Cancer: Risk vs. Hazard

Thursday, October 27, 2016

This morning, I ran into an article that raised my hackles for a moment, regarding claims by an agency of the World Health Organization (WHO) that gyphosate (known commercially as RoundUp) is "probably carcinogenic." In the lead-up to the meat of the article the following made me stop cold (The article concerns legal maneuvers by the manufacturer in relation to documents relevant to that assessment.):

In recent years IARC, a semi-autonomous unit of the WHO based in Lyon, France, has caused controversy over whether such things as coffee, mobile phones, red and processed meat, and chemicals like glyphosate cause cancer.

Its critics, including in industry, say the way IARC evaluates whether substances might be carcinogenic can cause unnecessary health scares. IARC assesses the risk of a substance being carcinogenic without taking account of typical human exposure to it. [bold added]
What? My mind immediately protested. Something is definitely wrong here, but it isn't exactly what I was thinking.

In attempting to dig into what might be going on -- bad science? bad reporting? -- I discovered that Derek Lowe, one of my favorite scientific bloggers, addressed this matter months ago. In particular, he passes along an analogy concerning risk vs. hazard:
A toxicologist interviewed in the Wired article makes a great analogy to explain hazard versus risk, which is what we're talking about here. Sharks are a hazard. They are fierce predators with sharp teeth, and they most definitely have attacked humans in the past. But for most people, sharks are not much of a risk. "Risk", technically speaking, refers to your chances of being harmed under real-world conditions, while "hazard" refers to the potential for harm. A large shark has plenty of potential to do damage to you, but should you be worried about that happening? It depends. If you're sitting in your car, probably not (you have other, more immediate risks to worry about). If you're swimming off a tropical beach, though, that may be another matter. And if you're doing so after cutting your foot and leaving a trail of blood in the water, I would seriously consider the shark possibility and act accordingly: your risk has increased to what most people would find unacceptable levels.

Fine -- but what about your risk when, say, you visit an aquarium? Remember, the hazard a shark poses has not changed during all this -- he's still hungry and he still has a mouthful of teeth. The shark is the shark. Your risk of being bitten by him has, in fact, increased a great deal when you visit an aquarium -- you've gone from a place (your home, your car) where there are (one assumes) no sharks whatsoever, and now you're in the same room with one. True, you're separated by a thick pane of glass, and true, it's hard to come up with a plausible chain of events that would lead to said shark chomping on your leg, but it's undeniable that this is much more possible than it was in the parking lot outside the aquarium or back in your bed. The odds are still vanishingly low, and not many people worry on their visit the aquarium about the chances of being bitten by a shark (nor should they) -- but if you write things up from the right angle, that visit can look wildly dangerous. "RISK OF SHARK ATTACK NOW INCREASED BY FACTOR OF ONE MILLION!"
Considering the first quoted passage again, it is not necessarily bad science to evaluate whether something might cause cancer in isolation from how much exposure someone might normally receive. But it would be irresponsible, when reporting such an assessment, not to make clear that the level or likelihood of exposure matters regarding how likely someone might be to contract cancer from the substance. And it would be bad journalism to gloss over such a distinction (assuming it is made), or not to seek clarification, given the widespread use of RoundUp over decades absent a concurrent "epidemic" of cancer.

The interested reader will find much more about the risks and hazards of RoundUp at the blog post I mentioned above, which is an oasis of sanity compared to much of what I have seen and heard about RoundUp over the years.

-- CAV

P. S. It is interesting to note what Bruce Ames, who invented a screen for possible cancer-causing substances, has to say about things that might cause cancer:
He argued against the banning of synthetic pesticides and other chemicals such as Alar which have been shown to be carcinogenic. He was concerned that overzealous attention to the relatively minor health effects of trace quantities of carcinogens may divert scarce financial resources away from major health risks, and cause public confusion about the relative importance of different hazards. Ames considered himself a leading "contrarian in the hysteria over tiny traces of chemicals that may or may not cause cancer", and said that "if you have thousands of hypothetical risks that you are supposed to pay attention to, that completely drives out the major risks you should be aware of." [links and notes dropped]


jacobeking said...

Thanks for linking and discussing this article. The military uses very specific definitions of hazard and risk.

A hazard is a situation which can result in harmful effects if allowed to proceed unchecked. It is classified according to the severity of its effects. Risk is based on a combination of severity and the probability of encountering the hazard in one's planned activity.

It's amazing how many people there are (at least in my line of work) who can recite those definitions but fail to apply them properly. You frequently find managers interested in protecting against all sorts of high-severity, yet highly improbable risks.

Gus Van Horn said...


It's not just definitions for many people. I am regularly flabbergasted at how many people fail to recognize how even perceptual-level (or nearly so) facts can and should affect their opinions. I blame "progressive" "education" and the philosophic influence of pragmatism for most of the problem, although there will always be people who can't or won't make even obvious connections.