Is Glyphosate wrecking aquatic life?

September 2013

Water lily.  CC Photo by Mahmood Al-Yousif on Flickr
At least three published reviews have declared glyphosate (active ingredient of Monsanto's 'Roundup') to be an ideal herbicide due to its specificity and acclaimed low toxicity to non-target organisms in the environment.

Indeed, a majority of short-term studies on the aquatic invertebrate, Daphnia magna, a commonly accepted model animal in environmental toxicity studies, has pronounced 'glyphosate' to have 'no adverse effect', to be 'non-toxic' or 'moderately toxic', or to have 'low toxicity'.

However, experiments over the decades since glyphosate was first marketed have demonstrated an unexplained variability in toxicity across several orders of magnitude.

Glyphosate is heavily used in agriculture, forestry, gardening and waterway management, from where it seeps into ground-water and drinking water. With the advent of 'Roundup Ready' GM monocultures, quickly followed by Roundup-resistant super-weeds, the quantity of glyphosate entering the ecosystem has increased exponentially.

In light of this, the scientific uncertainty attaching to experimental results which have proven unrepeatable as described above, is of concern, especially to ecologists.

Suspecting that there must be some uncontrolled variables in the glypohosate toxicity experiments which were affecting the outcomes, a Norwegian team of scientists investigated the cause of the discrepancies.

Their findings eliminated the possibility that the use of different clones of Daphnia magna could be causing the variations, but they did unearth some fundamental weaknesses in the materials and methods of previous studies.

One of these was the indiscriminate use of the common name 'glyphosate' to describe the substance being tested.

'Glyphosate' can exist in a number of chemical forms which have different solubilities in water, and 'glyphosate' formulated into different versions of 'Roundup' can have a variety of different adjuvants added. Solubility and adjuvants both have a profound effect on glyphosate penetration into cells, and therefore on its toxicity. Other experimental conditions, such as acidity, buffering and temperature, are also important in rendering glyphosate more, or less, toxic.

The concentration of active glyphosate tested will also change depending on the actual format used. For example, one study in the 1980s expressed the concentration of the harmful dose of Roundup in terms of its whole formulation including the water content.

The second weakness has been the use of 'death' as the only significant end-point for toxicity studies.

What the Norwegian scientists recorded were glyphosate and Roundup effects on a full range of life-history traits i.e. survival, growth, fecundity, abortion rates, juvenile body size and age-effects. They found adverse signs in all these parameters at a glyphosate concentration around the US and Canadian environmental guideline contamination maximum, including “complete reproductive failure” and signs of increased sensitivity in younger Daphnia.

Actual readings of glyphosate contamination in streams draining Roundup Ready soya fields in Argentina found levels of up to ten times these environmental guidelines.

The European Commission working document on glyphosate (EZ2002), which forms the basis for European regulation in the context of health and the environment, uses toxicity values obtained in 1981. These are clearly derived from a form of glyphosate which has low water-solubility, and therefore low toxicity. Measurements of these effects on Daphnia were then extrapolated into a general value for acute toxicity of glyphosate in all aquatic invertebrates. Thus glyphosate became officially “harmless”.

In summary, the authors conclude that according to their experimental work plus literature reviews, the published toxic levels for glyphosate are not representative. They continue “The classification of glyphosate as “practically non-toxic to aquatic invertebrates is based on these non-representative values”.

It seems the low toxicity myth has proved tenacious, being extensively referred to in the literature and finding its way into regulatory documents.

As the Norwegian scientists politely suggest, the safety classification of glyphosate “needs to be adjusted”.


Sadly, this story is one of decades of bad science: the material in experiments was not specified and not comparable, the observed variation was either ignored or used as a basis for cherry-picking which results to accept, and an entirely unjustifiable extrapolation was made from a single animal to the whole of its ecosystem.

The most shocking thing is how long it has taken, and how many regulatory bodies have looked at the studies, before anyone noticed anything amiss.

Damage to aquatic life is just another way in which glyphosate is wrecking the environment.

  • Marek Cuhra et al., 2013, Clone- and age-dependent toxicity of a glyphosate commercial formulation and its active ingredient in Daphnia magna, Ecotoxicology 22

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