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Sarah Henderson
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Sarah Henderson
2015-06-18 16:55
Good afternoon.
There is a slide deck for me as well. The first page of that slide deck should say, “Radon risk areas and lung cancer mortality trends in British Columbia”. I hope that you all have it. I will try to speak to the slides as I go along for those who don't have them.
I want to start by saying thank you so much for inviting me to be here. It's a real honour.
My title at the BC Centre for Disease Control is senior scientist, and I'm really a research scientist. The mandate of my role is to conduct applied public health research in support of good environmental health policy for the province, and that's how I first became interested in radon in British Columbia.
I'm going to show you some real, hard numbers today that come directly from the population data for British Columbia, and that's a bit different from what everybody else has been talking about so far.
If you move to the first slide, it's just a recap of the current guideline values for radon in Canada. We've heard about the number 200 all day, and any concentration lower than that is below the Health Canada guideline. Then if you measure your home and the concentration is between 200 and 600 becquerels per metre cubed, Health Canada currently recommends that you try to remediate that within the next couple of years, whereas if your measurement if over 600 becquerels per metre cubed, they really recommend that you remediate right away. That is the high-danger area for radon.
We've used these values in British Columbia to sort of break up the province into areas that we consider to be low, moderate, and high radon areas. If you are not seeing this in colour, the darkest areas there are coloured in red, and those are the high radon areas.
We're very lucky right now in British Columbia. We have a database of over 4,000 residential radon measurements, including measurements from Health Canada national surveys as well as from a bunch of surveys that have happened in the province, so we were really able to use the data that we have observed in the province to break things up this way. These geographic regions are called local health areas. They're the smallest health geographic unit that we use in British Columbia. We are able to look at deaths that have occurred in this province at this geographic scale, which is why we've used this geographic scale.
We did something quite simple, but I hope you'll agree, also quite effective. We looked at the province by those regions, and over the course of 25 years we summed up all of the deaths attributed to lung cancer in the low, moderate and high regions, and all deaths attributed to all natural causes, and then we divided the number of lung cancer deaths by the number of deaths from all natural causes, and in general, we expect about 7% of all deaths in B.C. to be attributed to lung cancer, which is probably true for most of Canada.
Slide number 4 shows the hypothetical situation. If there were no lung carcinogens in the world other than radon, we would expect lung cancer to be high and steady in the higher radon areas, somewhat lower and steady over time in the moderate radon areas, and then lower still and steady over time in the low radon areas. That's the framework I want you to think about when we go to this next slide.
When we looked at all deaths in British Columbia, we saw something quite different from what one would expect to see under that hypothetical scenario. The bottom line there shows the low radon areas. You might not be able to see that if you're not looking at it in colour. The middle line, which is just a little bit higher than the bottom line, shows the moderate radon areas. Then that line that is sloping upward over time and is quite distinct from the low and moderate lines is the lung cancer mortality proportion that we see in high radon areas over the past 25 years in British Columbia.
We don't have a lot of data about these people. We're doing this with only administrative data. We don't know whether or not they smoked. We don't know whether or not they lived their entire lives in those high radon areas. There are a whole lot of limitations here that we simply can't speak to.
When we split up these data by the higher and lower smoking regions of the province—we know that smoking rates can be up to 30% in some areas and down to 12% in some areas of B.C.—we still see these same persistent trends. It does seem to be that radon is an important factor here.
Another important distinction, and I think it's probably why I was asked to be here today, is what we see when we look at the trends for men versus women.
To look at men, the low line shown on the slide is the low radon areas, the middle line is the moderate radon areas, and the top line is the high radon areas. There's not as big a difference among those three lines as there was when we were looking at everybody together. In general, the lung cancer rates are going down. That's what we expect as the population stops smoking. When we go ahead and look at women, as shown on the next slide, we see the low and moderate lines towards the bottom there, and then the line for women is just taking off and is quite divergent from the other regions.
We're seeing a pretty big difference with respect to the two sexes here when we split up these data. Speaking anecdotally, it's not very scientific, but those of us who are interested in radon in British Columbia hear so many stories from people who say, “My wife died of lung cancer and she never smoked a day in her life.” This matches up with what we hear anecdotally, although that's not very scientific.
Somebody asked about the burden of radon-related lung cancer in high- and low-risk areas according to the current Health Canada guidelines. On this next slide, what we see is from data published by Jing Chen from Health Canada. There's an estimate of 6% of the housing stock currently being over the 200 becquerels value, and that's related to 28% of lung cancers in Canada, versus 94% of the housing stock being under the guideline value and 72% of all radon-related lung cancers being attributable to homes in that range. The bulk of the burden really remains below what we're currently talking about in terms of the Health Canada guideline.
This very point is something that we've addressed in a new paper. I want to make it clear that this work has not been published yet. It's currently under review, but it's not in the scientific literature and it has not been peer-reviewed. We looked at a bunch of different threshold values. It's really just a line in the sand that we're drawing when we say that 200 is the level or 100 is the level. We took that line in the sand and drew it at 600, 500, 400, 200, 100, and 50 becquerels to see whether or not we could still see a clear distinction between high and low radon areas in B.C. with respect to lung cancer mortality trends when we drew that line in the sand in different places.
Indeed, if you look at the far right-hand side, that top plot shows you lung cancer mortality trends in men and in women at a threshold value of 50 becquerels per metre cubed, and you can see that the trends are still distinct from one another. We still see that sharp increase in lung cancer mortality in women in the high radon areas.
In the final slide, the key message again is that these are very limited administrative data. This is something we've done as a surveillance exercise. It was really an exercise we undertook because a lot of the evidence we use in Canada to build our policy comes from places other than Canada. We're pulling together studies that have happened in Europe, the U.S., and elsewhere. We really wanted to show some hard-hitting data from the Canadian context.
Again, most radon-related lung cancers in Canada happen below the current guideline of 200 becquerels per metre cubed. We see clear temporal trends by radon risk areas of British Columbia. We have not repeated similar analyses elsewhere in Canada, but I wouldn't be surprised to see similar results. The trends that we see at 200 becquerels per metre cubed persist when we drop that threshold to 50 becquerels per metre cubed. This is really supportive of that idea of ALARA, or “as low as reasonably achievable”. As Tom said, the way to pursue ALARA in Canada is really through widespread changes to our national building code to protect the population into the future.
We have estimated that it would take about 75 years to turn over the entire residential building stock in Canada, or most of it, but at the end of that 75 years, you would have a radon-resistant building stock and a population that was well protected.
Finally, there does appear to be a difference between men and women in terms of risk.
Thank you very much for your time.
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