Dan Wilson
Senior Member.
Recently, the International Society of Doctors for the Environment (ISDE) called for a ban on glyphosate (the active ingredient in Roundup) use as an herbicide in agriculture, citing the International Agency for Research on Cancer's (IARC) new classification of the chemical as 2A (probably carcinogenic) as their reason. This has been spreading through social media and various news sites and people are getting behind the idea of banning glyphosate, one of the most widely used herbicides on the planet. So, is it really toxic? And should consumers worry about it?
How it works:
Let's start by talking about how glyphosate works. Glyphosate is an herbicide that targets a particular biochemical pathway in plants in order to kill them. This pathway is called the Shikimate pathway, and the purpose of it is to synthesize amino acids containing aromatic rings (tryptophan, tyrosine, and phenylalanine) which are built into proteins necessary for life. Glyphosate inhibits this pathway by mimicking a metabolite called phoshoenolpyruvate (PEP) and stopping a key enzyme in the pathway. Since plants must produce all of their energy and all of their biological molecules themselves, inhibiting this pathway means the plant can't produce particular amino acids, which means it can't produce proteins correctly, and so it dies.
Humans and other animals do not possess this pathway, the genes and corresponding proteins simply aren't there. Instead, these three aromatic amino acids are obtained through our diet. This is why two out of these three amino acids are considered essential (tyrosine is conditionally essential) and also why glyphosate cannot outright kill animals.
Toxicity:
Although it cannot kill animals the way it can plants and certain bacteria, glyphosate can be toxic. But anything can be toxic in the right context since the dosage makes the poison. Biochemically, it can be suspected to be toxic since it mimics PEP and multiple enzymes (not just the Shikimate pathway) use PEP as its substrate. But let's look at the evidence. Glyphosate has been extensively researched by multiple labs all around the world. The oral rat LD50 for glyphosate is 4,320 mg/kg. By comparison, caffeine (192 mg/kg), nicotine (0.5-1 mg/kg), and table salt (3,000 mg/kg) are more toxic than glyphosate.
Chronic toxicity to humans has also been assessed in populations of workers who spray the herbicide on a regular basis and no significant differences were detected.
http://npic.orst.edu/factsheets/glyphotech.html
https://www.ncbi.nlm.nih.gov/pubmed/2011980 (more direct link)
Carcinogenicity:
Carcinogenicity (potential to cause cancer) and toxicity aren't all that different, but here we will talk about them separately. The carcinogenicity of glyphosate has been assessed as well and conflicting evidence has been collected, but the overall body of research supports the idea that glyphosate is not carcinogenic.
http://informahealthcare.com/doi/pdf/10.3109/10408444.2013.770820
Should consumers worry about it?:
Think now about how much glyphosate actually makes it from crops in the field to the food on your plate. When glyphosate is sprayed onto crops, it acts on the plants it is meant to kill but does not linger in the environment. Glyphosate in soil is quickly broken down into aminomethylphosphonic acid (AMPA) (which further breaks down to naturally occurring soil components) and carbon dioxide. AMPA has also been determined to not be harmful to humans. After harvesting and washing the crops, it is likely that hardly any glyphosate at all is consumed. Look now at all of the doses given to rats in the various studies that have been referenced here. Humans aren't likely to ever consume glyphosate in amounts needed to see negative effects. The lowest observed adverse effect level (LOAEL) for glyphosate, determined in carcinogenicity studies, is 4,500 mg/kg/day. For a human weighing 150lb., that's 306 grams per day.
In summary, glyphosate works biochemically in a way that does not affect animals the same way it affects plants. All substances can be toxic but the dose makes the poison. Glyphosate toxicity in animal models and humans has been assessed and studied in labs all over the world and has been determined to not pose a significant risk to health at doses and concentrations that are relevant, especially to everyday people. The IARC's position on glyphosate stated as "probably carcinogenic" is not concrete, although other organizations like the EPA are currently doing more reviews on glyphosate toxicity and are giving the recommendation further consideration. The claims of negative health effects that are being used to push for a ban on the use of glyphosate are unsupported by the extensive body of research currently available.
As a last note, the Seralini paper which claims to demonstrate glyphosate and GM maize's carcinogenicity in rats is purposely not discussed here, as it has been retracted and already thoroughly criticized both on this web site and other places.
EDIT:
Myles Power recently posted a video reviewing the IARC's monograph and I highly recommend it. I think they do a better job of criticizing the classification than I do here.
How it works:
Let's start by talking about how glyphosate works. Glyphosate is an herbicide that targets a particular biochemical pathway in plants in order to kill them. This pathway is called the Shikimate pathway, and the purpose of it is to synthesize amino acids containing aromatic rings (tryptophan, tyrosine, and phenylalanine) which are built into proteins necessary for life. Glyphosate inhibits this pathway by mimicking a metabolite called phoshoenolpyruvate (PEP) and stopping a key enzyme in the pathway. Since plants must produce all of their energy and all of their biological molecules themselves, inhibiting this pathway means the plant can't produce particular amino acids, which means it can't produce proteins correctly, and so it dies.
Humans and other animals do not possess this pathway, the genes and corresponding proteins simply aren't there. Instead, these three aromatic amino acids are obtained through our diet. This is why two out of these three amino acids are considered essential (tyrosine is conditionally essential) and also why glyphosate cannot outright kill animals.
Toxicity:
Although it cannot kill animals the way it can plants and certain bacteria, glyphosate can be toxic. But anything can be toxic in the right context since the dosage makes the poison. Biochemically, it can be suspected to be toxic since it mimics PEP and multiple enzymes (not just the Shikimate pathway) use PEP as its substrate. But let's look at the evidence. Glyphosate has been extensively researched by multiple labs all around the world. The oral rat LD50 for glyphosate is 4,320 mg/kg. By comparison, caffeine (192 mg/kg), nicotine (0.5-1 mg/kg), and table salt (3,000 mg/kg) are more toxic than glyphosate.
Chronic toxicity to humans has also been assessed in populations of workers who spray the herbicide on a regular basis and no significant differences were detected.
https://www.ncbi.nlm.nih.gov/pubmed/2011980 (more direct link)
Glyphosate has been shown not to have any obvious immediate or long-term toxicity in those who would be exposed to it much more than a normal consumer might. The news story being sent around, however, is specifically about cancer and glyphosate.Five forestry workers sprayed glyphosate for 6 hours a day over the course of a week. No statistically significant differences were found in medical examinations and laboratory testing performed on the workers following pesticide application.30
Carcinogenicity:
Carcinogenicity (potential to cause cancer) and toxicity aren't all that different, but here we will talk about them separately. The carcinogenicity of glyphosate has been assessed as well and conflicting evidence has been collected, but the overall body of research supports the idea that glyphosate is not carcinogenic.
http://informahealthcare.com/doi/pdf/10.3109/10408444.2013.770820
http://npic.orst.edu/factsheets/glyphotech.htmlThis evaluation of the large volume of genotoxicity data available presents a convincing weight of evidence supporting the lack of genotoxic potential for both glyphosate and typical GBFs in core gene mutation and chromosomal effect endpoints.
Researchers fed rats a diet containing glyphosate at 0, 89, 362, or 940 mg/kg/day (males) and 0, 113, 457, or 1183 mg/kg/day (females) for two years. The low-dose and high-dose male groups had a slightly increased incidence of pancreatic islet cell adenomas and hepatocellular adenomas. The mid-dose and high-dose male and female groups had a slightly increased incidence of thyroid C-cell adenomas. The U.S. EPA concluded the adenomas were not treatment related.27
In addition to the EPA's classification of glyphosate, the European Food Safety Authority also does not recommend a classification of carcinogenicity, finding insufficient evidence to support such an idea. So, take it as you will, but the IARC is, in fact, alone in its position on glyphosate. At least as far as official assessments go.The U.S. EPA classified glyphosate as Group E, evidence of non-carcinogenicity in humans. The U.S. EPA does not consider glyphosate to be a human carcinogen based on studies of laboratory animals that did not produce compelling evidence of carcinogenicity.6 See the text box on Cancer.
Should consumers worry about it?:
Think now about how much glyphosate actually makes it from crops in the field to the food on your plate. When glyphosate is sprayed onto crops, it acts on the plants it is meant to kill but does not linger in the environment. Glyphosate in soil is quickly broken down into aminomethylphosphonic acid (AMPA) (which further breaks down to naturally occurring soil components) and carbon dioxide. AMPA has also been determined to not be harmful to humans. After harvesting and washing the crops, it is likely that hardly any glyphosate at all is consumed. Look now at all of the doses given to rats in the various studies that have been referenced here. Humans aren't likely to ever consume glyphosate in amounts needed to see negative effects. The lowest observed adverse effect level (LOAEL) for glyphosate, determined in carcinogenicity studies, is 4,500 mg/kg/day. For a human weighing 150lb., that's 306 grams per day.
In summary, glyphosate works biochemically in a way that does not affect animals the same way it affects plants. All substances can be toxic but the dose makes the poison. Glyphosate toxicity in animal models and humans has been assessed and studied in labs all over the world and has been determined to not pose a significant risk to health at doses and concentrations that are relevant, especially to everyday people. The IARC's position on glyphosate stated as "probably carcinogenic" is not concrete, although other organizations like the EPA are currently doing more reviews on glyphosate toxicity and are giving the recommendation further consideration. The claims of negative health effects that are being used to push for a ban on the use of glyphosate are unsupported by the extensive body of research currently available.
As a last note, the Seralini paper which claims to demonstrate glyphosate and GM maize's carcinogenicity in rats is purposely not discussed here, as it has been retracted and already thoroughly criticized both on this web site and other places.
EDIT:
Myles Power recently posted a video reviewing the IARC's monograph and I highly recommend it. I think they do a better job of criticizing the classification than I do here.
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