Friday, February 6, 2015

How Big and Small Numbers Influence Science Communication Part 3: Understanding "Acceptable" Risk

In my last post I wrote about the basic concepts of toxicology including dose/response relationships and the concept of a de minimis risk. Today I am going to expand on that concept by discussing what represents an “acceptable risk” in the risk assessment world and how that information is mis-communicated on a daily basis.  

If you are like me, you often watch the news and get frustrated by the NIMBY’s on the screen describing why this development should be abandoned and why that technology should not be trusted. Be it WiFi, oil sands or radio towers, nine times out of ten, one of the terms they will pull out of their hat is “the Precautionary Principle”. In their minds the Precautionary Principle is some magic bullet that will silence all opposition. My response is to slightly misquote Inigo Montoya from “The Princess Bride”: “You keep using that term, I don't think you know what it means”. You see the Precautionary Principle does not actually say what most of these activists seem to think it does. The actual Precautionary Principle was defined as Principle 15 in the Rio Declaration which states:  

"In order to protect the environment, the precautionary approach shall be widely applied by States according to their capabilities. Where there are threats of serious or irreversible damage, lack of full scientific certainty shall not be used as a reason for postponing cost-effective measures to prevent environmental degradation.”

The Precautionary Principle does not say that all risk is bad risk and that all risks must be avoided because that is not a realistic way to run a society. Getting out of bed in the morning poses a non-zero risk of slipping and breaking your neck. Using the activist view of the Precautionary Principle we would have to ban all beds to avoid that potentially fatal risk. Instead of requiring “no risk” in the real world we ask: what is considered an “acceptable risk”? Not surprisingly, this question has been posed by many over the years and lots of research has been done on the topic. After much debate and discussion a consensus has been built as to what actually would be considered an “acceptable risk”. The generally accepted guidance is provided by the USEPA and shared by Health Canada and the BC Ministry of Environment:

For known or suspected carcinogens, acceptable exposure levels are generally concentration levels that represent lifetime cancer risk to an individual of between 10-4 (1 in 10,000) and 10-6 (1 in 1,000,000) using information on the relationship between the dose and response. The 10-6 risk level shall be used as the point of departure for determining remediation goals (ref)

So for a carcinogen, that involves a concentration that when administered to one million people, continuously (24 hours per day) over 70 years (an assumed lifetime), would result in one additional case of cancer in addition to any cancer that might occur in a person not exposed to the compound. Frankly, I can’t imagine getting much more conservative than that. The activists say that the health authorities are being insufficiently cautious but it is pretty clear by that definition that they are in fact being incredibly cautious. For non-carcinogens we can calculate a “Hazard Quotient” which the BC Government defines as

Hazard quotients are calculated for substances that do not cause cancer. A hazard quotient is the dose of a substance received from a site (the estimated daily intake) divided by the safe dose for the substance (the reference dose). (ref)

A reference dose, (RfD) is a concentration or dose of a compound in question to which a receptor may be exposed without causing adverse health effects (i.e. a dose that is considered “safe” or “acceptable”). Using the terminology from our last post it would be the no observable adverse effects level (NOAEL). Under the current British Columbia regulatory regime a hazard quotient of 1 or lower is considered to pose an acceptable risk. That is, if you have an NOAEL of 10 for a compound, then any concentration below 10 would be considered acceptable as it would not be expected to expose a receptor to unnecessary risk. So once again we have a concentration that is demonstrated to not have the ability to cause harm.

Let’s consider now what all these numbers mean and to do so let’s use one of my favourite examples: WiFi units in our schools. Not too long ago there was an intense lobby to try and remove WiFi units from selected schools. The activists played all the familiar cards. First they argued that WiFi as a “new” technology had not been well studied and thus posed an unknown (and therefore potentially excessive) risk. This, of course, is baseless. WiFi is based on microwave technology and microwave technology is neither special nor unique. It has been widely used for decades and the research in the field is deep and varied. The next approach was to attack using a “big number versus small number approach”. We all know that microwaves are dangerous at high power, after all we use them to cook all the time, so they must be dangerous at lower doses. As we've discussed previously it doesn't work that way. Microwaves represent non-ionizing radiation that can be absorbed by water molecules resulting in thermal effects. What this means is that it does not have the energy to remove electrons from atoms/molecule and thus does not damage DNA etc.. Microwaves work by heating. At high power they can indeed cause damage to human tissue, which is why it is a bad idea to climb an active microwave tower. But a WiFi unit lacks the power to heat a thimbleful of water, let alone a human body. Putting on a hat provides orders of magnitude more thermal energy than a WiFi unit attached to your head could. The final complaint is that Health Canada “safe” levels might be too high. But as we just learned the levels are actually incredibly conservative and exposures to concentrations much higher than allowed by Health Canada would still not cause an issue.

This is the playbook, it is used on WiFi, on pipelines, on bitumen, essentially on any topic where doubt can be spread about. In my next post, I'll go into how risk assessors actually work to establish whether a risk is something to worry about.


  1. I can't wait to read your next post on the hazards of bitumen. I assume this will be the mythical oil spill reaching the Oglallala aquifer?

  2. I'm sorry to tell you, but "principal" and "principle" are quite different words, and you appear to have chosen the wrong one ;(

  3. You are right and I have egg on my face. Thanks for the catch