Abstract
The phosphonate herbicide glyphosate, which is the active ingredient in the commercial formulation Roundup®, is currently the most globally used herbicide. In aquatic ecosystems, periphytic biofilms, or periphyton, are at the base of food webs and are often the first communities to be in direct contact with runoff. Microcosm experiments were conducted to assess the effects of a pulse exposure of glyphosate on community composition and chlorophyll a concentrations of lake biofilms at different colonization stages (2 months, 1 year, and 20 years). This is the first study that uses such contrasting submersion periods. Biofilms were exposed to either environmental levels of pure analytical grade glyphosate (6 μg/L, 65 μg/L, and 600 μg/L) or to corresponding phosphorus concentrations. Community composition was determined by deep sequencing of the 18S and 16S rRNA genes to target eukaryotes and cyanobacteria, respectively. The results showed that submersion period was the only significant contributor to community structure. However, at the taxon level, the potentially toxic genus Anabaena was found to increase in relative abundance. We also observed that glyphosate releases phosphorus into the surrounding water, but not in a bioavailable form. The results of this study indicate that environmental concentrations of glyphosate do not seem to impact the community composition or metabolism of lake biofilms under pulse event conditions.
Highlights
NOTE – Pour connaître les conditions d’opération des différentes composantes de l’appareil, veuillez consulter le document de référence approprié dans la documentation qualité de la division de chimie organique
Protocole pour la validation d’une méthode d’analyse en chimie, DR-12-VMC, Ministère du Développement durable, de l’Environnement et des Parcs du Québec, Édition courante
Summary
La popularité grandissante de l’utilisation de glyphosate est attribuable à sa rapidité d’infiltration et de déplacement à l’intérieur de la plante, sa grande solubilité dans l’eau, sa faible persistance dans le sol et une faible toxicité pour les mammifères. Après la séparation chromatographique du glyphosate et de l’AMPA, le glyphosate seul est hydrolysé avec une solution d’hypochlorite de sodium. L’amine primaire ainsi formée par l’hydrolyse du glyphosate et l’AMPA réagissent avec l’OPA-thiofluor pour former des composés fluorescents qui sont détectés à l’aide d’un fluorimètre. NOTE – Une trop grande concentration de la solution d’hypochlorite de sodium entraînera une perte de sensibilité pour l’AMPA. Les concentrations de glyphosate et d’AMPA contenues dans l’échantillon sont calculées à l’aide d’une courbe d’étalonnage linéaire obtenue à partir de solutions étalons.
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