Effects of the Herbicide Roundup on Freshwater Microbial Communities: A Mesocosm Study

Abstract

The impact of the widely used herbicide glyphosate has been mainly studied in terrestrial weed control, laboratory bioassays, and field studies focusing on invertebrates, amphibians, and fishes. Despite the importance of phytoplankton and periphyton communities at the base of the aquatic food webs, fewer studies have investigated the effects of glyphosate on freshwater microbial assemblages. We assessed the effect of the commercial formulation Roundup using artificial earthen mesocosms. The herbicide was added at three doses: a control (without Roundup) and two treatments of 6 and 12 mg/L of the active ingredient (glyphosate). Estimates of the dissipation rate (k) were similar in the two treatments (half-lives of 5.77 and 7.37 d, respectively). The only two physicochemical parameters showing statistically significant differences between treatments and controls were the downward vertical spectral attenuation coefficient kd(lambda), where lambda is wavelength, and total phosphorus concentration (TP). At the end of the experiment, the treated mesocosms showed a significant increase in the ratio kd(490 nm)/k(d)(550 nm) and an eightfold increase in TP. Roundup affected the structure of phytoplankton and periphyton assemblages. Total micro- and nano-phytoplankton decreased in abundance in treated mesocosms. In contrast, the abundance of picocyanobacteria increased by a factor of about 40. Primary production also increased in treated mesocosms (roughly by a factor of two). Similar patterns were observed in the periphytic assemblages, which showed an increased proportion of dead: live individuals and increased abundances of cyanobacteria (about 4.5-fold). Interestingly, the observed changes in the microbial assemblages were captured by the analysis of the pigment composition of the phytoplankton, the phytoplankton absorption spectra, and the analysis of the optical properties of the water. The observed changes in the structure of the microbial assemblages are more consistent with a direct toxicological effect of glyphosate rather than an indirect effect mediated by phosphorus enrichment.

Herbicide Contamination of Freshwater Ecosystems: Impact on Microbial Communities

“…In addition they showed that in periphyton communities Roundup produced a long-term shift in the typology and functioning of contaminated mesocosms, which was consistent with data available from natural lakes in the Argentine Pampas. Another recent paper by Pérez et al (2007) has also demonstrated an impact of Roundup on the structure of the phytoplankton and periphyton communities, and more particularly a decrease in the total micro-and nanophytoplankton and an increase in picocyanobacteria. Moreover, they have shown that these changes are more likely to be due to a direct toxic effect of glyphosate rather than to an indirect effect via a phosphorus enrichment of the streams linked to the degradation of this compound.…”

Effects of Herbicide Glyphosate and Glyphosate-Based Formulations on Aquatic Ecosystems

“…Even if these two contributions assessed herbicide effects in worst case scenarios, glyphosate concentration at the end of the experiments (11 and 14 days respectively), were around 2 mg a.i./L and effects were still clearly observed. At day 11, significant differences were observed in chemical and biological variables (Pérez et al, 2007). For example, we observed changes in phytoplankton assemblage fractions, with a reduction of micro and nanophytoplankton densities (2.5 folds) and a concomitant increase of picocyanobacteria (PICY) densities (40 folds) accompanied by an increase of primary production.…”

“…Comparable results were obtained by Pesce et al (2009), reporting changes in riverine algal communities exposed to about 10 μg/L of glyphosate alone, in a microcosms experiment. In addition, mesocosms studies showed remarkable results with a single pulse application of Roundup ® at concentrations of 6 and 8 mg a.i./L (Pérez et al, 2007;Vera et al, 2010). Even if these two contributions assessed herbicide effects in worst case scenarios, glyphosate concentration at the end of the experiments (11 and 14 days respectively), were around 2 mg a.i./L and effects were still clearly observed.…”

“…In natural waters, glyphosate dissipate rapidly (half lives < 4 days) being removed from water due to adsorption to suspended particulates followed by subsequent sedimentation and or biodegradation. However, longer half lives were reported in hard waters, where glyphosate residues could be measured after 11 days post application (Pérez et al, 2007). Edwards et al (1980) reported important glyphosate concentrations in runoff from natural rainfall following early springtime treatments in no-tillage agriculture soils.…”

Glifosato e ácido aminometilfosfônico: desenvolvimento de metodologias de análise por injeção sequencial e investigação sobre processos adsortivos e fisiológicos de interesse ambiental

“…Estudos que acompanham a introdução do glifosato a sistemas biológicos simples, como um cultivo unialgal, ou a um sistema complexo, do tipo mesocosmos, o qual contém produtores, herbívoros e predadores, possibilitam a compreensão dos efeitos de herbicidas tanto na fisiologia do vegetal quanto nas cascatas tróficas nas quais estão envolvidas as plantas afetadas (Relyea e Yurewicz, 2002, Relyea, 2005Perez et al, 2007 …”