Seraph, a little harsh, but arguably deserved. I should provide sources when I make an argument.
So here are my sources:
EPA's health assessment of Asbestos. Of particular note here is that they acknowledge that there is no scientifically established level of exposure. Elsewhere on the EPA page, they explain that the studies used in preparing the standard did not specify exposure levels, thus, they did an educated guess to arrive at the exposure limit. They estimated a limit of 0.23 fibers per ml, and an estimated one-in-a-million increase in risk at 4 fibers per ml. (Note that the text on page 3 is in error. On page 4, they correctly listed the estimated risk assessment, consistent with the figure listed by their source document.)
Also note that on page 4, there is a much lower threshold for crocidolite, the African asbestos, than for crysotile, the more common form used in the US (other than in WWII shipyards), and is the form that is mined in Canada and several locations in the US.
http://www.epa.gov/asbestos/health.pdf
My second source was an article in Washington Post from several years back, but since I assume most of you are not subscribers, I searched Google for a copy of the article elsewhere. Interestingly enough, it popped up in a page on a site called junkscience.com.
Of note here is that instead of the usual methodology used in the other studies, which was to see what fraction of mesothelioma patients had exposure to asbestos, these Canadian researchers looked at people who were exposed to asbestos and compared those cancer rates to cancer rates in unexposed populations. The upshot is that they were not able to identify an increased risk, though they were exposed to asbestos at a rate that should have been unmistakable if the EPA guesstimate of exposure risk was within an order of magnitude.
I'll save a discussion of why this methodology is the correct one for the next source.
http://www.junkscience.com/news2/wpasbest.htm
Thirdly, I would refer you to a book called
How to Lie With Statistics by Darrell Huff. There are several similar books but most are pretty hard to understand if you do not do experimental design for a living. This one is probably one of the more readable explanations of how studies with the wrong methodologies usually arrive at the wrong answer. He uses several examples to illustrate the faulty methodologies used not only in asbestos studies, but in several chemical scares, like DDT and Alar.
The basic idea is that you cannot take a particular subset of data and extrapolate it to the population in general, unless you can make sure that the subset is representative of the general population
in all other respects. A good example is the "marijuana is a gateway drug" myth, because it merely asks heroin users whether they smoked pot before using heroin. The correct methodology would have been to look at long-time pot smokers and see how many moved on to harder drugs.
There is no question that at high levels of exposure asbestos is bad stuff, and little question that it is linked to higher rates of lung cancer and mesothelioma. There is a question, though, of what constitutes a high level.
The Canadian study, as well as the asbestos in the air following 9/11, is a big reason that EPA's CRAVE group is doing a major review of asbestos, with a view of trying to establish some better data, but early results leaked to Wall Street Journal a couple months ago indicate that the exposure limit will probably be relaxed by at least a factor of 10.
[ 03-28-2003, 12:50 PM: Message edited by: Thorfinn ]