Stronger effects of Roundup than its active ingredient glyphosate in damselfly larvae

Abstract

Pesticides are causing strong decreases in aquatic biodiversity at concentrations assumed safe by legislation. One reason for the failing risk assessment may be strong differences in the toxicity of the active ingredient of pesticides and their commercial formulations. Sublethal effects, especially those on behaviour, have been largely ignored in this context, yet can be equally important as lethal effects at the population and ecosystem levels. Here, we compared the toxicity of the herbicide Roundup and its active ingredient glyphosate on survival, but also on ecologically relevant sublethal traits (life history, behaviour and physiology) in damselfly larvae. Roundup was more toxic than glyphosate with negative effects on survival, behaviour and most of the physiological traits being present at lower concentrations (food intake, escape swimming speed) or even only present (survival, sugar and total energy content and muscle mass) following Roundup exposure. This confirms the toxicity of the surfactant POEA. Notably, also glyphosate was not harmless: a realistic concentration of 2mg/l resulted in reduced growth rate, escape swimming speed and fat content. Our results therefore indicate that the toxicity of Roundup cannot be fully attributed to its surfactant, thereby suggesting that also the new generation of glyphosate-based herbicides with other mixtures of surfactants likely will have adverse effects on non-target aquatic organisms. Ecotoxicological studies comparing the toxicity of active ingredients and their commercial formulations typically ignore behaviour while the here observed differential effects on behaviour likely will negatively impact damselfly populations. Our data highlight that risk assessment of pesticides ignoring sublethal effects may contribute to the negative effects of pesticides on aquatic biodiversity.

Re-registration Challenges of Glyphosate in the European Union

“…Roundup Express R and POEA were detected to exert toxicity on juveniles of the Pacific oyster Crassostrea gigas upon sub-chronic (35-day) exposure at concentrations of 0.1, 1 and 100 ng/ml (Mottier et al, 2013(Mottier et al, , 2014Séguin et al, 2017). Roundup Original R exerted lethal and sub-lethal effects on the widely distributed in dipteran freshwater nematoceran fly Chironomus xanthus with a 48 h LC 50 corresponding to glyphosate concentration of 251.5 mg/l, as well as reduced larval growth of and disturbed emergence of adults at lower concentrations (Ferreira-Junior et al, 2017), and it reduced the growth rate, the escape swimming speed and the fat storage also on the endangered damselfly Coenagrion pulchellum at a level corresponding to a glyphosate concentration of 2 mg/l, which is likely to lead to negatively influence fitness, mortality by predation and population dynamics (Janssens and Stoks, 2017). As in the latter test Roundup systematically resulted in 25-100% higher effects than glyphosate at equivalent concentrations, the enhanced effect was attributed to POEA.…”

Toxicological and Biochemical Investigation of certain Herbicides on Culex pipiens L. (Diptera: Culicidae) Mosquitoes under Laboratory Conditions

“…The LC50 of glyphosate alone and its Roundup formulation on Daphina magna Straus were 962 and 25.5 mg L-1 after 96 h of treatment [42]. Janssens and Stoks (2017) [43] found that the formulation of roundup had greater impacts on insects than their active ingredient alone.…”

Synergistic action of glyphosate on novel pesticides against Culex pipiens L. (Diptera: Culicidae) mosquitoes under laboratory conditions

“…Further, herbicide formulations contained some chemical additives such as surfactants that considered highly toxic on different aquatic animals and insects (Tu et al, 2001;Mohamed et al, 2016;Saba et al, 2018). Moreover, (Janssens and Stoks, 2017) revealed that the formulation of roundup was more toxic on insects than their active ingredient if tested alone. Certain herbicides such as Fluazifop-p-butyl and fenoxaprop-p-ethyl exhibited high toxicity against Culex pipiens larvae with LC50 values of 2.69 and 2.05 µg/ml after 24-h exposure, respectively (Mohamed et al, 2016).…”