Effect of a glyphosate formulation on freshwater plankton: A community combined metric approach

Aim: The aim of this study was to experimentally assess the effects of glyphosate formulation on plankton composition by using different community parameters through a mesocosm experiment. Methodology: A 600 l mesocosm experiment was performed for 7 days, including a control (without glyphosate) and two concentrations of glyphosate. Results: Glyphosate caused a significant decrease in cladoceran density and a significant increase in rotifer, Chlorophyceae, and Euglenophyceae densities. In addition, zooplankton size diversity as well as microalgal evenness diminished. Interpretation: The decrease in cladoceran density may have benefited rotifers since they are less competitive for food resources. Moreover, the decrease in cladoceran foraging pressure over Chlorophyceae and Euglenophyceae may have benefited them. The different tolerances and competitiveness within the plankton components make the structure of this community a good indicator of environmental disturbance.

Eco-friendly surfactants in glyphosate formulation

Weeds affect various crops worldwide, causing low yields and, therefore, significant economic losses. These losses can be minimized by the use of herbicides such as glyphosate. However, the efficiency of glyphosate depends on the type of agrochemical formulations. The most widely used surfactant is polyethoxylated tallow amine. Nevertheless, the disadvantage of these compounds is that their toxicity is greater than that of glyphosate itself. Thus, this study aimed to develop an environmentally-friendly combination of surfactants that can increase the performance of glyphosate compared to other currently used formulations. Saponin (S) is environmentally friendly and has a unique ability to go through the waxy cuticle of the weed leaf. However, its interfacial properties are very poor. In contrast, the alkyl glucoside (AG) mixture has shown excellent interfacial properties, being an environmentally safe surfactant, but cannot pass through the cuticle. In the present study, we mixed both surfactants. Two formulations were made with 20% (F1) and 2% (F2) of S with 4% AG. To verify the usefulness of our formulations, they were compared against a commercial product. The results showed that the commercial product had better CMC 0.3±0.1% and pC20 1.155±0.099 than our formulations F1 and F2. Formulations F1 and F2 showed better gCMC than the commercial product 36.5±4.1 mN/m and 30.9±1.4 mN/m, respectively. Field tests showed that F2 was more effective than the commercial product in eliminating weeds at the end of the test at 30 days. Our results allowed confirming that the use of saponin improves the efficiency of glyphosate. The work showed that structures similar to cyclopentaneperhydrophenanthrene are very effective for introducing drugs into plants through the leaves. This is an advance in general and in particular for the increase of the yield in certain crops.

Inflammatory, Oxidative Stress, and Apoptosis Effects in Zebrafish Larvae after Rapid Exposure to a Commercial Glyphosate Formulation

Glyphosate-based herbicides (GBH) are the most used herbicides in the world, carrying potentially adverse consequences to the environment and non-target species due to their massive and inadequate use. This study aimed to evaluate the effects of acute exposure to a commercial formulation of glyphosate, Roundup® Flex (RF), at environmentally relevant and higher concentrations in zebrafish larvae through the assessment of the inflammatory, oxidative stress and cell death response. Transgenic Tg(mpxGFP)i114 and wild-type (WT) zebrafish larvae (72 h post-fertilisation) were exposed to 1, 5, and 10 µg mL−1 of RF (based on the active ingredient concentration) for 4 h 30 min. A concentration of 2.5 µg mL−1 CuSO4 was used as a positive control. Copper sulphate exposure showed effectiveness in enhancing the inflammatory profile by increasing the number of neutrophils, nitric oxide (NO) levels, reactive oxygen species (ROS), and cell death. None of the RF concentrations tested showed changes in the number of neutrophils and NO. However, the concentration of 10 µg a.i. mL−1 was able to induce an increase in ROS levels and cell death. The activity of antioxidant enzymes (superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GPx)), the biotransformation activity, the levels of reduced (GSH) and oxidised (GSSG) glutathione, lipid peroxidation (LPO), lactate dehydrogenase (LDH), and acetylcholinesterase (AChE) were similar among groups. Overall, the evidence may suggest toxicological effects are dependent on the concentration of RF, although at concentrations that are not routinely detected in the environment. Additional studies are needed to better understand the underlying molecular mechanisms of this formulation.

Toxicity of glyphosate-based isopropylamine salt and polyethoxylated tallow amine formulations on juvenile Clarias gariepinus

The formulation of glyphosate composed of Isopropylamine salt and Polyethoxylated tallow Amine (Clearweed) is widely used as herbicide to control weeds both in the terrestrial and aquatic environments. A static bioassay was conducted to examine toxicity of this formulation on juvenile African catfish (Clarias gariepinus). Catfish juvenile (mean weight 27.97±0.03g) were exposed to glyphosate at concentrations of 0.00mg/l (control), 5.00, 7.50, 10.00, 12.50 and 15.00mg/l. Each concentration was treated in triplicate and the exposure period lasted for 96 hrs. Mortality rates and physico-chemical parameters of water were monitored. Results revealed that fish mortality increased with increasing concentration of glyphosate and time of exposure. The median lethal concentration (96-hr LC50) value was 8.88mg/l with the upper and lower limits of 9.10mg/l and 7.75mg/l respectively. Behavioural changes observed the treated fish included: erratic swimming, jerky movement, increased opercula and tail movements, gulping of air, lost of balance and consciousness, cessation of opercula and tail movement signifying eventual death. Water quality parameters increased significantly (p<0.05) with extract concentration except dissolve oxygen levels which reduced (p<0.05). However, all values reported were within the permissible limits of the Federal Ministry of Environment (FMEnv) for water samples. The results of this study indicated that glyphosate formulation has toxic effects on catfish. Thus, the herbicide should be cautiously used to avoid ecotoxicological hazards particularly on non-target organisms.

Mixtures between glyphosate formulations and ACCase-inhibiting herbicides in the control of Chloris elata

Chloris elata is an important weed for grain and sugarcane crops. In addition to its aggressiveness, it may show resistance to glyphosate herbicide. In this context, the aim of this study was to assess the effectiveness of glyphosate formulations, isolated or in association with ACCase inhibitors, in controlling C. elata (putatively resistant to glyphosate) at different developmental stages. Four experiments were conducted in a completely randomized design. Treatments consisted of glyphosate application under different formulations with ACCase inhibitors, isolated or in mixtures. Applications were carried out at the stages of four fully expanded leaves in Experiment I, four tillers in Experiment II, and at regrowth of the four-tiller plants in Experiments III and IV. Applications of glyphosate isopropylamine salt associated with sethoxydim or clethodim showed to be among the best treatments in Experiments I, II, and III, presenting control scores equal to or greater than 90%. However, not even these treatments could provide successful control in Experiment IV. Moreover, and regardless of the formulation, isolated glyphosate, showed 85% (Experiment III) and 50% (Experiment IV) maximum controls. Associations between glyphosate and ACCase-inhibiting herbicides showed to be effective in controlling C. elata, especially at early developmental stages. In general, isolated herbicides provided lower percentages of control, as well as higher values of dry matter. Sole herbicide applications were not effective in controlling C. elata (putatively resistant to glyphosate), regardless of the developmental stage. Highlights: Mixtures between glyphosate and ACCase-inhibiting have been shown to be effective in C. elata control, especially in the early development stages. Isolated herbicide applications were not effective in controlling C. elata, regardless of the development stage. Mixtures between glyphosate and ACCase-inhibiting is more important in the control than the glyphosate formulation or ACCase-inhibiting used.

Ecotoxicological Studies on the Effect of Roundup® (Glyphosate Formulation) on Marine Benthic Microalgae

Glyphosate is a very effective herbicide and the main active ingredient in Roundup®—the most extensively used herbicide in the world. Since glyphosate is highly water soluble it reaches water bodies easily in surface water runoff. This prompted us to undertake an experiment to evaluate the effects of glyphosate in Roundup® on natural communities of marine microphytobenthos. Microphytobenthos communities were obtained from the environment, and after transporting them to the laboratory and acclimatizing them, they were tested under controlled conditions. Changes in microphytobenthos composition and structure and the deteriorating condition of the cells of community-forming organisms (assessed by analyzing changes in chloroplast shape) were used to assess the impact of Roundup® on endpoints. The tests indicated that microphytobenthic communities were relatively resistant to herbicide. The species richness of the communities probably enabled them to rebuild effectively. Sensitive species were replaced by those more tolerant of glyphosate. Only at the highest glyphosate concentration (8.5 g·dm−3) tested was a strong negative effect noted that limited community abundance and eliminated some of the organisms. The dominant diatoms in the communities were replaced by intensively developing cyanobacteria, which ultimately comprised nearly 60% of all the cells observed in the communities.

Ammonium Sulfate Improves the Efficacy of Glyphosate on South African Lovegrass (Eragrostis plana) Under Water Stress

South African lovegrass (Eragrostis plana Nees) is the most important weed of native pastures in southern Brazil. Management options are limited under water stress conditions and glyphosate has been the main tool for control. This study compared four salts of glyphosate applied at three growth stages, and determined the glyphosate tolerance level. In addition, the performance of ammonium sulfate (AMS) under two soil moisture conditions (50% and 100% of water holding capacity), and the effect of AMS on absorption and translocation of radiolabeled 14C-glyphosate were evaluated. The potassium salt of glyphosate had the fastest activity across growth stages of E. plana, which is more vulnerable to glyphosate at panicle initiation stage. Isopropylamine salt was the slowest-acting glyphosate formulation. Younger plants were typically more easily controlled than older plants at full tillering stage. The addition of AMS increased the level of control of drought-stressed E. plana, compared to glyphosate alone, by increasing translocation out of the treated leaf and consequently increasing the concentration of glyphosate in the primary culm. This data can be used to plan an effective management program for E. plana considering the developmental stage of desired pasture grass species.

Avoidance behavior of juvenile common toads (Bufo bufo) in response to surface contamination by different pesticides

Most agricultural soils are expected to be contaminated with agricultural chemicals. As the exposure to pesticides can have adverse effects on non-target organisms, avoiding contaminated areas would be advantageous on an individual level, but could lead to a chemical landscape fragmentation with disadvantages on the metapopulation level. We investigated the avoidance behavior of juvenile common toads (Bufo bufo) in response to seven pesticide formulations commonly used in German vineyards. We used test arenas filled with silica sand and oversprayed half of each with different pesticide formulations. We placed a toad in the middle of an arena, filmed its behavior over 24 hours, calculated the proportion of time a toad spent on the contaminated side and compared it to a random side choice. We found evidence for the avoidance of the folpet formulation Folpan® 500 SC, the metrafenone formulation Vivando® and the glyphosate formulation Taifun® forte at maximum recommended field rates for vine and a trend for avoidance of Wettable Sulphur Stulln (sulphur). No avoidance was observed when testing Folpan® 80 WDG (folpet), Funguran® progress (copper hydroxide), SpinTorTM (spinosad), or 10% of the maximum field rate of any formulation tested. In the choice-tests in which we observed an avoidance, toads also showed higher activity on the contaminated side of the arena. As video analysis with tracking software is not always feasible, we further tested the effect of reducing the sampling interval for manual data analyses. We showed that one data point every 15 or 60 minutes results in a risk of overlooking a weak avoidance behavior, but still allows to verify the absence/presence of an avoidance for six out of seven formulations. Our findings are important for an upcoming pesticide risk assessment for amphibians and could be a template for future standardized tests.

Can Control of Glyphosate Susceptible and Resistant Conyza sumatrensis Populations Be Dependent on the Herbicide Formulation or Adjuvants?

In this work, we studied the effect of three glyphosate formulations (isopropylamine, ammonium and potassium salts) and two non-ionic adjuvants on the resistance response of two resistant (R1, R2) and one susceptible population of the highly invasive Asteraceae, Conyza sumatrensis, from Southern France vineyards. Only in R1, an amino acid substitution (Pro106Thr) was found in the enzyme 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS). The two adjuvants, in a similar fashion, significantly reduced GR50 values for every population and glyphosate formulation. Without adjuvants, glyphosate as potassium salt was the only formulation able to significantly reduce the GR50 values of every population. For every population, the two adjuvants improved, indistinguishably, leaf retention of the herbicidal solution and the potassium salt formulation led to the highest retention, both with and without the adjuvant added. Uptake responses paralleled those of retention and adjuvant addition was more effective in increasing foliar uptake of the lower performing formulations (isopropylamine and ammonium salts). The allocation pattern of glyphosate among plant compartments was only dependent on population, with R2 retaining most glyphosate in the treated leaf, clearly suggesting the occurrence of a Non-Target Site Resistance (NTSR) mechanism. Results indicate that control of weed populations possessing NTSR mechanisms of resistance to glyphosate may be improved through adequate selection of formulation and adjuvant use.