By Meg Sears, PhD, Chair and Science Advisor of Prevent Cancer Now

How awkward does it get when a chemical company tells one story to the US Environmental Protection Agency (EPA), and another to the patent office? Quite.

EPA registration of Dow’s “Enlist Duo” herbicide mixture was granted in 2014, following no testing of the actual product, and with the skimpiest of margins between levels harmful to test animals and human exposures. The Food and Drug Act 10-fold safety factor was waived on the basis of a “complete and robust” data set for the individual ingredients – glyphosate and 2,4-D.

The assumption is that the toxicity of the ingredients when combined is not greater than those of the individual chemicals – i.e. the whole is no more than the sum of its parts. This default assumption is embedded in US and Canadian legislation. Cumulative exposures are only considered when the mechanisms of toxicity are the same for both chemicals. Unfortunately, just like drug interactions, two or more toxic effects can significantly magnify one another. When toxic effects are unknown or different, diverse pesticides are permitted to be mixed together with impunity.

Although the EPA was not told, according to the manufacturer Dow, for Enlist Duo the “additive toxicity” assumption does not apply to killing weeds.

Key to market protection and to making money is a patent. Products require unique features in order to be patentable, so Dow therefore told the US Patent Office that the two active ingredients in Enlist Duo act in a synergistic fashion (search “synergistic herbicidal weed control from combinations of 2,4-D choline and glyphosate” here). In other words, effects of the mixture are above and beyond simply additive. This came to light during court actions by environmental groups, and the EPA is now wielding its stamp of disapproval, asking the court to reverse registration.

Across North America, constant glyphosate exposures have bred resistance to the herbicide, so “Roundup” (active ingredient glyphosate) is no longer sufficient to kill all the weeds among Roundup-ready crops. Escalating the chemical war, corn and soy seeds resistant to both glyphosate and 2,4-D have been engineered and accepted by the Canadian Food Inspection Agency. Health Canada’s Pest Management Regulatory Agency (PMRA) registered “Enlist Duo” on the same basis as the US EPA, that both individual active ingredients are already registered, with complete datasets.

The International Agency for Research on Cancer (IARC) recently found that in humans glyphosate probably causes cancer, while 2,4-D possibly causes cancer. PCN has summarized concerns regarding glyphosate here and here, and 2,4-D here.

In summary, both 2,4-D and glyphosate are hazardous, and the US Patent Office has been told that the mixture is more than the sum of its parts. Every doctor and patient knows about drug, supplement and food interactions. Every cook knows that “secret sauce” is more than the sum of its ingredients. The US EPA is acting to de-register “Enlist Duo” and we expect no less from the new Canadian government.

Meg Sears, PhD, is an Ottawa-based environmental health researcher and co-chair of Prevent Cancer Now.