Pesticides and Precaution: A Look into Health Canada’s Proposed Increase of Glyphosate Residue Limits

By Nadine L. Wellington and Emma C. Anderson, Science and Policy Exchange

When buying food at the grocery store, consumers often get more than they bargained for: invisible to the naked eye, many food products contain residues of agricultural pesticides.

While these products are pillars of industrial agri-business, their usage is being reevaluated worldwide. Recently, after receiving requests from the pesticide industry, Health Canada proposed to increase Maximum Residue Limits (MRLs) of the controversial herbicide glyphosate (Table 1). While it has been marketed as safe, biodegradable and non-leaching, there are several risks, leading some jurisdictions to reduce or phase out its use. The proposal has seen considerable opposition, including from the National Farmers Union, Canadian Organic Trade Association and Bloc Quebecois, prompting a pause on the decision until 2022. In this article, we dive into glyphosate’s benefits, risks, and controversies to weigh in on the proposal.

Table 1: Current and Proposed Canadian Maximum Residue Limits for Glyphosate on Foods (ppm)

Glyphosate is the active ingredient in glyphosate-based herbicides (GBHs), the most-used herbicides in the world. GBHs often contain glyphosate mixed with salts and additives, like surfactants, to improve effectiveness. When applied, it blocks an enzyme essential to the plant’s metabolism, killing most plants within days. Glyphosate was first registered by Monsanto Canada (now Bayer CropScience Canada) in 1976 as Roundup Original Liquid Herbicide, and there are currently over 180 registered formulations in Canada and over 1000 in the United States.

GBHs rose in popularity due to their benefits. Farmers now use less of harmful herbicides, like atrazine, which is acutely toxic to wildlife. Likewise, GBHs decrease the need for weed control by mechanical tillage, reducing soil erosion, wear and tear on machinery, and greenhouse gas emissions. They are also used to artificially mature crops for harvesting, instead of relying on weather conditions, though this is an off-label use not approved by the Canadian government.

Despite the benefits, these herbicides do pose some risks. GBHs may drift in the wind, wash into water, leach minerals from the soil and create GBH-resistant “superweeds,” damaging local ecosystems. Economically, increased MRLs can reduce the exportability of Canadian food products to jurisdictions with stricter regulations. Unusual rates of illness and birth defects have also been linked to glyphosate, however, Bayer maintains that GBHs are harmless when used according to label directions.

In 2015 the International Agency for Research on Cancer (IARC) determined that glyphosate is “probably carcinogenic to humans” after reviewing reports of tumour growth in laboratory animals and “limited…real-world” evidence of cancer in some GBH users. Two years later, The Monsanto Papers revealed the company’s efforts to suppress studies on GBH toxicity, ghostwrite pro-glyphosate scientific papers, and impede safety investigations. Tens of thousands of lawsuits alleging injury from GBHs are now pending. After legal losses totalling more than $215 million, Bayer announced that herbicides for residential use will be glyphosate-free as of 2023.

Despite the controversy, the safety assessments of Health Canada, the U.S. Environmental Protection Agency (EPA), and the European Food Safety Authority (EFSA), as part of their pesticide registration and renewal processes, continue to find that GBHs are safe. For their most recent glyphosate renewals, Health Canada and EFSA relied on similar evidence submitted to the US EPA. Analysis shows that the IARC and EPA conclusions differ for 3 main reasons. First, the IARC focused primarily on peer-reviewed studies, while the EPA concentrated on unpublished, industry-commissioned regulatory reports. Most public studies indicate GBH toxicity, compared to just 1% of industry studies, and the latest EFSA report stating glyphosate and GBHs are “unlikely” to be hazardous had sections copied word-for-word from a Monsanto study. Second, the EPA analysis concerned pure glyphosate, not its formulations, which can be more toxic to humans and animals. For example, polyoxyethylene amine (POEA), a common surfactant in GBH formulations, is 5-times more toxic than pure glyphosate. Finally, the EPA review relied largely on outdated data, while the IARC also considered recent studies on chronic exposures. However, the EPA’s renewal is now under review due to errors in assessing the harms of glyphosate-based herbicides to wildlife and native plants. EU regulations on glyphosate are notably stricter, with lower MRLs and a shorter renewal period (5 years versus 15 in Canada and the US; see Table 1). Several EU members have also enacted additional glyphosate controls, including France, Austria, Denmark, Belgium, and Spain.

Should Canada follow Europe and implement a precautionary approach? While the WHO has stated that glyphosate food residues are “unlikely to pose a carcinogenic risk to humans,” questions remain about the integrity of this assessment. As the vast majority of foods are unlikely to exceed current MRLs, modifications to GBH use, rather than increasing MRLs, would better protect consumers.

We believe there is no current need or justification to increase glyphosate MRLs. An unbiased assessment of the risk to Canadians should be conducted and the government should, beforehand, consider how increasing MRLs could amplify GBH usage and consequently, environmental and occupational exposure.