Abstract
Glyphosate (GLYP), the globally most important herbicide, may have effects in various compartments of the environment such as soil and water. Although laboratory studies showed fast microbial degradation and a low leaching potential, it is often detected in various environmental compartments, but pathways are unknown. Therefore, the objective was to study GLYP leaching and transformations in a lysimeter field experiment over a study period of one hydrological year using non-radioactive 13C2-15N-GLYP labelling and maize cultivation. 15N and 13C were selectively measured using isotopic ratio mass spectrometry (IR-MS) in leachates, soil, and plant material. Additionally, HPLC coupled to tandem mass spectrometry (HPLC-MS/MS) was used for quantitation of GLYP and its main degradation product aminomethylphosphonic acid (AMPA) in different environmental compartments (leachates and soil). Results show low recoveries for GLYP (< 3%) and AMPA (< level of detection) in soil after the study period, whereas recoveries of 15N (11–19%) and 13C (23–54%) were higher. Time independent enrichment of 15N and 13C and the absence of GLYP and AMPA in leachates indicated further degradation. 15N was enriched in all compartments of maize plants (roots, shoots, and cobs). 13C was only enriched in roots. Results confirmed rapid degradation to further degradation products, e.g., 15NH4+, which plausibly was taken up as nutrient by plants. Due to the discrepancy of low GLYP and AMPA concentrations in soil, but higher values for 15N and 13C after the study period, it cannot be excluded that non-extractable residues of GLYP remained and accumulated in soil.
Highlights
Glyphosate (GLYP) is an important herbicide in the world, annually > 1 million tonnes are applied (Richmond 2018)
Rapid microbial degradation has been reported in soil, leading to the most predominant degradation product aminomethylphosphonic acid (AMPA)
GLYP frequently has been detected in ground and surface water (Coupe et al 2012) even above the regulatory limit of 0.1 μg L−1 in the EU (Van Stempvoort et al 2014; Skeff et al 2015)
Summary
Glyphosate (GLYP) is an important herbicide in the world, annually > 1 million tonnes are applied (Richmond 2018). GLYP can interact strongly with organic and inorganic molecules at a variety of binding sites such as (i) the soil organic matter, e.g., peptides, carbohydrates, or phenolic structures (Gros et al 2017; Ahmed et al 2018) or (ii) mineral surfaces, e.g., goethite or montmorillonite, as has been demonstrated in laboratory experiments and quantum chemical modeling (Morillo et al 1997; Ahmed et al 2017) These interactions lead to strong and high sorption, as has been shown in laboratory batch sorption experiments (Dion et al 2001; Okada et al 2016; Gros et al 2017). The mechanisms of GLYP translocation from place of application through the drainage system into waterways and estuaries are still unclear but need to be understood for preventing these undesired translocations
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