Re: Fed Express worker received 1.5 rem from Ir-192 source

["Bjorn Cedervall" <bcradsafers@HOTMAIL.COM>]

>Can anyone out there (someone from REACTS?) tell us how clinicians can

accurately measure exposure to 1.5 rem based on blood tests (lymphocyte

chromosome aberrations?). If the worker is about 25 years old, his/her

lifetime dose has to be close to or above 7 or 8 rem anyway.  I thought

that "natural exposure" would contribute to enough chromosome aberrations 

that dose estimating is difficult below 5 or 10 rem.

---

If the dose reconstruction is based on chromosome aberrations I guess a 

couple of different approaches can be imagined:



1. Counting the frequency of micronuclei (has been shown to work 

statistically down to a level of about 2.5 mGy/day, ref. L. 

Abramsson-Zetterberg, J. Grawé et al., Int. J. Radiat. Biol., Vol. 67, 

1995:29-36 see also other works by the same group. BTW: the induction of 

micronucleated polychromatic erythrocytes (MPCE) shows a statistically 

significant straight line with increasing dose).

A question is: What frequency of MPCE:s did the individual have before the 

exposure (you can only be your own "control group"). As erythrocytes are 

formed continuously I guess that a follow-up that reflects the time kinetics 

(days-weeks-up to perhaps as much as 1-2 months) will show where the base 

level is for the particular individual. If I interpret the works by 

Zetterberg-Abramsson et al. correctly, most detectable of X-ray induced 

MPCE:s (in mice) disappear within a week.



((An "EMF application" of the technique can be found in the following work 

from: Bioelectromagnetics 2001 Jul;22(5):351-7.



Extended exposure of adult and fetal mice to 50 Hz magnetic field does not 

increase the incidence of micronuclei in erythrocytes.

Abramsson-Zetterberg L, Grawe J.



Department of Environmental Toxicology, Uppsala University, Uppsala, Sweden.



The flow cytometer-based micronucleus assay was used to study the effects on 

chromosomes in erythroid cells of CBA/Ca mice after extended exposure to 50 

Hz magnetic field (MF), 14 microT, peak-to-peak (p-p). The study included 

two different experiments: (a) mice exposed in utero during 18 days of their 

prenatal stage, and (b) adult mice exposed for 18 days. In experiment (a) 35 

days after exposure was terminated, peripheral blood was drawn from the mice 

exposed in utero to determine whether the exposure had a genotoxic effect on 

the pluripotent erythroid stem cells. About 200000 polychromatic 

erythrocytes (PCE) and 200000 normochromatic erythrocytes (NCE) were 

analysed from each of 20 exposed mice. The EMF exposure did not 

significantly change the frequency of micronucleated PCE or NCE in 

comparison with 20 sham-irradiated mice. There was no difference in the 

proportion of PCE between exposed and unexposed animals. Similarly, in 

experiment (b) no differences were seen between EMF exposed and unexposed 

adult mice when samples of peripheral blood were taken at the end of 

exposure and analyzed for micronuclei in PCE and NCE. The proportion of PCE 

was the same in both groups. The results indicate that exposure to EMF does 

not induce direct or indirect effects on chromosomes in erythroid cells 

expressed as increased levels of micronucleated erythrocytes of mice. No 

indications of delayed genetic effects were found. Copyright 2001 

Wiley-Liss, Inc. ))



2. Counting specific chromosomal aberration frequencies and comparing ratios 

between different classes of aberrations and how these ratios change over 

time. Some of these appear with time, others are stable for very long 

periods. As a result of individual variation in radiosensitivity relatively 

large uncertainties (statistically perhaps in the order of +/- 50 %?) can be 

expected.



My guess is that the MPCE method (or both approaches) was used - perhaps 

some Radsafer can confirm. The majority of the background induction of 

damage from the previous say 25 years has been repaired or the affected 

cells have died. The chromosme aberrations that can be seen after 25 years 

must be a very small fraction (much less than 1 %, my guess) of the total 

induced over that time.



My personal reflection only,



Bjorn Cedervall    bcradsafers@hotmail.com





_________________________________________________________________

Chat with friends online, try MSN Messenger: http://messenger.msn.com



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

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.

You can view the Radsafe archives at http://www.vanderbilt.edu/radsafe/