Environmental fate of herbicides trifluralin, metazachlor, metamitron and sulcotrione compared with that of glyphosate, a substitute broad spectrum herbicide for different glyphosate‐resistant crops

Abstract

The introduction of crops resistant to the broad spectrum herbicide glyphosate, N-(phosphonomethyl)glycine, may constitute an answer to increased contamination of the environment by herbicides, since it should reduce the total amount of herbicide needed and the number of active ingredients. However, there are few published data comparing the fate of glyphosate in the environment, particularly in soil, with that of substitute herbicides. The objective of this study is to compare the fate of glyphosate in three soils with that of four herbicides frequently used on crops that might be glyphosate resistant: trifluralin, alpha,alpha,alpha-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine, and metazachlor, 2-chloro-N-(pyrazol-1-ylmethyl)acet-2',6'-xylidide for oilseed rape, metamitron, 4-amino-4,5-dihydro-3-methyl-6-phenyl-1,2,4-triazin-5-one for sugarbeet and sulcotrione, 2-(2-chloro-4-mesylbenzoyl)cyclohexane-1,3-dione for maize. The distribution of herbicides between the volatilized, mineralized, extractable and non-extractable fractions was studied, along with the formation of their metabolites in laboratory experiments using 14C-labelled herbicides, over a period of 140 days. The main dissipation pathways were mineralization for glyphosate and sulcotrione, volatilization for trifluralin and non-extractable residues formation for metazachlor and metamitron. The five herbicides had low persistence. Glyphosate had the shortest half-life, which varied with soil type, whereas trifluralin had the longest. The half-lives of metazachlor and sulcotrione were comparable, whereas that of metamitron was highly variable. Glyphosate, metazachlor and sulcotrione were degraded into persistent metabolites. Low amounts of trifluralin and metamitron metabolites were observed. At 140 days after herbicide applications, the amounts of glyphosate and its metabolite residues in soils were the lowest in two soils, but not in the third soil, a loamy sand with low pH. The environmental advantage in using glyphosate due to its rapid degradation is counterbalanced by accumulation of aminomethylphosphonic acid specifically in the context of extensive use of glyphosate.

Influence of soil tillage and erosion on the dispersion of glyphosate and aminomethylphosphonic acid in agricultural soils

“…As shown in a previous study by Mamy et al (2005), this could be explained because the two compounds are very quickly adsorbed by the soil compounds, probably also depending on the physical soil conditions and water flow during rainfall. In fact, the Chernozem had a favourable crumby structure in the NT-plots, with no cracks, no preferential flow, and optimal conditions for water retention in the upper soil layers at the moment of the rainfall simulation experiment, so that more than 50% of the adsorbed glyphosate was retained in the first 5 cm of the soil.…”

“…Like for many other organic contaminants, the distribution of glyphosate in soils and the environment is strongly governed by different soil constituents and processes as well as by specific local site conditions (Eberbach, 1997;Gimsing et al, 2004;Mamy et al, 2005;Soulas and Lagacherie, 2001). The investigation of the pathways of glyphosate and AMPA in the environment and their interaction with different soils is therefore of major interest for assessing their Int.…”

Early Detection of Crop Injury from Glyphosate on Soybean and Cotton Using Plant Leaf Hyperspectral Data

“…Aminomethylphosphonic acid, the main metabolite of glyphosate, will be found in the leaves of these glyphosate treated plants [8]. It exhibits a half-life of 25-75 days and is known to cause chlorosis of leaves, which would cause a continuing injury to non-GR plants [9]. Therefore, foliar biochemistry is a potential indicator of glyphosate injury for non-GR crops, and the leaf injuries from glyphosate are always accompanied by reduction of chlorophyll content.…”

Adsorption of glyphosate and aminomethylphosphonic acid in soils

“…The behaviour of organic contaminants in soils is generally governed by a variety of physical, chemical and biological processes, including sorption-desorption, volatilization, chemical and biological degradation, uptake by plants, run-off, and leaching (Mamy et al, 2005).…”