small farm

The Road to Probably

small farmLast week, the International Agency for Research on Cancer (IARC) of the World Health Organization announced a summary of a soon-to-be published monograph about organophosphate insecticides and herbicides. An assessment of glyphosate, popularly known as the pesticide, RoundUp®, set the blogosphere on fire.

According to the summary, researchers concluded that glyphosate is “probably carcinogenic to humans.” The use of probably is not my own. That is a direct quote from the report.

The Road to Probably

How did the IARC come to this conclusion? These criteria stand out:

  • Limited evidence of carcinogenicity in humans for non-Hodgkin lymphoma
  • Sufficient evidence of carcinogenicity in experimental animals
  • Evidence of DNA and chromosomal damage in human cells

It’s worth noting as well that “. . . other explanations for the observations (called chance, bias, or confounding)
could not be ruled out.”

The reason is that the findings—for humans, anyway—are based on meta-analysis of observational studies of farm workers and individuals handling/dispensing pesticides. Unlike the lab animals, we don’t experiment with humans. No one is going to volunteer to be in the pesticide application group.

What we’re left with is a distinction between association and causation. Without randomized assignment and sampling of a populaton, science can only find associations, not causes. And that is what makes it problematic.

Confusing to the General Public

Based on the evidence and review, the language of the summary is correct. Science can’t declare something causal without an experiment to control for the confounding factors that may contribute to cancer risk.

Unfortunately, the correct verbiage opens itself to misinterpretation and confusion. Many of the articles I’ve seen reporting on the news have been careful to include the probably part. That’s good from the science perspective; but it’s bad for the general public. In our world, it either does or does not cause cancer. Probably isn’t good enough.

Another thing to bear in mind is the source of the evidence. The human evidence is based on farm worker exposure. The average Joe isn’t going to have the same contact with glyphosate as someone who uses it as part of his job. The other wildcard therefore is the amount of exposure.

As Paracelsus, the Father of Toxicology, reminds us,

“Only the dose makes the poison.”

And that’s where the research needs to go, as problematic as it may seem. In the meantime, it bears mentioning what a pesticide is. A pesticide is “a chemical preparation for destroying plant, fungal, or animal pests.” The findings of the IARC shouldn’t come as any surprise. Chris DR
photo credit: Central Iowa via photopin (license)

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