Radiation Protection Science - NRPB flannels about hot particles

NRPB flannels about hot particles

In public meetings recently NRPB has tried to answer public concern about the impact of hot particles by claiming that this had been investigated and dismissed twenty years ago -
the effects of hot particles in the lung were no greater than the effects of the same dose averaged out across the lung, said Dr Edwards.
LLRC has obtained the 1983 research paper they were referring to (1).

The insane experiments it describes in no way even investigated the hot particle problem, let alone disposing of it.

Rats were made to inhale particles of oxides of enriched uranium. Doses from this source were very high. In addition, some of the rats were also put inside a nuclear reactor to expose them to huge doses of slow neutrons.
A control group inhaled the Uranium but were not put in the reactor.

The first point is that this was not a study of the effects of hot particles; the main aim was to find out the effect of the neutrons interacting with the enriched Uranium -- they would make it behave like uranium in a reactor, giving off charged particles of all sorts.
For this reason a second control group inhaled the Uranium but only after being put inside the reactor.

Second point: while the "uranium only" rats lost 6% of their life expectancy,
all the rats exposed to Neutrons lost at least 17%, while the ones who went into the reactor before inhaling (so they didn't get turned into mini reactors) lost 20%. [
Some results are presented at the foot of this page]
The amount of life-shortening was not related to the Uranium dose. So what does all that tell us? It means that high doses of Neutrons are bad for you.
Nothing more. Big surprise; we don't think!
[Unfortunately, no-one seems to have thought of having a control group exposed to the Neutrons but not the Uranium.]

Third point: these were huge doses -- comparable with the killing dose as identified by the Hiroshima studies. Nothing to do with the very low "whole body" doses we might get from inhaling hot particles and getting them stuck in our lymph nodes.

Fourth point: this study is about lung tissue; it says absolutely nothing about lymph nodes. [ICRP treats lymph nodes as "a region of the lungs", but that doesn't mean they are a region of the lungs -- they have a completely different structure and a completely different function:

Fifth point: The study estimated radiation effects by counting primary neoplasias (cancers).
A weakness of the study was that it tended to underestimate the hot particle effects by discounting multiple cancers of the same type in the same animal.
Nevertheless, the highest rate of primary neoplasias was found in the high dose "Uranium only" rats -- 66.6% of them had primary cancers when killed, compared with 10% in the low dose "Uranium only" rats.
By contrast the highest rate of cancers in the Uranium + Neutrons groups was 56%, and the lowest was 28%. Together with the high level of life-shortening in the Neutron-exposed rats, these results suggest that the Uranium particle effect was being swamped by some quite drastic effect from the Neutron dose acting on the immune systems of these poor animals.

The results for the "Uranium only" animals suggests that the particles were causing significant harm. This is borne out by the conclusions of the study itself:

... there could be reasons why the fission fragments [i.e. from Neutron bombardment] might not have been as effective as the alpha rays [from the Uranium particles] in causing malignant tumours of the lung.
What more do we need to say? Even in this study, which was not designed to examine the effects of Uranium particles, the particles alone were considerably more likely to cause cancers than the particles plus Neutron bombardment, or the particles administered after the Neutron bombardment.
More seriously, NRPB staff are presenting this study as a source of information on the human health effects of inhaling particles from incineration of contaminated waste, or any other source of alpha-emitting particles (e.g DU weapons). It is not, and NRPB's rôle in this is very worrying.


1 Further experiments to study whether localised fission fragment irradiation of rat lung causes tumours: Batchelor A T, Jenner T J, Cobb L M. Physics in Medicine and Biology 1983 Vol. 28 No. 5 475-483
NRPB's Dr. Edwards also cited Batchelor A T, Buckley P, Jenner T J, Major I R, Bailey M R, 1980 Int J. Radiat. Biol 37 249 - another neutron bombardment experiment.

Group exposure % life span (Controls = 100%) % rats with primary neoplasia of lung (Note a)
Uranium + Neutrons Groups I + II High U. dose 84% 58%
Uranium + Neutrons Groups I + II Low U. dose 83% 36%
Neutrons before Uranium Group III High U. dose 79% 41%
Neutrons before Uranium Group III Low U. dose 80% 33%
Uranium + Neutrons Groups I + II +III High U. dose 82% 56%
Uranium + Neutrons Groups I + II +III Low U. dose 82% 28%
Uranium inhalation only - High U. dose 93% 67%
Uranium inhalation only - Low U. dose 95% 10%
Unexposed controls - Group V 100% 2.6%

Table: Some results from "Further experiments to study whether localised fission fragment irradiation of rat lung causes tumours": Batchelor A T, Jenner T J, Cobb L M. Physics in Medicine and Biology 1983 Vol. 28 No. 5 475-483
(a) the third column shows only the number of rats with a specific diagnosis; the study does not present data for the numbers of cancers found.

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