How safe are “safe” levels of glyphosate?

Summary

Industry and regulators claim that we are only exposed to “safe” levels of glyphosate and Roundup that do not cause toxic effects. Safety levels have been determined by toxicity tests on laboratory animals. A growing body of evidence indicates that these tests are inadequate to determine toxic effects of glyphosate and Roundup residues and that consumption of these residues may be a risk to health.

Frequently, industry and regulators claim that toxic effects caused by glyphosate and Roundup in animal studies do not matter because we are only exposed to “safe” levels that do not cause such effects.

Regulators set safety limits for exposure to glyphosate based on data from industry’s own toxicity studies on laboratory animals. These toxicity studies are supposed to provide evidence of potential adverse effects on mammals, most commonly rats, whose physiology is similar to that of humans. The long-term experiments are based on analyses of blood and organs and last two years, around two-thirds of the average lifespan of a rat. Companies conduct different tests according to standards set in consultation with industry by the Organization for Economic Co-operation and Development (OECD), a body dedicated not to public health but to facilitating international trade.

The results of these industry tests, which are classified as commercial secrets and kept hidden from the public and the scientific community, are presented to expert panels in government or food safety agencies based in various countries or regions, such as the European Union.

To assess whether or not an exposure is a health risk, a safety threshold called the acceptable daily intake (ADI) is calculated. The ADI is an estimate of the amount of a substance in food or drinking water, expressed on a body mass basis, which can be ingested daily over a lifetime by humans without appreciable health risks.

In the case of glyphosate, the ADI value differs from country to country. It has been set at 0.3 mg per kg of bodyweight per day (written as 0.3 mg/kg bw/d) in Europe, and 1.75mg/kg bw/d in the USA. The calculation to set the ADI is based on the lowest dose considered non-toxic in animal feeding trials (30mg/kg bw/d) sponsored by industry.

Are these levels safe? There are several reasons to doubt the validity of the current ADI values for glyphosate, including:

  • The so-called safe levels of glyphosate exposure have never been tested directly to determine if indeed they are really safe to consume over the long term. Instead the “safe” levels are extrapolated from higher doses tested in industry studies.
  • Industry toxicity study protocols are out of date. All toxicity tests conducted by industry for regulatory purposes are based on the old adage, “The dose makes the poison,” – that is, the higher the dose, the greater the degree of toxicity. However, in some cases, low doses corresponding to human exposures can be more toxic than the higher doses tested in laboratory animals in industry studies. This is especially true for chemicals that disrupt the hormonal system (endocrine disruptors).1 Safe levels of these chemicals cannot be extrapolated from effects at higher doses. Evidence from in vitro2 and animal3 experiments shows that glyphosate may be an endocrine disruptor at levels permitted in tap water in the EU.
  • NEW 2017 STUDY: A new study published in Scientific Reports14, an online, open access journal from the publishers of Nature, has shown that the glyphosate-based Roundup herbicide causes non-alcoholic fatty liver disease in rats at very low doses.
  • Findings that glyphosate and its commercial formulations may be endocrine disruptors2 3 imply that the standard industry long-term animal studies are inadequate. These studies are conducted on adult animals, and fail to test the effects of exposure during important windows of development, such as foetal development. Yet hormones are vital regulators of development. A subtle hormonal effect during early life can modify organ morphology and function for the rest of the life, as well as potentially leading to chronic diseases such as cancer and reproductive dysfunction in adults.1
  • The complete glyphosate herbicide formulations as sold and used contain additives (adjuvants), which are toxic in their own right and/or increase the toxicity of glyphosate.4 Safety limits are set for the isolated ingredient glyphosate, but the whole formulations, which are generally more toxic, are never tested to determine long-term toxic effects. This limitation of the regulatory process applies to all pesticides in all countries worldwide. Studies in rats confirm that the complete glyphosate herbicide formulations are toxic at levels deemed safe by regulators for the isolated ingredient glyphosate.5 6 7 Other feeding studies in pigs8 and rats9 directly comparing the toxicity of formulations with glyphosate alone found that the formulations were far more toxic.
  • Even glyphosate alone may not be as safe as claimed. Industry tests on glyphosate alone revealed toxic effects, notably birth defects,5 below the levels that regulators claimed showed no toxic effect – but these results were ignored or dismissed by regulators in setting the supposedly safe ADI
  • Independent studies have found toxic effects of glyphosate and its commercial formulations at environmentally realistic levels, which have never been tested by regulators. Effects include oxidative stress on liver and kidneys10 3 and endocrine disrupting effects.2

Glyphosate, which was claimed to be as safe as table salt11 12 for over 40 years, was reclassified as a probable carcinogen by the World Health Organization in 2015.13 Glyphosate has never been tested during sensitive periods of life (such as foetal development) at environmental levels of exposure. In addition, the fact that its commercial formulations have never been tested for more than one month in rats, and that without any blood testing, raises further doubt as to the validity of current ADI values.

These findings, taken as a whole, suggest that the levels of Roundup we are exposed to may not be safe over the long term.

 

References:
  1. Vandenberg LN, Colborn T, Hayes TB, et al. Hormones and endocrine-disrupting chemicals: Low-dose effects and nonmonotonic dose responses. Endocr Rev. 2012;33(3):378-455. doi:10.1210/er.2011-1050.
  2. Thongprakaisang S, Thiantanawat A, Rangkadilok N, Suriyo T, Satayavivad J. Glyphosate induces human breast cancer cells growth via estrogen receptors. Food Chem Toxicol. 2013;59:129-136. doi:10.1016/j.fct.2013.05.057.
  3. Séralini G-E, Clair E, Mesnage R, et al. Republished study: long-term toxicity of a Roundup herbicide and a Roundup-tolerant genetically modified maize. Environ Sci Eur. 2014;26(14). doi:10.1186/s12302-014-0014-5.
  4. Mesnage R, Bernay B, Seralini GE. Ethoxylated adjuvants of glyphosate-based herbicides are active principles of human cell toxicity. Toxicology. 2013;313(2013):122-128. doi:10.1016/j.tox.2012.09.006.
  5. Antoniou M, Habib MEM, Howard CV, et al. Teratogenic effects of glyphosate-based herbicides: Divergence of regulatory decisions from scientific evidence. J Env Anal Toxicol. 2012;S4:006. doi:10.4172/2161-0525.S4-006.
  6. Romano RM, Romano MA, Bernardi MM, Furtado PV, Oliveira CA. Prepubertal exposure to commercial formulation of the herbicide Glyphosate alters testosterone levels and testicular morphology. Arch Toxicol. 2010;84:309-317.
  7. Benedetti AL, Vituri C de L, Trentin AG, Domingues MA, Alvarez-Silva M. The effects of sub-chronic exposure of Wistar rats to the herbicide Glyphosate-Biocarb. Toxicol Lett. 2004;153:227-232. doi:10.1016/j.toxlet.2004.04.008.
  8. Lee H-L, Kan C-D, Tsai C-L, Liou M-J, Guo H-R. Comparative effects of the formulation of glyphosate-surfactant herbicides on hemodynamics in swine. Clin Toxicol Phila Pa. 2009;47(7):651-658. doi:10.1080/15563650903158862.
  9. Adam A, Marzuki A, Abdul Rahman H, Abdul Aziz M. The oral and intratracheal toxicities of ROUNDUP and its components to rats. Vet Hum Toxicol. 1997;39(3):147-151.
  10. Larsen K, Najle R, Lifschitz A, Virkel G. Effects of sub-lethal exposure of rats to the herbicide glyphosate in drinking water: glutathione transferase enzyme activities, levels of reduced glutathione and lipid peroxidation in liver, kidneys and small intestine. Environ Toxicol Pharmacol. 2012;34(3):811-818. doi:10.1016/j.etap.2012.09.005.
  11. Charry T. Monsanto recruits the horticulturist of the San Diego Zoo to pitch its popular herbicide. The New York Times. http://www.nytimes.com/1997/05/29/business/monsanto-recruits-horticulturist-san-diego-zoo-pitch-its-popular-herbicide.html. Published May 29, 1997. Accessed April 3, 2015.
  12. Preston C. Comment on “Is glyphosate toxic to humans?” by Anastasia Bodnar. Biol Fortif. 2014. http://www.biofortified.org/2013/10/glyphosate-toxic/.
  13. Guyton K, Loomis D, Grosse Y, El Ghissassi F, Benbrahim-Tallaa L. Carcinogenicity of tetrachlorvinphos, parathion, malathion, diazinon, and glyphosate. Lancet Oncol. 2015. http://www.thelancet.com/pdfs/journals/lanonc/PIIS1470-2045%2815%2970134-8.pdf.
  14. Multiomics reveal non-alcoholic fatty liver disease in rats following chronic exposure to an ultra-low dose of Roundup herbicide http://www.nature.com/articles/srep39328

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