Glyphosate translocation from plants to soil – does this constitute a significant proportion of residues in soil?

Abstract

Translocation of glyphosate (N-(phosphonomethyl)glycine) to plant roots and its impact on detected herbicide residues in sandy loam soil were studied in a glasshouse pot experiment in Finland. Quinoa (Chenopodium quinoa, Willd) plants in two different growing phases (6-8 and 12-14 leaf stages, groups A and B, respectively) were sprayed with nonlabelled glyphosate. Bare soil pots were included as controls (group C). Soil surface contamination with glyphosate was prevented in groups A and B but not in group C. Soil samples were collected 1 h, 8 days and 44 or 53 days after the glyphosate applications. Root samples were taken 8 days after the application from group B. After 8 days from the treatment, 4% of the applied glyphosate was detected in soil and about 12% in roots (group B). One and a half months later 12% and 8% of the applied glyphosate (groups A and B, respectively) was detected in soil samples incubated with roots. The main metabolite of glyphosate, aminomethyl phosphonic acid (AMPA), was not found in root samples. Glyphosate fate was simulated with the PEARL 3.0 model. Simulated concentrations in bare soil pots were very close to the observed ones. However, the model lacks a process description for herbicide transport within a plant and, therefore, the observed and simulated glyphosate residues in soil after canopy applications did not correlate. Simulations highlight the importance of the translocation process in glyphosate fate. We conclude that also in field studies part of the detected glyphosate soil residues must originate from plant roots, and translocation process should be included both in leaching assessments and pesticide fate models.

Distribution of glyphosate and aminomethylphosphonic acid (AMPA) in agricultural topsoils of the European Union

“…In fact, despite some recent studies on the distribution of glyphosate and AMPA in soils from Argentina (e.g., Aparicio et al, 2013;Lupi et al, 2015;Primost et al, 2017), U.S.A. (e.g., Battaglin et al, 2014;Scribner et al, 2007) or Australia (e.g., Todorovic et al, 2013), in Europe, where the approval for GlyBH use will be decided by the end of 2017, information on occurrence and levels of these substances in soil is still very limited and out of date (Grunewald et al, 2001;Laitinen et al, 2006Laitinen et al, , 2007Laitinen et al, , 2009. The European long term use of GlyBH, as the most sold herbicide in Europe, urgently require monitoring of residues in agricultural soils.…”

Impact of phosphate on glyphosate uptake and toxicity in willow

“…Inorganic phosphate (PO 4 3-) and glyphosate's methylphosphonic group compete for similar adsorbing sites [9,10], and, as a result, glyphosate sorption and its availability in soil solution are determined by the soil's capacity to adsorb PO 4 3-. Phosphorous is an essential nutrient, participating in crucial metabolic events, such as energy transfer and protein metabolism in plants [11], and PO 4 3-fertilization of soil is a common agricultural practice to assure plant growth and development [12]. PO 4 3-fertilization of agricultural fields submitted to glyphosate application may invariably influence the herbicide's bioavailability in soil solution, since the two compete for soil adsorbing sites [13]. Like PO 4 3-, glyphosate has high water solubility [6] and can easily be transferred to aquatic systems through runoff.…”

Soil and Environmental Health after Twenty Years of Intensive Use of Glyphosate

“…13 Although glyphosate use has increased nearly 15-fold since 1996 14 when glyphosate-resistant GE crops were first introduced, it is only within the last 5 to 10years that assessment of its detrimental effects on soil and environmental health have become the focus of intensive research efforts. Recent findings that glyphosate tends to accumulate and persist in restricted zones of soils and sediments and in rhizospheres [5][6][7]11,12 emphasizes the need to evaluate environmental effects within these specific microhabitats relative to more traditional investigations of such chemicals amended in "bulk" or root-free homogenous soils and expressing concentrations on a "furrow-slice" basis (i.e., using 908,000kg of soil per ha). For a full understanding of effects of potential glyphosate accumulation in soils, long-term studies on persistence are needed on sites receiving annual application and on those that are no longer under GE cropping systems to determine the extent of any carryover of residual glyphosate and AMPA.…”

“…4 Based on a limited number of studies available, glyphosate residues detected in soils of crop production fields range from 25 to 1000μg kg -1 soil. [5][6][7] Concentrations exceeding 1000μg kg -1 of soil have been detected in silt loam soils of northeast Missouri U.S.A. more than one year after the last application (Kremer, unpublished data). As frequency of glyphosate application increases during the crop season and with annual use, residual concentration likely builds up and persists in soils because about 5% of the applied dose reaches the target weed while the remaining amount contacts the soil surface or is released by roots of plants intercepting the glyphosate, and from vegetative residues treated plants during decomposition.…”

“…As frequency of glyphosate application increases during the crop season and with annual use, residual concentration likely builds up and persists in soils because about 5% of the applied dose reaches the target weed while the remaining amount contacts the soil surface or is released by roots of plants intercepting the glyphosate, and from vegetative residues treated plants during decomposition. [6][7][8][9] The revelation of potential widespread soil persistence contradicts the assumed rapid immobilization, degradation, and sorption of glyphosate in soils, raising concerns about non-target effects on the environment. However considerable research over the past ten years has shown that characteristics in diverse soils combined with various crop management practices influence the activity of glyphosate and demonstrate that its association with soil colloids, organic matter and water may have potential adverse effects on plant nutrient availability, phytotoxicity to non-GE crops, and soil microbial diversity and function.…”