RE: Chromosome aberration study

[Keith Welch <welch@jlab.org>]

Franz wrote:



>This may be of real interest to the group.

>

>

>> Dr. Elza Sakamoto-Hojo from Universidade de São Paulo in Brazil and

>colleagues compared chromosomal aberrations, sister chromatid

exchanges,

and

>micronuclei in lymphocytes from eight hospital workers chronically

exposed

>to ionizing radiation (accumulated absorbed doses ranging from 9.5 to

209.4

>mSv) with those in eight age-, sex-, and smoking habit-matched

individuals

>not exposed to ionizing radiation.







When I started to read I became at once suspicious: "Low-Level Exposure"

-

how is it defined? When I recognized it was on hospital workers I could

imagine that the term "Low-Level Exposure" in the context of this

article

would be quite different from what LNT pro's and con's discuss about.



Let me make it clear: I am far from being an expert on this topic, but I



miss in this posting some information. First of all the time span during



which the accumulated absorbed doses were received. Is it per year, per

month, per week or during five years? I believe that this is very

important.

Now, let us assume that it is per year. 9.5 mSv is in my perception not

low-level but if we assume a low background area it would be about four

times the usual natural background in addition to it. Such persons are

clearly radiation workers according to the limits in the European Union.

A

dose of 209.4 mSv accumulated during one year would be a very severe

criminal offence in the European Union, because in almost all countries

of

the EU the maximum permissible yearly dose to a radiation worker is 20

mSv,

which might be exceeded in one year up to 50 mSv, but has to be in any

case

below 100 mSv within five consecutive years. If the 209.4 mSv would be

accumulated during let's say 50 years of profession, then it might under



average conditions correspond to twice the background dose and not be of



concern.



So, these are my problems with such articles or their citation. Do you

have

any information about the yearly doses?



Franz

----------------

Franz,



I would think most people would consider these doses to be low level.  I

think the authors said these were

cumulative exposures - which I assumed to be total life-to-date.  And

even if it weren't, it is still in the

range generally called "low level" (although above limits).  I was

shocked by the report for different

reasons. My questions are (and I'm no geneticist).....



- I thought chromosome aberration was undetectable below something like

25 rem - and that the only way to

detect it at that level was with a "pre-dose" measurement of the

abberation rate in that individual.  I had

presumed that variability was so large in this range that differences on

the order of those described were

not statistically significant. This some new method that is

super-sensitive?  I thought previous sensitivity

was sufficient enough to determine that there was no significant

increase at this dose.

- It's not clear how the data are "grouped".  There's a significant

range in dose, but the result is not

dose-related - it's just a general outcome that says if you're "exposed"

you have this "average" increase.

Is the highest exposed individual showing any higher aberration rate

than the lowest?  If not, what would

lead to the conclusion that the aberrations have anything to do with

radiation?  This would support the idea

that genetically, 'any' dose is as bad for you as a large dose.  One

mrem is all it takes to foul up your

chromosomes forever.

- Eight people?  Come on.  Why not 800?  If this type of dosimetry is so

great, let's do it on a large number

of workers and see what we get.  And speaking of that....

- Is this method known to be accurate with the precision necessary to

get the results stated.  Is it really

"dosimetry"?

- "New rules" based on this?  A little premature, don't you think?



--

Keith Welch







************************************************************************

You are currently subscribed to the Radsafe mailing list. To unsubscribe,

send an e-mail to Majordomo@list.vanderbilt.edu  Put the text "unsubscribe

radsafe" (no quote marks) in the body of the e-mail, with no subject line.