Degradation of 14C-glyphosate and aminomethylphosphonic acid (AMPA) inthree agricultural soils

Glyphosate (N-phosphonomethyl glycine) is the most used herbicide worldwide. The degradation of 14C-labeled glyphosate wasstudied under controlled laboratory conditions in three di erent agricultural soils: a silt clay loam, a clay loam and a sandy loam soil.The kinetic and intensity of glyphosate degradation varied considerably over time within the same soil and among di erent types ofsoil. Our results demonstrated that the mineralization rate of glyphosate was high at the beginning of incubation and then decreasedwith time until the end of the experiment. The same kinetic was observed for the water extractable residues. The degradation ofglyphosate was rapid in the soil with low adsorption capacity (clay loam soil) with a short half-life of 4 days. However, the persistenceof glyphosate in high adsorption capacity soils increased, with half-live of 19 days for silt clay loam soil and 14.5 days for sandyloam soil. HPLC analyses showed that the main metabolite of glyphosate, aminomethylphosphonic acid (AMPA) was detected afterthree days of incubation in the extracts of all three soils. Our results suggested that the possibility of contamination of groundwater byglyphosate was high on a long-term period in soils with high adsorption capacity and low degrading activities and/or acid similar tosandy loam soil. This risk might be faster but less sustainable in soil with low adsorption capacity and high degrading activity like theclay loam soil. However, the release of non-extractable residues may increase the risk of contamination of groundwater regardless ofthe type of soil.