Does Roundup harm mammals?

Question

In the anti-GMO debate, it is frequently suggested that the use of Glyphosate (trade name: Roundup) on Roundup-ready GMO crops causes environmental harm.

• Example claim: Natural News

Monsanto's infamous Roundup contains the hotly debated compound called glyphosate. This merciless herbicide is also found in 750 or more U.S. products. An herbicide like this infiltrates the landscape and accumulates in mammals, especially bone, hindering cellular detoxification along the way.

A destroyer, glyphosate annihilates a plant's building blocks of life, tearing apart amino acids. By disrupting the "shikimate pathway" in plants and microorganisms, glyphosate creeps inside leaves and stalk, raping natural life processes. Glyphosate also destroys the beneficial microorganism in the human gut, destroying the human immune system.

Does the use of Roundup accumulate in mammals and cause illness?

Answer 1

According to this Cornell University toxicology report, no.

Chronic Toxicity

Subchronic and chronic tests with glyphosate have been conducted with rats, dogs, mice, and rabbits in studies lasting from 21 days to two years. With few exceptions there were no treatment-related gross (easily observable) or cellular changes (5). In a chronic feeding study with rats, no toxic effects were observed in rats given doses as high as 31 mg/kg/day, the highest dose tested. No toxic effects were observed in a chronic feeding study with dogs fed up to 500 mg/kg/day, the highest dose tested (8). Mice fed glyphosate for 90 days exhibited reduced body weight gains. The lifetime administration of very high amounts of glyphosate produced only a slight reduction of body weight and some microscopic liver and kidney changes. Blood chemistry, cellular components, and organ function were not affected even at the highest doses.

Hens fed massive amounts over three days and again 21 days later showed no nerve related effects.

Source: http://pmep.cce.cornell.edu/profiles/extoxnet/dienochlor-glyphosate/glyphosate-ext.html

Answer 2

Your question is a bit complex: "Does the use of Roundup accumulate in mammals and cause illness?"

I'm going to focus on a slightly simplified version of the question, for sanity sake:

Does glyphosate cause illness?

The answer to this much simpler question is clearly "Yes." But that alone does not mean that glyphosate is pure evil; many things can cause illness, depending on concentration and other circumstances. See my closing comments for more on this...

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The Pesticide Action Network of the UK has a well-referenced, and seemingly un-biased fact sheet on the topic of glyphosate. It discusses varoius types of toxicity, and on the topic of mamalian toxicity, it says in summary

There is nevertheless evidence of toxic effects on humans as well as environmental toxicity, indirect environmental damage and resistance in some target weed species.

Specifically:

Acute Toxicity

The acute toxicity of glyphosate itself is very low. According to the World Health Organisation, the oral LD50 in the rat of pure glyphosate is 4,230 mg/kg, or 5,600 mg/kg according to Monsanto(6). The low acute toxicity of glyphosate can be attributed to its biochemical mode of action on a metabolic pathway in plants (called the shikimic acid pathway) which does not exist in animals(7). However, glyphosate can also disrupt functions of enzymes in animals. In rats it was found to decrease the activity of some detoxification enzymes when injected into the abdomen(8). In general, controlled toxicity tests report adverse symptoms from exposure to glyphosate only at extremely high doses, ie several grammes per kg body weight.

While glyphosate itself may be relatively harmless, some of the products with which it is formulated have a rather less benign reputation.

Chronic Toxicity

Some literature suggests that glyphosate can cause some chronic health effects and birth defects in certain test animals when administered at high doses over prolonged periods(15). Chronic feeding studies have shown reduced weight gain, blood and pancreatic effects, but no evidence of carcinogenicity to humans. A US EPA report says: "Effects on pregnant mothers and foetuses included diarrhoea, decreased weight gain, nasal discharge and death of mothers and kidney and digestive disorders in rat pups"(16).

It is extremely unlikely that human users or members of the public would be exposed to doses as high as those used in the trials, but extrapolating toxicity data from rats, mice and rabbits on which trials are run, to humans can be inaccurate and misleading.

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Note that this answer does not address the entirety of the question; this only focuses on the direct toxic effect of glyphosate on mammals; the question also makes the claim that glyphosate can destroy gut flora; this claim is not addressed, and that glyphosate can accumulate in bones, thus "hindering cellular detoxification" (whatever that means).

I think those other questions could be answered (the one about gut flora in particular), but I believe this answer shows sufficiently that glyphosate does have an effect on mammalian health. If all you want is a "yes or no" answer, the answer is clearly "yes." If you want an answer about degrees to which glyphosate harms mammals, the answer is much more complicated, and then the question of gut flora, etc, may be more relevant.

Answer 3

According to an assessment by the International Agency for Research on Cancer, the herbicide glyphosate (ingredient in Roundup), is probably carcinogenic to humans:

Kathryn Guyton, a senior toxicologist in the monographs programme at the IARC and one of the authors of the study, says, “In the case of glyphosate, because the evidence in experimental animals was sufficient and the evidence in humans was limited, that would put the agent into group 2A.”

For reference, Wikipedia has a List of IARC Group 2A carcinogenics. It is weaker than Group 1 (Carcinogenic to humans), but stronger than Group 2B (Possibly carcinogenic to humans).

However, according to Monsanto and other agrochemical companies, the methodology of the IARC study is poor and the conclusions invalid.

The article classifying glyphosate as probably carcinogenic to humans:

Guyton, K. Z. et al. Lancet Oncol. http://dx.doi.org/10.1016/S1470-2045(15)70134-8 (2015).

A Nature article reporting on the news, as well as reporting on criticism from Monsanto and others:

Widely used herbicide linked to cancer, Nature, March 2015, doi:10.1038/nature.2015.17181