Dissipation of glyphosate and aminomethylphosphonic acid in water and sediment of two Canadian prairie wetlands

Abstract

Glyphosate [N-(phosphonomethyl)glycine] is the active ingredient of several herbicide products first registered for use in 1974 under the tradename Roundup. The use of glyphosate-based herbicides has increased dramatically over the last two decades particularly in association with the adoption of glyphosate-tolerant crops. Glyphosate has been detected in a range of surface waters but this is the first study to monitor its fate in prairie wetlands situated in agricultural fields. An ephemeral wetland (E) and a semi-permanent wetland (SP) were each divided into halves using a polyvinyl curtain. One half of each wetland was fortified with glyphosate with the added mass simulating an accidental direct overspray. Glyphosate dissipated rapidly in the water column of the two prairie wetlands studied (DT(50) values of 1.3 and 4.8 d) which may effectively reduce the impact of exposure of aquatic biota to the herbicide. Degradation of glyphosate to its major metabolite aminomethylphosphonic acid (AMPA) and sorption of the herbicide to bottom sediment were more important pathways for the dissipation of glyphosate from the water column than movement of the herbicide with infiltrating water. Presently, we are not aware of any Canadian guidelines for glyphosate residues in sediment of aquatic ecosystems. Since a substantial portion of glyphosate entering prairie wetlands will become associated with bottom sediments, particularly in ephemeral wetlands, guidelines would need to be developed to assess the protection of organisms that spend all or part of their lifecycle in sediment.

Glyphosate and aminomethylphosphonic acid chronic risk assessment for soil biota

“…Therefore, no cosolvent was required, and both stock solutions of glyphosate and AMPA test items were prepared in deionized water (5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20) …”

“…The results of environmental fate studies show that glyphosate is stable to photolytic and hydrolytic degradation in sterile water in all environmentally relevant pH ranges. In contrast, glyphosate is degraded by microorganisms in soil, nonsterile water, and water and sediment systems [2,8]. In soil, microflora degrade glyphosate, under both aerobic and anaerobic conditions [2].…”

Short-term transport of glyphosate with erosion in Chinese loess soil — A flume experiment

“…The solubility of glyphosate contributes much to its contamination of surface water, but glyphosate and AMPA bound to particles suspended in water is another means of glyphosate and AMPA transport, known as particle-facilitated transport (Rügner et al, 2014;VandeVoort et al, 2013). Degenhardt et al (2012) reported that 67% of added glyphosate was detected in wetland sediment monitoring within 77 days from June to September. Leaching with drainage is another method of glyphosate and AMPA transport that may lead to potential contamination of, and accumulation in, groundwater (Kjaer et al, 2011;Ruiz-Toledo et al, 2014;Ulén et al, 2012).…”

Organic phosphorus in the aquatic environment

“…An alternate approach to determining fluxes in aquatic environments is following the fate of a particular compound that has either accidently or deliberately been added to a water body (known as 'spiralling experiments' when carried out in flowing systems). Examples of this approach include studies that have observed the fate of glyphosate and its hydrolysis product (aminomethylphosponic acid) experimentally applied to prairie wetlands [138] and changes in organic P speciation with distance from a poultry operation. [87] However, because of the logistics in performing these types of experiments, they are often restricted to small water bodies like drains, creeks and wetlands.…”