Comment at bottom.
At 3:36 AM +0000 12/2/02, olympus-digest wrote:
>
>Date: Sun, 1 Dec 2002 13:02:21 -0800
>From: Winsor Crosby <wincros@xxxxxxxxxxxxx>
>Subject: Re: [OM] Lens cleaning (acetone a carcinogen?)
>
> >
> >
> >Trichloroethylene (TCE) has in the last few years been reclassified
> >as a class 2 carcinogen, which means that various exposure-reducing
> >precautions must be taken when it is used. TCE has not been banned
> >from industrial use, but at least in the US it may no longer be sold
> >to the general public. The major exposure-causing use is in the
> >vapor degreasing of metals, a process using many gallons of solvent
> >in an open-top boiler-condenser rig. There are millions of such
> >rigs, but liver cancer isn't all that common, even among workers
> >exposed daily. Despite all the hysteria now surrounding the subject
> >
> >None of the common solvents, even those now known to be carcinogens,
> >are dangerous enough to be a problem for incidental users.
> >Something else will kill us first.
> >
> >Joe Gwinn
>
>How do you know this? Are you a health professional?
I'm not a doctor, but I do follow the debates in Science, Nature, The Wall
Street Journal, et al. It's hardly a secret.
>I have known as many people to die from liver cancer as any other kind.
>Of course there are many known causes of liver cancer such as alcoholism and
>hepatitis infections.
You've hit the nail on the head. Alcoholism and hepatitis infections are far
more common than heavy exposure to solvents. (My kid sister's first husband
died young, of hepatitis.)
How do I know that the risks of solvents are low? Because all these solvents
were widely used industrially for decades, and yet the streets were not
littered with the dead and dying, so whatever the effect it cannot be very
strong an effect. And, because it was only after decades of debate were some
uses of these solvents restricted -- the various health effects were debatable
to slight, taking many decades of experience to build a statistically adequate
case. And this is for people who use large amounts of the sovents every day,
not incidental users.
The reason to restrict access by incidental users is basically statistical
cost-benefit, albeit based on a questioned extrapolation. Basically, suspected
carcinogens are tested by making rats live in high concentrations of the
candidate stuff, and then extrapolating the kill rate linearly down to very low
doses. There are two major problems with this, but the method is used for lack
of a better method, as the debate rages. The first problem is that rats are
not humans, and yet we are extrapolating rat toxicity to humans. This mostly
works, but there are a number of substances that are known to be toxic and/or
carcinogenic in one species but not the other, in both directions. Second is
the linear extrapolation to low doses: Most, perhaps all, substances show a
threshold dose below which there is no effect whatsoever. However, it takes
experiments of very long duration with very large numbers of animals to explore
this, so there are few results yet available. These exper!
iments are very expensive to run, and take longer than the usual academic
career to complete, so it's difficult to find Principal Investigators to
undertake such experiments.
Anyway, the thinking is that weak carcinogen X will still cause a significant
number of cancers in a large population, even if the individual risk of cancer
is very low, so as a matter of public health, it's better to restrict X, unless
there are no practical alternatives to X. Naturally, this triggers a fierce
debate on the actual practicality of the proposed alternatives to X, not to
mention the above-mentioned logical flaws in the entire enterprise.
Joe Gwinn
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