Differential impact of Limnoperna fortunei-herbicide interaction between Roundup Max® and glyphosate on freshwater microscopic communities

Abstract

Multiple anthropogenic stressors act simultaneously on the environment, with consequences different from those caused by single-stressor exposure. We investigated how the combination of the invasive mussel Limnoperna fortunei and a widely applied herbicide, Roundup Max®, affected freshwater microscopic communities and water quality. Further, we compared these results with those induced by the combination of the mussel and technical-grade glyphosate. We carried out a 34-day experiment in outdoor mesocosms, applying the following six treatments: 6 mg L(-1) of technical-grade glyphosate (G), the equivalent concentration of glyphosate in Roundup Max® (R), 100 mussels (M), the combination of mussels and herbicide either in the technical-grade or formulated form (MG and MR, respectively), and control (C). Herbicides significantly increased total phosphorus in water; R and MR showed greater initial total nitrogen and ammonium. R increased picoplankton abundance and caused an eightfold increase in phytoplankton, with high turbidity values; G had a lower effect on these variables. Herbicide-mussel combination induced an accelerated dissipation of glyphosate in water (MG 6.36 ± 0.83 mg G g DW(-1) day(-1) and MR 5.16 ± 1.26 mg G g DW(-1) day(-1)). A synergistic effect on ammonium was observed in MR but not in MG. MR and MG had an antagonistic effect on phytoplankton, which showed a drastic reduction due to grazing, as revealed by M. We provide evidence of differential effects of Roundup Max® and technical-grade glyphosate over water quality and microscopic communities, and in combination with mussels. However, in the combination of mussels and herbicides, mussels seem to play a leading role. In the presence of L. fortunei, the effects of higher nutrient availability provided by herbicides addition were counteracted by the filtration activity of mussels, which released nutrients, grazed on picoplankton and phytoplankton, and boosted the development of other primary producers, periphyton and metaphyton.

Effect of glyphosate on the growth, morphology, ultrastructure and metabolism of Scenedesmus vacuolatus

“…The analysis of initial glyphosate concentrations in the culture medium was carried out by HPLC-UV chromatography after a derivatization step with FMOC-Cl, as described in Gattás et al (2016). The limit of detection and quantification of the resulting procedure were 0.2 and 0.7 mg L −1 , respectively, and the percent variation coefficient was of 4.3%.…”

Comparative impact of two glyphosate-based formulations in interaction with Limnoperna fortunei on freshwater phytoplankton

“…It has been demonstrated that the joint effect of Limnoperna fortunei and glyphosate on the structure of freshwater microbial communities and water quality is different from the effect of each factor considered separately (Pizarro et al, 2015a). Gattás et al (2016) reported that L. fortunei seemed to be the most powerful driver of the interaction, which elicited different responses depending on whether it involved glyphosate or a commercial formulation (Roundup Max ® ). In this study another widely used glyphosate-based formulation, Glifosato Atanor ® , was included in the analyses.…”

“…In our study, the addition of Roundup Max ® and Glifosato Atanor ® caused rapid changes in water chemistry as indicated by the significant increase in ammonium concentration at Ti. In the case of Roundup Max ® , this may have been due to its active ingredient, which is a monoammonium salt of N-phosphonomethylglycine that dissociates in aqueous solution releasing ammonium (Gattás et al, 2016). The ammonium increase resulting from the addition of Glifosato Atanor ® would be explained by the formulation adjuvants of unknown specific composition because its active ingredient is a monopotassium salt of glyphosate (Giesy et al, 2000).…”

“…In addition, they reported that metaphyton was abundant in the treatments with glyphosate and mussels due to increased availability of nutrients and that both stressors acted synergistically on phosphate concentration, bacterioplankton abundance and water turbidity. Gattás et al (2016), who investigated the combined effect of L. fortunei plus acid glyphosate with that of L. fortunei plus Roundup Max ® on microbial communities in outdoor mesocosms, obtained different results according to the type of herbicide.…”

Freshwater periphyton response to technical-grade and two commercial formulations of glyphosate

“…Ecología Austral 29:020-027 grade glyphosate (Vera et al 2014). On the other hand, Gattás et al (2016) reported that Chlorophyceae and Desmidiaceae were favored by both Roundup Max ® and the active ingredient. In our study, both glyphosate-based formulations showed higher toxicity than the technical-grade glyphosate for Chlorophyta and Bacillariophyta.…”