Radioactive Times: LLRC Journal

New study of internal contamination shows higher risk

report from Radioactive Times Volume 3, Number 1, March 1999E (content not updated)

Another research study has been published that suggests that internal radiation exposure from man-made isotopes results in higher risk of cancer. [Carpenter 1998].

It follows a number of studies which continued the investigation into the effects of internal isotopes on prostate cancer in nuclear employees by Valerie Beral et al. The earlier paper found high relative risk of prostate cancer, up to 20 times the expected rate, in nuclear workers monitored for internal exposure. The present study looked for effects in all cancer sites.

The total number of radiation workers involved was 40,761 of whom about half, 23,156, had not been monitored for any radionuclide.

Sigificant excess

The results showed that overall cancer death rates were significantly lower than those expected on the basis of national rates (SRR = 80), but since the workforce generally has a lower death rate for all causes (SRR = 80) owing to better health (healthy worker effect) this was not surprising. Employees monitored for internal contamination had slightly higher cancer rates than those not monitored. Rate Ratios (cancer rates for those monitored vs. those not monitored) were significantly higher in the case of the following cancer sites: cancers of the bronchus and lung, liver and gall bladder, larynx, uterus, ovary, testis, prostate, non-Hodgkin lymphoma and multiple myeloma.

A significant excess of prostate cancer was confirmed for an association with Tritium (RR = up to 3.19) and other radioisotope monitoring (RR = up to 2.06). For all malignancies, the results seemed to depend on the period of exposure, or at least the time since first monitoring. There was a strong association between Plutonium monitoring and lung cancer mortality.

Statistical fiddle

The authors appeared to minimize the findings in a number of ways, and their use of two-tailed significance tests in this situation is extremely questionable since only positive effects were being sought. Nevertheless, there was quite definite evidence of excess risk from internal contamination. Similar effects were clear in the earlier record linkage study (RaT 2/3, p. 4) which showed higher leukemia risks in offspring of radiation workers who had been monitored for internal radionuclides compared with those who had not been.

Of course, the real problem is that we do not have information about the speciation and concentration of the internal nuclides. Nor are we even certain that someone who has been monitored has actually been contaminated. We do, however, know that the controls, all of England and Wales, have also been contaminated, from weapons fallout, Chernobyl, Sellafield, and so forth. Table 1 shows the Plutonium contamination of members of the public (predominantly from Sellafield)

Tissue (post mortem) Cumbrian workers
(Figures given for each of three cadavers in mBq/Kg Pu)
Cumbrian public
(mBq/Kg Pu.
Figure in brackets is number of cadavers)
Public elsewhere
(mBq/Kg Pu.
Figure in brackets is number of cadavers)
Rib 130
360
94
9 (10) 6 (43)
Femur 132
250
100
5.4 (11) 3.6 (35)
Lung 940
1140
120
6.8 (11) 1.9 (47)
Tracheo-bronchial lymph nodes 450
73,300
1600
35 (12) 10 (37)
Source Popplewell/ NRPB 1986
and Figure 2 below shows Plutonium in children’s teeth.
(12KB) Log. concentration of Plutonium in children's teeth by distance from Sellafield (mBq/Kg) Source Priest et al. 1997.
It is instructive that the levels fall off steadily with distance. Would NRPB suggest that there is a linear relationship between the distance of our homes from Sellafield and the rate at which we eat shellfish and lobsters caught in the Irish Sea? The more likely explanation is that nanometre sized particles are blowing ashore, and are resuspended by the electrical charge that accumulates on the particle. Each particle is then blown further inland, resuspended again, and again, and again, until someone swallows it. When they die they are cremated, and the hot particle, unchanged physically and still giving off the same dose, is released into the atmosphere once more.
Thus again we see that the problem with nuclear worker studies is the lack of uncontaminated controls And even the measurement of radioisotopes in people is difficult when they may be in the form of ‘hot particles’ as with the Plutonium particles scavenged from the lung to the bronchio-thoracic lymph nodes (see Table 1 and picture on our Home page).

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