Even though glyphosate is used to control weeds in agricultural fields, the world's most commonly used weedkiller has also been detected in streams, rivers and other aquatic systems worldwide due to runoff.

New study examines glyphosate's effects on freshwater aquatic systems in Brazil.

As we learn more and more about the potential environmental risks of glyphosate runoff, in Brazil—where almost 188,000 tons of glyphosate was sold in 2013 alone—new research published in the peer-reviewed journal Phycologia found that all-important macroalgae is sensitive to glyphosate exposure, even at legal levels. According to the study, the herbicide can alter the photosynthesis, chlorophyll levels and respiration of these key freshwater organisms.

Macroalgae play a crucial role in aquatic systems. As a press release for the study pointed out, these organisms help monitor the health and clarity of rapidly moving fresh water. In streams, they cycle nutrients and help increase plankton.

For the study, the authors tested several concentrations of Monsanto's glyphosate-based Roundup and aminomethylphosphonic acid (AMPA; the main degradation product of glyphosate) on green algae samples collected from a stream in southwestern Brazil. The green algae tested, Nitella microcarpa var. wrightii, is commonly found in streams around the world.

As Sustainable Pulse reported from the study:

The authors found that glyphosate + surfactants (Roundup) strongly reduced algal photosynthesis. According to author Ciro Cesar Zanini Branco, "Such effects are related to the concentration of the active ingredient and also to the exposure time. These impacts were observed even at the concentration levels allowed by Brazilian regulations."

In contrast, AMPA boosted photosynthesis. Dark respiration, or respiration that occurs regardless of light, also increased with AMPA treatment. Finally, the current study found less chlorophyll when AMPA and certain amounts of solely glyphosate were applied."

"Clearly," as the press release stated, "the performance of the algae was affected by the herbicides."

"The form of the herbicide (glyphosate, glyphosate plus Roundup or AMPA) is crucial in determining the intensity of the effects, which means that algal productivity could shift visibly depending on the types of herbicides applied to agricultural land near a stream—even if farmers are using them legally," the release continued.

Significantly, the authors stressed, even legal concentrations of Roundup in Brazilian waters "may present significant environmental risks":

"One of the most dramatic findings of this study is that a significant reduction in photosynthetic rate of N. microcarpa var. wrightii was observed (−42.1 percent) even at the lowest Roundup concentration tested (0.28 mg l−1). Considering that 0.28 mg l−1 is the maximum concentration of this herbicide allowed by Brazilian law in water used for irrigation and animal consumption (National Environmental Council 2005) and the occurrence of glyphosate in the environment (Coupe et al. 2012; Majewski et al. 2014), this result suggests that even legal concentrations of Roundup in water bodies commonly used for these activities (e.g. low-order streams and small lakes) may present significant environmental risks."

Even though glyphosate contamination has been detected in the waters of the U.S., Canada, France, Argentina and other countries, the authors of the current study noted that there has been no prior research on the effects of glyphosate on macroalgae.

"This paper provides an important contribution to our knowledge of the environmental toxicology of glyphosate-based herbicides in freshwater aquatic systems," said Phycologia editor David Garbary.

Dr. Nathan Donley, a scientist at the Center for Biological Diversity, told EcoWatch that the Brazilian study "adds to the body of literature that glyphosate in combination with other ingredients can be more harmful than just glyphosate by itself."

Donley, who was not involved in the current study, observed that the environmental health risks of glyphosate merits attention.

"A lot of the recent focus on glyphosate has been on human cancer, but it's important to realize that this is not only a carcinogen but also a toxin that is harmful to our natural ecosystems," he said. The World Health Organization's International Agency for Research on Cancer linked glyphosate to cancer last year.

"Glyphosate is extremely toxic to plant life and these effects can have serious consequences for other organisms as well," he said. "We've been seeing glyphosate killing milkweed all over the country and having serious unintended consequences for the Monarch butterfly. It is still unknown how these effects on macroalgae could be effecting changes in stream ecosystems."

"The problem is that the [Environmental Protection Agency] is still stuck in this fairytale world where chemicals are encountered in isolation and that is not an accurate reflection of how exposure occurs. 'Inert' ingredients are not inert, they have activity and they can change the toxicity profile of the active ingredients and can also have toxicities themselves," Donley concluded.