Some studies suggest that both glyphosate and Roundup are possibly neurotoxins (toxic to the nervous system). Neurological diseases in humans include Parkinson’s disease, Alzheimer’s disease, and some forms of depression. Neurodevelopmental toxicity to the growing foetus or to babies can result in autism and attention deficit hyperactivity disorder (ADHD).
The pesticide industry website Glyphosate Facts (glyphosate.eu), claims, “Multiple long-term animal studies with glyphosate have failed to demonstrate any evidence of neurotoxicity.”1 As is consistently the case on this website, however, the cited studies are industry studies, which the public and independent scientists are not allowed to see, and which were conducted on glyphosate alone. They are not adequate to assess the toxicity of the complete herbicide formulations that the public is exposed to.
Industry has not conducted any long-term neurotoxicity studies on Roundup, the substance that people and animals are actually exposed to.
Some independent studies suggest that both glyphosate and Roundup are neurotoxins.
A toxicological study on rats found that glyphosate depleted the neurotransmitters serotonin and dopamine,2 though it is not clear whether the test substance was pure glyphosate or a complete commercial formulation. Neurotransmitters are chemicals in our bodies that transmit signals from one brain cell to another.
An epidemiological study carried out in Minnesota, USA found that the children of pesticide applicators exposed to glyphosate herbicides had an increased incidence of neurobehavioral disorders, including ADHD (attention deficit hyperactivity disorder). The finding suggested that glyphosate herbicide impacts neurological development.4
In a study by Argentine researchers, glyphosate was found to injure rat brain and liver cells. Glyphosate was more toxic in combination with the fungicide zineb and the systemic insecticide dimethoate than on its own. These three chemicals are often used in combination in Argentina. The researchers commented that their results were consistent with the possibility that these chemicals play a role in the development of the neurological disorder Parkinson’s disease.3
A clinical case study described how a man5 who was exposed to glyphosate herbicide developed the neurological disorder Parkinson’s disease. A separate case study involving a woman6 found the same result, though in this case it is not clear if the exposure was to glyphosate alone or a complete formulation, as the exposure took place in a factory that manufactured herbicides.6
Glyphosate Facts says of these case studies, “the existence of significant systemic exposure to glyphosate in these cases is questionable, given the poor absorption of glyphosate through the human skin and its low volatility”.1 But there is no experimental data showing how much glyphosate (and Roundup adjuvants and metabolites) ends up in the human body after exposure. Nor is it known by which routes it gets there – for example, how much comes from food and drink consumed, or from inhalation or skin contact. So Glyphosate Facts is questioning these studies on the basis of inadequate evidence.
An in vitro study suggested a mechanism through which glyphosate could cause Parkinson’s disease: glyphosate alone was found to induce programmed cell death and degradation leading to death in PC12 cells – human cells that serve as an experimental model for nerve cells.7
- Glyphosate Task Force. Can glyphosate exposure be linked to Parkinson’s disease? Glyphosate Facts. 2013. Available at: http://www.glyphosate.eu/can-glyphosate-exposure-be-linked-parkinsons-disease.
- Anadón A, del Pino J, Martínez MA, et al. Neurotoxicological effects of the herbicide glyphosate. Toxicol Lett. 2008;180S:S164.
- Astiz M, de Alaniz MJ, Marra CA. Effect of pesticides on cell survival in liver and brain rat tissues. Ecotoxicol Env Saf. 2009;72:2025-32. doi:10.1016/j.ecoenv.2009.05.001.
- Garry VF, Harkins ME, Erickson LL, Long-Simpson LK, Holland SE, Burroughs BL. Birth defects, season of conception, and sex of children born to pesticide applicators living in the Red River Valley of Minnesota, USA. Env Health Perspect. 2002;110 Suppl 3:441-9.
- Barbosa ER, Leiros da Costa MD, Bacheschi LA, Scaff M, Leite CC. Parkinsonism after glycine-derivate exposure. Mov Disord. 2001;16:565–568.
- Wang G, Fan XN, Tan YY, Cheng Q, Chen SD. Parkinsonism after chronic occupational exposure to glyphosate. Park Relat Disord. 2011;17:486-7. doi:10.1016/j.parkreldis.2011.02.003.
- Gui YX, Fan XN, Wang HM, Wang G, Chen SD. Glyphosate induced cell death through apoptotic and autophagic mechanisms. Neurotoxicol Teratol. 2012;34(3):344–349.