A newly published peer-reviewed study from Brazil has found that even legal levels of glyphosate-based herbicides have an impact on a common freshwater algae’s photosynthesis, dark respiration and chlorophyll levels, leading to global concerns over damage to freshwater aquatic systems.

An article in the current issue of the journal Phycologia looks at the Brazilian study that examined the effects of glyphosate-based herbicides on a type of green macroalga that is common in streams around the world. The researchers anticipated that the macroalgae would be sensitive to the chemicals, which would affect their photosynthesis, chlorophyll levels, and respiration. According to Professor David Garbary, the Editor of Phycologia, “This paper provides an important contribution to our knowledge of the environmental toxicology of glyphosate-based herbicides in freshwater aquatic systems.”

Glyphosate-based herbicides are the most widely used weed killers worldwide. Large amounts run off into streams, exposing the freshwater ecosystems to the chemicals. Several studies have found glyphosate contamination in U.S., Canadian, French, Argentinean, and other waters; however, the authors of the Brazilian study found no research had been done on the effects of these herbicides on macroalgae. Macroalgae are ideal for monitoring the health and clarity of rapidly moving fresh water. In streams, they are some of the most important organisms when it comes to cycling nutrients and increasing plankton.

The Brazilian study tested several concentrations of technical-grade glyphosate, Roundup® weed killer, and aminomethylphosphonic acid (AMPA) to find out how they affect Nitella microcarpa var. wrightii, a green algae that is found worldwide. Samples were collected from a stream in southwestern Brazil.