Truth: So-called “safe” levels of Roundup may not be safe after all

Myth at a glance

It is often claimed that regulations protect us from unsafe pesticide exposures. But the effects on animals and humans of eating increased amounts of Roundup residues in GM Roundup Ready (RR) crops have not been investigated. On the contrary, since the introduction of GM RR crops, regulators have changed safety rules to allow higher levels of glyphosate residues into the food and feed chain. So people and animals that eat GM RR crops are eating potentially toxic herbicide residues.

The supposedly safe levels of glyphosate set by regulators have never been tested to find out if they really are safe to consume over the long term. Also, the safety limits were set for glyphosate alone, not the complete herbicide formulations as sold and used – yet many studies show that the formulations containing added ingredients (adjuvants) are more toxic than glyphosate alone.

Even glyphosate alone was found to cause toxic effects in vitro (laboratory non-animal studies) at a level permitted in drinking water in the EU and the US, though these findings would need to be confirmed in vivo (animal experiments).

GM crops have increased the use of glyphosate and thus people’s exposure to it, presenting a risk that has not been adequately considered in regulatory assessments.

GM herbicide-tolerant crops are designed to survive being sprayed with large doses of herbicide that would kill a non-GM crop. The most widely grown GM crop is Roundup Ready (RR) soy,1 the majority of which is grown in South America and is used for animal feed in intensive livestock operations in Europe and other industrialized countries. Inevitably, RR crops contain far higher levels of Roundup residues than have previously formed part of our diet.2

It is often claimed that regulations protect us from unsafe pesticide exposures. But in fact the effects on animals and humans of eating increased amounts of Roundup residues in GM RR crops have not been investigated. On the contrary, since the introduction of GM RR crops, regulators have changed safety rules to allow higher levels of glyphosate residues into the food and feed chain – without any experimental evidence to show that these higher levels of exposure are indeed safe.

For example, after the 1996 commercialization of GM RR soy, EU regulators raised the allowed maximum residue limit (MRL) for glyphosate in imported soy 200-fold, from 0.1 mg/kg to 20 mg/kg.3 The UK government said this was necessary to accommodate the new farm practice of using glyphosate as a desiccant to dry crops before harvest, making grains or beans easier to gather and store without rotting.3 This is no doubt true, but it also conveniently coincided with the introduction of RR soy.

Indeed, a 1994 report of the Joint FAO/WHO Meetings on Pesticide Residues (JMPR) indirectly admitted that GM soy was a factor in the need for the higher limit. The JMPR meeting appears to have been the source of the recommendation for the new higher residue limit. In its report, the JMPR recommended the higher limit of 20 mg/kg for soybeans. The JMPR said the change was needed not only due to glyphosate’s use as a desiccant before harvest, but also to accommodate “sequential application of glyphosate in the crop”.4 This practice is only possible with GM RR soy, as it would kill non-GM soy.

In a 1999 press interview, Malcolm Kane, who had just retired as head of food safety at UK supermarket chain Sainsbury’s, confirmed that the European regulators raised the residue limit to “satisfy the GM companies” and smooth the path for GM soy to enter the food and feed market. Kane added, “One does not need to be an activist or overtly anti-GM to point out that herbicide-resistant crops come at the price of containing significant chemical residues of the active chemical in the commercial weedkiller.”3

Recent analysis has found that GM RR plants can accumulate up to 100 mg/kg of glyphosate.5 Some animal feed plants are authorized by the international food standards body Codex Alimentarius to accumulate up to 500 mg/kg.6

How safe are “safe” levels?

The maximum residue limit (MRL) set by regulators for glyphosate in some food and feed crops in the EU is 20 mg/kg.7 The “acceptable daily intake” of glyphosate is set at 0.3 mg per kg of bodyweight per day (written as 0.3 mg/kg bw/d).8

Are these levels safe? There is strong reason for doubt. This is because:

  • These supposedly safe levels of glyphosate consumption have never been tested to find out if they really are safe to consume over the long term. Instead, the supposed safe levels are extrapolated from industry tests using very high, poisonous doses. This is not valid because some toxins, especially those that disrupt the hormonal system (endocrine disruptors) are known to be more toxic at low doses than higher doses, so safe levels cannot be extrapolated from effects at higher doses.9
  • The safety limits were set for glyphosate alone, not the complete herbicide formulations as sold and used (this limitation of the regulatory process applies to all pesticides in all countries worldwide). The complete formulations contain adjuvants, which have been shown to be toxic in themselves and to increase the toxicity of glyphosate to human cells in vitro (non-animal laboratory studies).10 Studies in rats carried out by independent scientists show that the complete formulations are toxic at levels deemed safe by regulators for the isolated ingredient glyphosate.11,12,13
  • In vitro studies in human cells show that glyphosate-based herbicide formulations are far more toxic than glyphosate alone. This principle was true for eight of nine pesticides tested – the formulations were up to 1,000 times more toxic.14 Thus safe levels set for glyphosate are not adequate for ensuring the safety of the formulations.
  • Feeding studies in pigs15 and rats16 directly comparing the toxicity of formulations with glyphosate alone found that the formulations were far more toxic.
  • Industry tests on glyphosate alone revealed toxic effects below the levels that regulators claimed showed no toxic effect – but these results were ignored or dismissed by regulators in setting the supposedly safe levels. Thus even the “safe” levels set for glyphosate are questionable.11
  • A study in Daphnia magna (a type of water flea often used as an experimental model for environmental toxicity) demonstrated that chronic exposure to glyphosate and a commercial formulation of Roundup resulted in reproductive problems, including reduced fertility and increased abortion rate, at environmental concentrations of 0.45-1.35 mg/l: that is, in some cases below accepted environmental tolerance limits set in the US (0.7 mg/l). A reduced body size of juveniles was observed at an exposure of 0.05 mg/l.17 The study authors commented that their findings were in sharp contrast to worldwide regulatory assumptions, which were strongly influenced by old studies by Monsanto claiming that glyphosate is virtually non-toxic in Daphnia magna.18
  • Glyphosate, its metabolite AMPA, and especially the commercial formulation Roundup have been found to be toxic in vitro, in some cases at extremely low levels.19,20,21 Roundup damages and kills human cells at levels below those used in agriculture22 and at residual levels to be expected in food and feed derived from Roundup-treated crops.19 Roundup is a potent endocrine disruptor, disturbing hormonal function in human cells vitro at concentrations up to 800 times lower than permitted levels in some food and feed crops.23

Levels of glyphosate found in GM soy are higher than those causing cancer cells to proliferate in vitro

In an in vitro study, glyphosate alone acted as an estrogen substitute in human hormone-dependent breast cancer cells, stimulating their growth at minute concentrations as low as 10(-12) M. The toxic effect peaked at the higher dose of 10(-9) M and then decreased at still higher concentrations.24 This is an example of a non-linear dose-response: the toxic effect did not increase in a straight line in proportion to the dose but instead decreased as the dose increased. This type of response is typical of endocrine disrupting chemicals (EDCs), chemicals that disturb hormone functioning.9

The results indicated that low and environmentally relevant concentrations of glyphosate possessed estrogenic activity. The study also found that there was an additive estrogenic effect between glyphosate and genistein, a phytoestrogen (plant estrogen) in soybeans. The authors concluded that their results needed further study in animals.24

The most toxic dose in this experiment, 10(-9) M, equals 169ng/L or 169 ppt (parts per trillion) glyphosate; 10(-12) M equals 0.169ng/L or 169 ppq (parts per quadrillion). Although 169 ppt glyphosate is above the EU maximum permitted level for drinking water – currently set at 100ng/L or 100ppt for any one pesticide active ingredient25 – clear estrogenic effects were also observed at progressively lower concentrations down to 10(-12)M,24 a concentration which falls within permitted levels in the EU.

In other words, glyphosate caused estrogenic effects and induced cancer cells to proliferate in vitro at a level permitted in drinking water in the EU.

How do these levels compare with the levels of glyphosate residues found in GM soy in a recent analysis? The researchers analyzed the composition of GM glyphosate-tolerant soybeans, industrially grown non-GM soybeans, and organic soybeans. They found that the GM soybeans contained high residues of glyphosate and its toxic metabolite AMPA (mean of 3.3 and 5.7 mg/kg, respectively), but industrially grown non-GM soybeans and organic soybeans contained neither chemical.2

Monsanto itself had previously called these levels of glyphosate “extreme”. It is clear that since the widespread cultivation of GM glyphosate-tolerant soybeans, “extreme” levels of glyphosate have become the new norm.18

Taking the figure of 3.3 mg/kg of glyphosate in the GM soybeans (excluding the AMPA), this is equivalent to 3.3 ppm or 3,300 ppb. This is a staggering 19,500-fold higher concentration than the 10(-9)M level found toxic in the in vitro experiment and 19,500,000-fold higher than the 10(-12) M level, also found to have estrogen-mimicking effects.24 In short, the level of glyphosate in the soy was well above that found to have estrogenic effects on the breast cancer cells in vitro.

Qualifications and questions

When evaluating the importance of these findings, a number of qualifications and unresolved questions need to be considered.

Most importantly, we do not know how much of the glyphosate in the soy is absorbed by the human or animal consumer when present at these levels in food or feed. Since so little is required to have an estrogenic effect in vitro, it is possible that enough can be taken up and accumulate in the body to have hormone-disrupting effects, including stimulation of estrogen-dependent breast cancer growth. But we do not know that for certain because there are major gaps in our knowledge regarding the absorption, accumulation and excretion rates of glyphosate and AMPA.

The amounts of glyphosate found in the urine of EU citizens in a survey conducted by Friends of the Earth26 may be biologically significant and have a hormone-disruptive effect, especially as exposure takes place over long periods. Again, no one knows for certain.

Although the mean levels found in the soy of 3.3 mg/kg for glyphosate and 5.7 mg/kg for AMPA2 are below the maximum residue limit set for soy in Europe (20 mg/kg glyphosate), that does not mean that these levels are safe to consume. Also, the official limit does not take into account the increased toxicity of the complete commercial formulations, including adjuvants, over the isolated active ingredient. As stated above, the formulations have not been tested for long-term toxicity.

We conclude from these results, taken together, that people who eat food products from GM Roundup Ready crops are eating amounts of these substances that may have toxic – particularly endocrine disruptive – effects. Further animal testing would be necessary to confirm or refute this possibility.

In vitro versus in vivo studies

Findings of toxicity from in vitro experiments involving cells grown in tissue culture need to be confirmed in animal studies (in vivo). This is because in the current state of scientific knowledge we cannot fully understand from in vitro studies how the same toxin would affect a living mammal. Nevertheless, findings of toxicity in studies carried out in vitro should not be ignored (as regulators and industry all too often do), but should be treated as indicators of the need for further studies in animals. Such animal studies should test environmentally relevant low doses of the complete pesticide formulation over long periods of time, mirroring human exposures.

People and animals are widely exposed to glyphosate

Glyphosate-based herbicides are not only used by farmers. They are also widely used in non-farm environments to control weeds – for example, on roadsides and railway lines and in parks and school grounds, as well as by home gardeners. So even city-dwellers’ exposure to glyphosate can be significant. In agricultural areas where GM glyphosate-resistant crops are grown, exposure is likely to increase exponentially.

Unsurprisingly, glyphosate and its metabolite AMPA are widely found in the environment and in the bodies of people and animals. Study findings include:

  • Glyphosate and its toxic metabolite AMPA were found in over 75% of the air and rain samples tested from the Mississippi Delta agricultural region in 2007. The researchers noted that the widespread presence of glyphosate was due to the cultivation of GM glyphosate-tolerant crops.27
  • Glyphosate and AMPA were frequently detected in streams in the American Midwest during the growing season.28
  • In a monitoring programme in Denmark, glyphosate and AMPA were washed out of the root zone of some types of soil and into drainage water in average concentrations that exceeded the EU permitted limit for drinking water (0.1 μg/l).29,30
  • Glyphosate was found circulating in the blood of non-pregnant women living in Canada. The amounts of glyphosate detected ranged from undetectable to 93.6 ng/ml (93.6μg/L), with an average of 73.6ng/ml (73.6μg/L).31 Worryingly, this is well within the range of glyphosate concentration found in vitro to have endocrine disruptive effects on the estrogen hormone system,24 which can lead to slow-onset disease upon long-term exposure and adverse reproductive and developmental effects in offspring.9
  • In an in vitro study modelling human exposures, 15% of administered glyphosate crossed the human placental barrier and entered the foetal compartment.32 The study showed that the placental barrier in mammals does not protect the unborn foetus from glyphosate exposures.
  • Laboratory testing commissioned by two civil society organizations found levels of glyphosate in American women’s breast milk of 76 μg/L to 166 μg/L – that is, 760 to 1600 times higher than the EU permitted level in drinking water. These levels were, however, less than the 700 μg/Lmaximum contaminant level (MCL) for glyphosate in drinking water in the US. Tests on the women’s urine found maximum glyphosate levels over 8 times higher than those found in the urine of Europeans33 (see next item below). These high levels raise the question of whether glyphosate bioaccumulates in our bodies. If it does, then so-called safe levels are meaningless, since the glyphosate could build up to dangerous levels even if daily exposures are low.
  • In laboratory testing commissioned by Friends of the Earth, glyphosate and AMPA were found in the urine of respectively 44% and 36% of European city dwellers. Levels detected varied but the highest levels of glyphosate and AMPA were respectively 1.8 μg/L and 2.6 μg/L.34
  • Urinary levels of glyphosate were 1.6 ppb in farming fathers and 1.5 ppb in non-farming fathers. For farming mothers, levels were 1.1 ppb, and for non-farming mothers, 1.2 ppb. For children of farmers, the levels were 1.9 ppb, and for children of non-farming families, the glyphosate urinary levels were 2.5 ppb. Urinary burdens in non-farm children were slightly higher than those in farm children. The authors suggested that this was because of the widespread use of glyphosate in non-farm areas, such as in home gardens.35
  • Glyphosate was found in the urine of cows, humans, and rabbits. Cows kept in a GM-free area had significantly lower glyphosate concentrations in urine than cows in conventional livestock systems. Glyphosate was also detected in the intestines, liver, muscles, spleen and kidney of slaughtered cows. Glyphosate levels were significantly higher in urine of humans who ate non-organic food, compared with those who ate mostly organic food. Chronically ill people showed significantly higher glyphosate residues in their urine than healthy people.36

Are these levels dangerous? No one knows, as the necessary testing of presumed safe “acceptable daily intake” levels has not been done in animals; and neither have the complete herbicide formulations as sold and used been tested at realistic exposure levels.

There is cause for concern and sound justification for applying the precautionary principle at the individual and societal levels to minimize exposure until direct experimentation testing the acceptable daily intake has been evaluated in long-term feeding studies.

People and animals are not protected by current regulations

An analysis of glyphosate’s current approval in the EU and in the US suggests that the “acceptable daily intake” (ADI) level, the level of exposure that is deemed safe for humans over a long period of time, is inaccurate and dangerously high.11

Regulators calculate the ADI on the basis of industry studies submitted to the regulators in support of the application for the chemical’s approval. The figure used to set the ADI is the highest dose at which no adverse effect is found (the No Observed Adverse Effect Level or NOAEL), which is also lower than the lowest dose that has a toxic effect (the Lowest Observed Adverse Effect Level or LOAEL). The ADI is derived by dividing this figure by 100, to allow a safety margin.11

The current EU8 and Australasian37 ADI for glyphosate is 0.3 mg/kg bw/d.

But this ADI has been shown to be inaccurate and potentially dangerously high by two independent rat feeding studies on Roundup. The studies found that:

  • Roundup was a potent endocrine disruptor and caused disturbances in the reproductive development of rats when the exposure was performed during the puberty period. Adverse effects, including delayed puberty and reduced testosterone production, were found at all dose levels, including the LOAEL of 5 mg/kg bw/d.12
  • Glyphosate herbicide caused damage to rats’ liver cells that the researchers said was probably “irreversible” at a dose of just 4.87 mg/kg bw/d.13

These studies did not find a safe or “no effect” level (NOAEL). Even the lowest dose tested produced a toxic effect and no further experiments were done with lower doses to establish the NOAEL. A reasonable estimate of the NOAEL based on these studies might be 2.5 mg/kg of body weight – though this level would have to be tested in long-term studies, using the complete formulation, to gain more certainty. Then, applying the 100-fold safety factor, the ADI should be 0.025 mg/kg bw/d – 12 times lower than the level for glyphosate currently in force in the EU.11

Even if only the industry studies are considered, the current ADI should still be lower. An objective analysis of these studies results in a more objectively accurate ADI of 0.1 mg/kg bw/d, one-third of the current ADI.11

It should be borne in mind, however, that since glyphosate herbicides are known to have endocrine disrupting properties, they may be toxic at far lower doses than this. This possibility has not been explored in regulatory tests. If the very low levels found to be disrupt hormones in an independent study in vitro24 were found to do the same in vivo, then no safe dose could be claimed and glyphosate herbicides would have to be banned. The extremely low dose toxicity of Roundup found in Professor Gilles-Eric Séralini’s two-year rat feeding study38 is a testament to this possibility.

Wildlife not protected by recommended application rates

There is evidence that Roundup spray rates recommended by manufacturers do not protect amphibians. A study in a natural setting found that Roundup application at the rate recommended by the manufacturer eliminated two species of tadpoles and nearly exterminated a third species, resulting in a 70% decline in the species richness of tadpoles. Contrary to common belief, the presence of soil does not reduce the chemical’s effects.39 Further experiments with lower concentrations, well within levels to be expected in the environment, still caused 40% amphibian mortality.40


GM Roundup Ready (RR) soy is the most widely grown GM crop. It is engineered to tolerate being sprayed with Roundup herbicide, based on the chemical glyphosate. The majority of GM RR soy goes into animal feed for intensive livestock feedlots in Europe and other industrialized countries. Widespread planting of GM RR soy in North and South America has led to large increases in the amount of glyphosate herbicide used. Regulators have responded by raising the allowed maximum residue limit of glyphosate in crops eaten by people and animals. GM RR soy has been found to contain high levels of glyphosate residues, above those found to cause cancer cells to multiply in vitro. People and animals that eat GM RR crops are eating potentially toxic and endocrine disruptive amounts of herbicide residues.

Claims by regulators and industry that these levels of Roundup are safe are based on industry studies on glyphosate alone. Regulators’ interpretation of these industry studies is open to question, as some of the studies showed toxic effects below the level claimed by regulators to show no effect. Effects found in animal studies and studies on human cells grown under laboratory conditions include cell death and damage, damage to DNA, disruption of hormones, birth defects, and cancer. Some of these effects have been found at levels far below those used in agriculture and corresponding to low levels of residues in food and feed. The added ingredients in Roundup (adjuvants) increase the toxicity of glyphosate, and the main metabolite of glyphosate, AMPA, is also toxic.

The risk of increased exposure to Roundup residues due to the presence of GM RR crops in our food and feed supply has not been adequately considered in regulatory assessments.


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