Age matters: Submersion time shapes community composition in biofilm exposed to the herbicide glyphosate

New research has shown that exposure to the common herbicide glyphosate does not seem to impact the community composition of biofilms. Rather, microbial biofilm communities seem to be more influenced by submersion time than any other factor.

Glyphosate, the active ingredient in the commercial formulation Roundup®, is currently the most widely used herbicide in the world. Since it is at high risk of being ingested, the International Agency for Research on Cancer of the World Health Organization, stated in 2015 that glyphosate is “probably carcinogenic to humans.” This status raised serious concerns on a global scale and was largely disputed.

Read this open access paper on the FACETS website.

Health Canada stated in April 2017 that “when used according to the label, products containing glyphosate are not a concern to human health and the environment”. Since the Pesticides Re-evaluation Program only reviews registered pesticides every 15 years, the use and sale of products containing glyphosate is authorized in Canada until 2032. With its controversial legislation, this herbicide raises serious concerns at local and global scales, urging the need for extensive ecotoxicological studies.

Glyphosate-based herbicides are sprayed on food and feed crops during cultivation and are thus subject to leaching to streams and rivers. In aquatic ecosystems, periphytic biofilms, a gelatinous assemblage of bacteria, fungi, and algae found on submerged plants, form the base of many food webs and are often the first communities to be in direct contact with herbicidal runoff. While some cyanobacteria are known to degrade glyphosate and use it as a phosphorus source, effects on the rest of periphytic communities are unknown.

This study is the first one conducted in temperate latitudes on the effects of glyphosate on periphytic biofilms. Artificial substrates colonized by periphytic biofilms at different colonization stages (2 months, 1 year, and 20 years) were exposed to environmental levels of glyphosate. To our knowledge, this is the first study that uses such contrasting submersion periods. These biofilms differed in thicknesses and presumably in community structure; it was expected that they would respond differently to external stressors.

Results showed that submersion period was the only significant contributor to community structure. However, the glyphosate-resistant Cyanobacteria Anabaena was found to be favoured by the use of glyphosate. This freshwater Cyanobacteria commonly forms toxic blooms, raising concern regarding the use of glyphosate. In fact, some strains are known to produce hepatotoxins and neurotoxins — chemicals that target the liver and brain — posing a serious health hazard for wildlife and for humans.

This highlights that some effects might be detected at a population scale, but not at a community scale. This study therefore provides an interesting snapshot of the biological processes related to periphytic biofilms’ exposure to environmental concentrations of glyphosate. As this herbicide is currently of international concern, it is imperative to contribute to the advancement of knowledge about its effects.

Read the full paper — Age matters: Submersion period shapes community composition of lake biofilms under glyphosate stress by Melissa Khadra, Dolors Planas, Catherine Girard and Marc Amyot.