adsorbed, yielding
empirical constants of Freundlich sorption isotherms (K of 16.6 for
the clay loam soil, 33.6 for the silt clay loam soil and 34.5 for the sandy
loam soil, with n
close to 1 in all three cases. Glyphosate was also
weakly desorbed, i.e. 5 to 24% (w) of initially sorbed glyphosate.
Sorption and desorption were only pH-dependent. The outdoor results showed
that nearly 70% of the initial glyphosate was present in the soil in a
non-extractable form at the beginning of the experiment. Conversely, only
less than 20% of the initial glyphosate is present in the soil in a
non-extractable form after 11 months. These findings suggest that the
non-extractable residues become available and take part in biodegradation
and leaching. The amounts of 14C-glyphosate derivatives leached were
less than 0.28% of the initially applied glyphosate. HPLC analyses showed
that the AMPA metabolite generally represented up to 100% of the residues present in the
leachates. The results of leaching were highly influenced by the
hydrodynamic properties and the biodegradation capacities of the soils.
Although glyphosate residues were found in low concentrations in the
leachates for almost a year, the contamination of groundwater does not seem
to be a concern, regardless of the soil type, if the herbicide is used in
accordance with good agricultural practice.
Key words: glyphosate / adsorption / desorption / leaching / sequestration / persistence / soil lysimeters
Corresponding author: michel.schiavon@ensaia.inpl-nancy.fr
© INRA, EDP Sciences 2008