Glyphosate, a component of Monsanto’s herbicide Roundup, is expected to be added to the list of cancer-causing chemicals as per California’s Safe Drinking Water and Toxic Enforcement Act of 1986, a.k.a. Proposition 65, by the State’s Environmental Protection Agency early July. This action does not make it illegal to sell Roundup or other herbicides that contain glyphosate in the state. However, herbicide manufacturers will be required to put a warning label on glyphosate-based products before next year.
Glyphosate is a non-selective herbicide. Its plant-killing mechanism involves blocking the shikimic acid or shikimate pathway, which is essential for the biosynthesis of folates and aromatic amino acids in plants and some microorganisms. Pure glyphosate is low in acute toxicity, but other ingredients in the formulation of herbicides can improve bioavailability to human thus enhance the toxicity of the glyphosate. Eye or skin irritation are among common symptoms to people who are exposed to glyphosate, and those who inhaled the herbicide mist were reported to feel irritation in their nose and throat.
Chemical structure of glyphosate. Credit: wikipedia
Many regulatory bodies have evaluated the link between glyphosate and development cancer in human. The International Agency for Research on Cancer (IARC), the cancer-research arm of the World Health Organization (WHO) has listed glyphosate in the class of chemicals that are “probably carcinogenic to humans”, or also known as Category 2A based the agency’s own evaluation. Items in this category includes commonly used pure and mixed chemicals such as acrylamide and bitumens, and chemotherapeutics such as doxorubin and cisplatin.
Although several studies that focused on people who work with the herbicide have found increased risk of non-Hodgkin lymphoma, data from a large US study which followed thousands of farmers contradicted this conclusion. Evidence that led the IARC to its ‘probably carcinogenic’ classification mostly came from observation of carcinogenesis in animals and in vitro study on human cells, and limited human data.
Agricultural use of glyphosate in US. Credit: wikipedia
Monsanto, the creator of Roundup, had unsuccessfully sued the California government to prevent the move last year when the state initialized the process to add glyphosate to Proposition 65. Despite the first failed attempt, the herbicide and agrichemical giant has pledged to appeal. Upon winning the appeal, their products would not make the list of dangerous chemicals.
An industry group of called the Glyphosate Task Force (Monsanto as a member) has previously denounced the classification of glyphosate by IARC, stating that the WHO division had “purposefully disregarded dozens of scientific studies” that showed no genetic toxicity. What is interesting, some academic scientists also cautioned that the “probable carcinogenic” classification of glyphosate by IARC lacks sufficient evidence.