Leaching and degradation of 13C2-15N-glyphosate in field lysimeters

Nitrogen-fertilizer addition to an agricultural soil enhances biogenic non-extractable residue formation from 2-13C,15N-glyphosate

Glyphosate and nitrogen (N) or (P) phosphorus fertilizers are often applied in combination to agricultural fields. The additional P or N supply to microorganisms might drive glyphosate degradation towards sarcosine/glycine or aminomethylphosphonic acid (AMPA), and consequently determine the speciation of non-extractable residues (NERs): harmless biogenic NERs (bioNERs) or potentially hazardous xenobiotic NERs (xenoNERs). We therefore investigated the effect of P or N-fertilizers on microbial degradation of glyphosate and bioNER formation in an agricultural soil. Four different treatments were incubated at 20 °C for 75 days as follows; I: no fertilizer (2-13C,15N-glyphosate only, control), II: P-fertilizer (superphosphate + 2-13C,15N-glyphosate, effect of P-supply), III: N-fertilizer (ammonium nitrate + 2-13C,15N-glyphosate, effect of N-supply) and IV: 15N-fertilizer (15N-ammonium nitrate + 2-13C-glyphosate, differentiation between microbial assimilations of 15N: 15N-fertilizer versus 15N-glyphosate). We quantified 13C or 15N in mineralization, extractable residues, NERs and in amino acids (AAs). At the end, mineralization (36-41 % of the 13C), extractable 2-13C,15N-glyphosate/2-13C-glyphosate (0.42-0.49 %) & 15N-AMPA (1.2 %), and 13C/15N-NERs (40-43 % of the 13C, 40-50 % of the 15N) were comparable among treatments. Contrastingly, the 15N-NERs from 15N-fertlizer amounted to only 6.6 % of the 15N. Notably, N-fertilizer promoted an incorporation of 13C/15N from 2-13C,15N-glyphosate into AAs and thus the formation of 13C/15N-bioNERs. The 13C/15N-AAs were as follows: 16-21 % (N-fertilizer) > 11-13 % (control) > 7.2-7.3 % (P-fertilizer) of the initially added isotope. 2-13C,15N-glyphosate was degraded via the sarcosine/glycine and AMPA simultaneously in all treatments, regardless of the treatment type. The percentage share of bioNERs within the NERs in the N-fertilized soil was highest (13C: 80-82 %, 15N: 100 %) compared to 53 % (13C & 15N, control) and to only 30 % (13C & 15N, P-fertilizer). We thus concluded simultaneous N & glyphosate addition to soils could be beneficial for the environment due to the enhanced bioNER formation, while P & glyphosate application disadvantageous since it promoted xenoNER formation.

Fate of glyphosate and its degradation products AMPA, glycine and sarcosine in an agricultural soil: Implications for environmental risk assessment

Glyphosate can be biodegraded via the aminomethylphosponic acid (AMPA) and the sarcosine/glycine pathway leading to the formation of three intermediate products AMPA, sarcosine or glycine. The fate of the three intermediate compounds of glyphosate biodegradation including nature of non-extractable residues (NERs; harmless biogenic [NERs_biogenic] versus hazardous xenobiotic [NERs_xenobiotic]) in soils has not been investigated yet. This information is crucial for an assessment of environmental risks related to the speciation of glyphosate-derived NERs which may stem from glyphosate intermediates. Therefore, we incubated ¹³C- and ¹⁵N-labeled glyphosate (2-¹³C,¹⁵N-glyphosate) and its degradation product AMPA (¹³C,¹⁵N-AMPA), sarcosine (¹³C₃,¹⁵N-sarcosine) or glycine (¹³C₂,¹⁵N-glycine) in an agricultural soil separately for a period of 75 days. ¹³C₂-glycine and ¹³C₃-sarcosine mineralized rapidly compared to 2-¹³C-glyphosate and ¹³C-AMPA. The mineralization of ¹³C-AMPA was lowest among all four compounds due to its persistent nature. Only 0.5% of the initially added 2-¹³C,¹⁵N-glyphosate and still about 30% of the initially added ¹³C,¹⁵N-AMPA was extracted from soil after 75 days. The NERs formed from ¹³C,¹⁵N-AMPA were mostly NERs_xenobiotic as compared to other three compounds for which significant amounts of NERs_biogenic were determined. We noticed 2-¹³C,¹⁵N-glyphosate was biodegraded via two biodegradation pathways simultaneously; however, the sarcosine/glycine pathway with the formation of harmless NERs_biogenic presumably dominated.

Glyphosate pollution of surface runoff, stream water, and drinking water resources in Southeast Brazil

Glyphosate-based herbicides can be harmful to the environment and human health. Especially in developing countries, these herbicides are often used indiscriminately in agricultural and urban areas. Here, we optimized a simple and efficient flow injection-based spectrophotometric method to monitor environmentally relevant glyphosate concentrations in surface waters. The method was then used to assess the environmental mobility of glyphosate in Southeast Brazil by monitoring surface runoff from experimental agricultural soil plots that received glyphosate applications in 2015. Further, water samples from low-order streams were collected in five agricultural, urban, and natural areas, as well as from the 5th-order Rio das Mortes during the rainy season. Finally, 20 drinking water sources were sampled in urban, rural, and agricultural areas. Runoff from reference plots without glyphosate application showed concentrations below the method's detection limit of 0.49 mg.L^-1, whereas runoff from plots with standard glyphosate application had concentrations between 1.24 and 6.1 mg.L^-1. Similarly, concentrations in natural stream water were below the detection limit, whereas agricultural streams had concentrations of up to 3.7 mg.L^-1 (average: 0.97 mg.L^-1). In an agricultural stream monitored weekly, concentration peaks were observed after glyphosate applications by farmers, and concentrations were correlated to stream discharge. Urban streams had concentrations of up to 5.8 mg.L^-1 (average: 2.6 mg.L^-1), but samples from the catchment's major river were mostly below detection limits, illustrating the dilution of urban and agricultural runoff in high-order rivers. In the sampled drinking water resources, glyphosate pollution occurred mainly in the rainy season, with detectable concentrations between 0.5 and 8.7 mg.L^-1 in 80% of the sampled drinking water sources. In conclusion, our results suggest considerable environmental mobility of glyphosate in the studied Southeast Brazilian catchment. Substantial pollution, well above national and international limits, was detected in surface runoff, stream water, and drinking water resources.

A comprehensive experimental assessment of glyphosate ecological impacts in riparian forest restoration

Competition with invasive grasses is one of the most important drivers of tree planting failures, especially in tropical forests. A widely disseminated weeding approach has been glyphosate spraying, the most used herbicide globally in forestry and ecosystem restoration. However, glyphosate use in restoration is highly controversial and requires further studies to elucidate its effects on restoration processes and the environment. We evaluated the use of glyphosate in riparian forest restoration and its impacts on tree planting costs, weed control efficiency, planted seedling performance, herbaceous and woody species regeneration, soil bacteria, and environmental contamination, using mowing treatments as a reference and based on a controlled experiment established in the Brazilian Atlantic Forest. Glyphosate spraying reduced by one-half and one-third the accumulated aboveground biomass of, respectively, weeds in general and of the invasive grass Urochloa decumbens compared to mowing treatments, and it reduced the cost by half. The performance of planted tree seedlings was markedly favored by glyphosate spraying compared to mowing treatments, as expressed by improved seedling height (~twice higher), crown area (~5× higher), and basal area (~5× higher); the regeneration of both native woody and ruderal herbaceous plants were also enhanced. Neither glyphosate nor its metabolite Aminomethylphosphonic acid (AMPA) residues were detected in either water runoff or soil samples, but they were found at relatively high concentrations in the runoff sediments (from 1.32 to 24.75 mg/kg for glyphosate and from 1.75 to 76.13 mg/kg for AMPA). Soil bacteria communities differed before and after glyphosate spraying in comparison to mowing plots (without glyphosate). Glyphosate spraying was far more cost effective than mowing for controlling U. decumbens and greatly improved the performance of planted tree seedlings and natural regeneration, while not leaving residues in soil and water. However, the changes in the structure of bacterial communities and high concentration of glyphosate and AMPA residues in runoff sediments highlight the need for caution when using this herbicide in riparian buffers. We present alternatives for reducing glyphosate use and minimizing its risks in tree planting initiatives.

AMPA-15N - Synthesis and application as standard compound in traceable degradation studies of glyphosate

Stable isotope labeling of pollutants is a valuable tool to investigate their environmental transport and degradation. For the globally most frequently used herbicide glyphosate, such studies have, so far, been hampered by the absence of an analytical standard for its labeled metabolite AMPA-15N, which is formed during the degradation of all commercially available glyphosate isotopologues. Without such a standard, detection and quantitation of AMPA-15N, e.g. with LC-MS/MS, is not possible. Therefore, a synthetic pathway to AMPA-15N from benzamide-15N via the hemiaminal was developed. AMPA-15N was obtained in sufficient yield and purity to be used as a standard compound for LC-MS/MS analysis. Suitable MS-detection settings as well as a calibration using the internal standard (IS) approach were established for Fmoc-derivatized AMPA-15N. The use of different AMPA isotopologues as IS was complicated by the parallel formation of [M+H]+ and [M]+• AMPA-Fmoc precursor ions in ESI-positive mode, causing signal interferences between analyte and IS. We recommend the use of either AMPA-13C-15N, AMPA-13C-15N-D2 or a glyphosate isotopologue as IS, as they do not affect the linearity of the calibration curve. As a proof of concept, the developed analysis procedure for AMPA-15N was used to refine the results from a field lysimeter experiment investigating leaching and degradation of glyphosate-2-13C-15N. The newly enabled quantitation of AMPA-15N in soil extracts showed that similar amounts (0.05 - 0.22 mg·kg-1) of the parent herbicide glyphosate and its primary metabolite AMPA persisted in the topsoil over the study period of one year, while vertical transport through the soil column did not occur for either of the compounds. The herein developed analysis concepts will facilitate future design and execution of experiments on the environmental fate of the herbicide glyphosate.

The carbon stable isotope compositions of glyphosate and aminomethylphosphonic acid (AMPA): Improved analytical sensitivity and first application to environmental water matrices

RATIONALE

The presence of glyphosate and its degradation product aminomethylphosphonic acid (AMPA) in the environment has adverse effects on environmental quality, raising the need to better constrain their fates, in particular the processes that control their production and degradation. Our aim was to improve the sensitivity of their δ¹³ C analysis and demonstrate the feasibility of measuring them in natural surface water.

METHODS

The δ¹³ C values of dissolved glyphosate and AMPA were determined using isotope ratio mass spectrometry (IRMS) (Delta V Plus instrument) coupled to a high-performance liquid chromatography (HPLC) unit, where glyphosate and AMPA were separated on a Hypercarb column.

RESULTS

We demonstrated an improved sensitivity of the δ¹³ C analysis for glyphosate and AMPA by LC/IRMS compared with previous studies. For waters from the carbonate and silicate hydrofacies, while no pretreatment was required for the isotope analysis of glyphosate, removal by H₃ PO₄ acidification of dissolved inorganic carbon, that co-elutes with AMPA, was required prior to its analysis. We successfully tested a freeze-drying pre-concentration method showing no associated isotope fractionation up to concentration factors of 500 and 50 for glyphosate and AMPA, respectively.

CONCLUSIONS

We demonstrated, for the first time, the feasibility of measuring the δ¹³ C values of glyphosate and AMPA in natural surface waters with contrasted hydrofacies (calcium carbonate and silicate types). This opens new fields in pesticide research, especially on the characterization of processes that control their degradation and the production of their secondary byproducts.

Ecotoxicology of Glyphosate, Its Formulants, and Environmental Degradation Products

The chemical and biological properties of glyphosate are key to understanding its fate in the environment and potential risks to non-target organisms. Glyphosate is polar and water soluble and therefore does not bioaccumulate, biomagnify, or accumulate to high levels in the environment. It sorbs strongly to particles in soil and sediments and this reduces bioavailability so that exposures to non-target organisms in the environment are acute and decrease with half-lives in the order of hours to a few days. The target site for glyphosate is not known to be expressed in animals, which reduces the probability of toxicity and small risks. Technical glyphosate (acid or salts) is of low to moderate toxicity; however, when mixed with some formulants such as polyoxyethylene amines (POEAs), toxicity to aquatic animals increases about 15-fold on average. However, glyphosate and the formulants have different fates in the environment and they do not necessarily co-occur. Therefore, toxicity tests on formulated products in scenarios where they would not be used are unrealistic and of limited use for assessment of risk. Concentrations of glyphosate in surface water are generally low with minimal risk to aquatic organisms, including plants. Toxicity and risks to non-target terrestrial organisms other than plants treated directly are low and risks to terrestrial invertebrates and microbial processes in soil are very small. Formulations containing POEAs are not labeled for use over water but, because POEA rapidly partitions into sediment, risks to aquatic organisms from accidental over-sprays are reduced in shallow water bodies. We conclude that use of formulations of glyphosate under good agricultural practices presents a de minimis risk of direct and indirect adverse effects in non-target organisms.

Assessment of pesticide inputs into surface waters by agricultural and urban sources - A case study in the Querne/Weida catchment, central Germany

Pesticide inputs into surface waters may cause harmful effects on aquatic life communities and substantially contribute to environmental pollution. The present study aimed at evaluating the input pathways in the Querne/Weida catchment (central Germany) to efficiently target mitigation measures of pesticide losses. Relevant pesticide substances were measured in surface waters in agricultural and urban surroundings and in soil samples within the catchment area. Pesticides application data from farmers were analyzed. Additionally, batch tests were performed to determine sorption and degradation of relevant pesticides for site specific soil properties. Frequency of detection, number of pesticides and maximum concentrations were much higher in the surface water samples in mainly urban surroundings compared to those in agricultural surrounding. The most frequently detected substances were glyphosate, AMPA, diflufenican and tebuconazole in surface water samples and diflufenican, boscalid, tebuconazole and epoxiconazole in the topsoil samples. Glyphosate and AMPA contributed to the highest concentrations in surface water samples (max. 58 μg L^-1) and soil samples (max. 0.19 mg kg^-1). In most cases, pesticide detections in surface water and soil were not consistent with application data from farmers, indicating that urban sources may affect water quality in the catchment area substantially. However, it was observed that pesticide substances remain in the soil over a long time supported by sorption on the soil matrix. Therefore, delayed inputs into surface waters could be suspected. For the implementation of reduction measures, both urban and agricultural sources should be considered. Novel findings of the study: pesticide detections were not consistent with application data from farmers, urban sources contributed substantially to pesticide pollution of surface waters.