Assessment of the potential toxicity of glyphosate-based herbicides on the photosynthesis ofNitella microcarpavar.wrightii(Charophyceae)

Abstract

Although macroalgae are considered one of the most important primary producers in streams, to our knowledge there has been no research on the effects of herbicides on these organisms. Such studies are crucial for improving our understanding of the impact of these substances on stream ecology. In this study, we assess the effects of technical-grade glyphosate, Roundup and aminomethylphosphonic acid (AMPA; the main degradation product of glyphosate) on the photosynthetic rate, dark respiration rate and chlorophyll a content of Nitella microcarpa var. wrightii, a green algae found worldwide. Three concentrations of technical-grade glyphosate and Roundup were tested (0.28, 3.5 and 6 mg l À1 ), while for AMPA only one concentration was evaluated (0.03 mg l À1 ). Our results indicate that glyphosate has a stronger inhibitory effect on photosynthetic rate when applied in association with a surfactant (Roundup). These effects are related both to the concentration of the active ingredient and to exposure time. On the other hand, treatment with AMPA had a stimulatory effect on the photosynthetic rate, which may be associated with an increased supply of phosphorus available to the algae from the AMPA degradation process. From an ecological perspective, our results show that the ecological distribution of N. microcarpa var. wrightii, in terms of both spatial and temporal scales, can be affected by glyphosate-based herbicides in streams.

Effect of glyphosate-based herbicides on the photosynthetic responses of the macrophyte Egeria densa Planch. from topical lotic ecosystems

“…The nominal experimental concentrations of Roundup ® were calculated based on acid equivalent (a.e.) values (360 g/L) so that the preparation of each concentration took into account the following dilutions (according to Oliveira et al, 2016): First, to obtain an initial concentration of 0.28 mg/L, 0.77 μL of Roundup ® was added to 1 L of sterilized Bold's basal medium. Then, to obtain an initial concentration of 3.5 mg/L, 9.7 μL of Roundup ® was added to 1 L of sterilized Bold's basal medium.…”

“…Finally, to obtain an initial concentration of 6 mg/L, 16.6 μL of Roundup ® was added to 1 L of sterilized Bold's basal medium. Considering the nominal experimental concentration of AMPA, to obtain a concentration of 0.03 mg/L, 1 mg of AMPA (≥ 99 % purity, CAS # 1066-51-9) was initially added to 1 L of sterilized distilled water, and then a 30 mL aliquot of this 1 % aqueous AMPA solution was added to 1 L of sterilized Bold's basal medium (Oliveira et al, 2016). In addition, for each treatment tested, a control group containing sterilized Bold's basal medium without herbicide (0 mg/L) was simultaneously evaluated.…”

“…The procedures to expose E. densa samples to Roundup ® and AMPA were carried out based on a semi-static test model with the analysis of the photosynthetic responses performed on the seventh day (T7) after exposure to herbicides and the renewal of the experimental media on the third and fifth days to prevent the loss of nutrients and active ingredient (Nešković et al, 1996;Oliveira et al, 2016).…”

“…Glyphosate is a non-selective herbicide absorbed by plants through leaves that competitively inhibits the enzyme 5-enolpyruvylshikimate-3-phosphate synthase (EPSPs) in the synthesis of aromatic amino acids (Forlani et al, 2008;Oliveira et al, 2016). In practice, the exposure of plants to glyphosate leads to the inhibition of the action of EPSPs in the metabolic pathway of aromatic amino acids, consequently causing a decrease in the production of certain amino acids indispensable for plant metabolism, such as phenylalanine, tyrosine, and tryptophan (Sáenz & Di Marzio, 2009).…”

Examining German Media Coverage of the Re-Evaluation of Glyphosate

“…Glyphosate was initially considered an effective and yet environmentally friendly herbicide [15] with relatively little ecological and toxicological side effects [16]. However, a review [17] highlights numerous studies that demonstrate negative effects of glyphosate on organisms, unicellular [18] and multicellular [19], invertebrates [20], and vertebrates [21,22]. While the active ingredient adheres to soil particles, its metabolite aminophosphonic acid (AMPA) is more mobile [6].…”