Good evening, Dr. Zoomie – I came across a YouTube video the other day that was most fascinating; it was about how we respond to low levels of radiation exposure – whether or not every little bit of dose might put us at risk. There were some knowledgeable gentlemen who spoke quite convincingly on the subject. May I ask your opinion on this video?
Ah – radiation safety’s Never-Ending Story! The debate over the how small radiation doses might affect our health goes back nearly a century; the current paradigm (that the risk from radiation exposure is directly related to the amount of exposure, no matter how low that exposure might be) was first proposed about 80 years ago. And in that time, while we’ve learned a tremendous amount about the health effects of radiation exposure, we’re still using the same Linear, No-Threshold (LNT) model to describe how radiation affects us. And what’s remarkable about this video is that David Brenner, a scientist at Columbia University and a staunch proponent of LNT for decades, talks about why he no longer believes it’s an accurate description of how radiation exposure affects our health under some circumstances.
But before we get into Brenner’s change of heart, let’s look at why this debate about whether there can be a safe dose of radiation might or might not matter.
Playing the lottery: Let’s say I’m doing something that has one chance in a million of being fatal. Those odds are pretty good – 999,999 chances I’ll live and 1 chance that I won’t…I’d take those odds. And I can state that from actual experience – over my lifetime the chances that I’ll die in a traffic accident are a lot higher than one in a million; over my career the risk that I’ll die of an occupational illness or injury is far greater…I could go on (and on and on), but you get the idea. The same reasoning is why I don’t play the lottery – the odds against me are so high I just can’t justify buying a ticket. And yet, there’s a winner almost every week. If enough people take even a very low risk, there’s a reasonably good chance that one of them will get bit by that risk. I live in NYC – if something happens that’s fatal to one person in a million then 8 or 9 New Yorkers can be expected to succumb. This is where the emotional part of our brains can go to war with the logical parts, and this is why the hypothesis matters. With LNT, we’re playing the lottery and no matter how steep the odds are of my getting sick from a radiation exposure, I might hit the lottery (as it were). But if there’s a threshold, below which there’s no risk…well, there’s no risk because there’s no lottery. And psychologically, there’s a huge difference between a very, very small risk (you never know) and zero risk (it literally can’t happen).
Managing a radiation safety program: Having said that, I’ve managed radiation safety programs in the past and I’m managing one now. If there’s a threshold dose below which radiation poses no risk it’s quite possibly somewhere around 10 rem of lifetime exposure. With an average lifespan of, say, 80 years that means that I should try to keep radiation exposure to the public to less than 125 mrem annually. Round that down a little to give a cushion and we’re at about 100 mrem of dose annually to non-radiation workers. Which is exactly what the dose limit for members of the public happens to be. So, fascinating as the debate itself might be, the answer isn’t going to affect the way that I practice radiation safety. From this perspective, the answer just doesn’t matter.
The scientific debate: That being said, there have been a lot of scientific debates that have absolutely no impact on how any of us live our lives and work. But even if the public don’t care, scientists do care – and many of them care deeply. Consider – were many lives uprooted in the 19th century when it was settled that there really was a geologic time period called the Devonian sandwiched between the Silurian and Carboniferous periods and ending nearly 360 million years ago? My BA and MS are in Geology and I have to admit I’ve never given this controversy much thought and whether there is or is not a Devonian period has had no impact on my life. But for a small subset of geologists this controversy and how it was resolved – as well as all of the less-controversial work of pinning down exactly when the various geological periods began and ended – is hugely important. And let’s face it, answering these questions gives humanity a better understanding of our planet, its history, and the history of life on Earth. With LNT, even if resolving the matter isn’t going to affect my professional or personal lives, the question remains a fascinating one and I’m curious as to how it will all end up.
That’s how I look at it – you’ve got to decide for yourself whether you’re curious, concerned, or don’t really care all that much.
Going back to the video, Brenner made some interesting points, and the way he looks at the matter is a lot different from the way that I do. Using a machine learning program, Brenner’s new analysis of radiation exposure data seems to tell him that there’s no discernible health effects from exposure to dose less than 5 rem. Brenner also points out that early models were based on atomic bomb survivors, who were blasted with a high dose of radiation in a fraction of a second, while most radiation workers receive low doses of radiation over a lifetime – sort of like noticing that there’s a difference between throwing a million pebbles at a person over their lifetime and dropping a ton of gravel on them all at once.
Will this change your life? Well…probably not. But Brenner’s been a big proponent of LNT for a few decades – seeing him apparently change his thinking speaks well for him as a scientist and it makes me want to learn about his machine learning work. I’m not sure that this will revolutionize our understanding of radiation and its health effects – but I wonder if it percolates out to the public that they’re not “playing the lottery” in which there’s a chance (however small) of hitting the “jackpot” – rather, they’re playing a game that’s rigged so they can never win unless they get a higher dose even higher than what most radiation workers receive. If so, maybe more people will start worrying (and caring) less about the subject.