Re: Rn, Epidemiology + thoron

[Kai Kaletsch <info@eic.nu>]

Good point!



World average thoron concentrations are not relevant. There is a huge

variation in average Radon/Thoron ratios according to region. It depends

mainly on the uranium/thorium ratio in the soil.



Short lived thoron gas usually doesn't contribute much to the reading on a

residential radon GAS detector, but the longer lived progeny can build up

and give a lung dose. I would make the following observations:



1.    Depending on the region, the presence of thoron can severely affect

your exposure assessment. (Does not necessarily bias to the null, because

radon and thoron levels are related.)

2.    The argument that a radon gas reading is more representative of actual

dose than a radon progeny reading is affected by the presence of thoron.

3.    Possible systematic relationships between lung dose and smoking are

enhanced, if your dosimetry is based on gas (not progeny) measurements.



Kai





----- Original Message -----

From: "Yarmoshenko IV" <ivylist@ECKO.URAN.RU>

To: "RADSAFE" <radsafe@list.vanderbilt.edu>

Sent: Friday, February 15, 2002 1:39 AM

Subject: Rn, Epidemiology + thoron





> Dear Radsafers,

> At first, let me thank those of you who began and continue

> the discussion on the radon epidemiology. On my opinion it

> is very important and essential topic. The apparent conflict

> of some studies' results (sure, No 1 is B. Cohen's) and LNT

> attracts great attention and bothers all specialists in the field

> of radiation protection.

> The arguments against ecological study design itself are still

> unconvincing, though case control design is preferable. It is

> clear that due to statistical power each of the case control

> study along couldn't reject or prove LNT in the radon

> concentration interval of interest. So, the pooling of

> different case control studies should be undertaken. Last

> meta-analysis have been published in 1997 (Jay Lubin and

> Jhon D. Boice, Jr.), it included eight studies (4263 cases and

> 6612 controls). Since 1997 the list of radon and lung cancer

> case control studies have broadened up to 18 (at least)

> and now includes about 11 000 cases and about 19 000

> controls (my assessment). I believe new meta-analysis could

> be performed quickly.

>

> Another point which I would like add to the discussion is

> thoron. Usually researchers doesn't consider thoron progeny

> exposure at all (both in case control and ecological studies).

> I think it is not quite well-founded. According to

> UNSCEAR Report world average thoron equilibrium

> equivalent concentration is 0.3 Bq/m3 and range of average

> concentration by surveys is 0.2-12 Bq/m3. These values

> seems to be negligible. But I think it is negligible for

> radiation protection purposes but not for epidemiological

> studies. Exposure to 1 Bq/m3 of thoron EEC is equivalent to

> about 12 Bq/m3 of radon concentration (1*5/0.4). Such

> thoron EEC can substantially change the distribution of

> subjects by intervals of exposure, especially in low range of

> exposure, and consequently bias the results.

>

>

> Ilia Yarmoshenko

> Radiation Laboratory

> Institute of Industrial Ecology

> Ekaterinburg

> Russia

>

>

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