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Nuclear explosion fallout - Biological effects - Report of meeting between Australian and French scientists, Canberra, 7-9 May 1973


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THE PARLIAMENT OF THE COMMONWEALTH OF AUSTRALIA 1973—Parliamentary Paper No. 29

BIOLOGICAL EFFECTS OF NUCLEAR EXPLOSION FALLOUT

REPORT OF MEETING BETWEEN

AUSTRALIAN AND FRENCH SCIENTISTS

CANBERRA

7 - 9 May 1973

Presented by Command

and ordered to be printed 17 May 1973

THE GOVERNM ENT PRIN TER OF AUSTRALIA CANBERRA: 1973

Printed by F. D. A t k in s o n , Government Printer of Australia

MEETING BETWEEN AUSTRALIAN AND FRENCH SCIENTISTS

7-9 MAY 1973

AT THE AUSTRALIAN ACADEMY OF SCIENCE, CANBERRA

PRESENT—

Australian side

Sir Rutherford Robertson

Professor S. T. Butler

Dr D. Metcalf

Professor M. J. D. White

Dr C. Η. B. Priestley (present for two sessions to discuss meteorological questions)

French side

M. le Professeur A. Gauvenet

Dr D. Mechali

M. J. M. La vie

M. A. P. Chaussard

REPORT OF THE AUSTRALIAN SCIENTISTS

SECTION A

This section is identical in the reports of both the Australian and French scientists

1. Dose commitments

There was general agreement that the technical methods used by the Australian authorities for measuring quantities of radiation fall-out are satisfactory and are in accordance with international practice. A large degree of agreement was reached regarding the levels of dose commitment in Australia due to past French tests. The estimates of those dose commitments in millirads are as follows (for strontium-90 and caesium-137, the lower figures are preferred by the French scientists according to their method of estimation; the Australian scientists’ estimates are the higher figures):

Thyroid

Element

Thyroid (young children)

(older children and adults)

Blood forming cells

Bone cells

Whole body

Iodine-131 . . . 97 9 0 0 0

Short lived . . . 1.5 1.5 1.5 1.5 1.5

Strontium-90 . . 0 0 4 .0 -6 .2 5 .6 -8 .5 0

Caesium-137 (external) . 2 .0 -3 .0 2 .0 -3 .0 2 .0 -3 .0 2 .0 -3 .0 2 .0 -3 .0

Caesium-137 (internal) . 0 .9 -1 .3 0 .9 -1 .3 0 .9 -1 .3 0 .9 -1 .3 0 .9 -1 .3

Carbon-14 . . . 0.2 0 .2 0 .2 0.3 0.2

Total (in round figures) . 102-103 14-15 9-12 10-15 5-6

The estimates of the dose commitments due to all tests are as follows (the figures were provided for the meeting by an Australian government scientist; the values for the French tests are the higher values from the preceding table):

Element

Thyroid (young children)

Thyroid (older children and adults)

Blood forming cells

Bone cells

Whole body

French tests . . . 103 15 12 15 6

Tests by other nations . 74 54 83 96 52

Total for all tests . . 177 69 95 111 58

Both delegations agree with the method which has been used to obtain these figures.

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2. Biological effects

There was general agreement between both groups that for certain dose levels, radiation is known to cause damage in humans. However, there may be a threshold below which lower levels of radiation have no effect, the action on human beings of low doses and very low doses such as result from the tests never having been observed.

Current work, for example on the phenomenon of repair by living cells of damage they have suffered at high doses of radiation, suggests that low doses may not cause cancer or genetic defects at a rate proportional to dose. Nevertheless the international authorities have prudently accepted the hypothesis of direct proportionality in order

to establish accepted dose limits. Certain additional factors may operate to reduce significantly the risks below those predicted from a simple estimation based on proportionality. These include the lesser effects of certain types of radiation, radiation received at low dose rates, or over extended rather than brief time periods.

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SECTION B

This section is the sole responsibility of the Australian scientists.

The Australian scientists stressed that, despite the uncertainties outlined in the above discussion of biological effects, the only prudent course in attempting to assess the overall risk to the Australian population was to assume direct proportionality of all biological effects to radiation dosage. This is the public health position taken by the United Nations Scientific Committee on the Effects of Atomic Radiation and by other recognised authorities. The Australian population is large enough that even very small linear estimates of risk, in the region of the radiation doses due to the French tests, yield finite estimates of deaths due to cancer and genetic abnormalities. The Australian scientists believe that it is necessary to accept such estimates as realistic and not to take into account notions of a hypothetical threshold dose below which damage would not occur. Assuming a linear relationship between dose received and using maximum published figures for radiation risks, it has been calculated that, as a result of past French atomic tests, a final total of 26 cases of thyroid cancer and

14 cases of leukaemia and other cancers could result in the Australian population. The Australian scientists present believe that, as a result of the French tests that have already occurred, there could be approximately one death or serious disability in Australia from genetic causes during the first generation and 18 deaths in all subsequent generations; these are minimum estimates, and maximum estimates based on present information (see the Report of the Advisory Committee on the biological effects of ionizing radiation, U.S. National Academy of Sciences, November 1972) would be approximately 15 times these figures.

The above figures are based on the dose commitment estimates from the French tests given in the tables in Section A. It should be noted that the report of the Academy of Science Committee estimated the steady radiation effects to Australia from French tests in the Pacific, assuming continued testing at the French site on a pattern similar to that of the past seven years, and the harm commitments given in the report must be interpreted in this light. The dose commitments for the seven years of French testing in the Pacific are included in the report. Together with the risk factors used in the report, these commitments permit a direct computation of the harm commit­ ments to the Australian population from the past tests.

The Australian scientists drew attention to the additional harmful effects which would accrue to the Australian population as a result of the improbable event in which the explosion of a high-powered bomb was combined with quite exceptional meteorological conditions giving a high fallout over Australia (Appendix—Academy Report).

Although the levels of radiation due to the French tests are unlikely to cause a statistically detectable increase in the frequency of cancer or genetic abnormalities in Australia, it is emphasised that there should be no unwarranted exposure to radiation. Further, with the long-lived isotopes produced as the result of nuclear explosions, the genetic effects on the Australian population, though small, are cumulative.

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REPORT OF THE FRENCH SCIENTISTS

SECTION A

This section is identical with Section A in the Australian report.

SECTION B

This section is the sole responsibility of the French scientists. *

1. Biological Interpretation

The risk calculated from observations made following high doses of radiation and without taking into account the various considerations described above therefore represents the upper limit of risk and not the actual risk. The actual risk may be considerably lower, it may be nil.

Moreover the French experts consider that the values for the upper limits put forward in the Australian documents are greatly overestimated for cancer (particularly for cancer of the thyroid) and leukaemia and that, even taking the hypothesis of a proportional relation without a threshold, it would nevertheless be necessary to take into account the fact that it is a question of radiation spread over a very long period

of time. So far as genetic effects are concerned the values put forward follow from those given in the latest report of the UN Scientific Committee on the effects of radiation. These values represent the upper limit of risk.

The significance of the annual dose commitments resulting from the tests can be better appreciated, and in a more simple manner, by comparing them on the one hand with natural radiation and with its regional and local variations, and on the other hand, with the annual doses limits recommended by the International Commission for Radiological Protection of members of the public based on the hypothesis of

permanent exposure.

The annual dose commitments resulting from the French tests and which, moreover, for the part which can be ascribed to long-lived products will be spread over many years, are about 15 millirads for the thyroid and of the order of 1 millirad or several millirads in all other cases. They are very much less than natural radiation

and its variations; in fact, on an average this is 100 millirads per year and frequently is more than double that figure; the local variations are noteworthy because they sometimes vary within the same city by 1 or several dozens of millirads and that could be the case in certain large Australian cities. The annual dose commitments

resulting from the tests are only about one thousandth to several thousandths of the limits of annual doses recommended by the International Commission for Radiological Protection of members of the public.

* This is the Australian translation of the French scientists’ report.

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2. Temporary unusual occurrences in the atmosphere

The two groups examined the problem posed by the existence of temporary unusual occurrences in the behaviour of the atmosphere which, as the Australian Academy of Science report indicates, could cause, for a given test, over a limited region, fall-out higher than that observed simultaneously in the surrounding areas.

For this effect to happen, the occurrence of these atmospheric peculiarities, which are moreover rare, must coincide with the simultaneous presence, in very exact locations, of radioactive cloud.

The French group presented the results of studies on experiments on this complex problem carried out in France; certain of these results have been published by the French Academy of Science.

The French experts judge that because of the relative geographic position of Australia and the test zone as well as the meteorological constraints imposed on those conducting the experiments, it is highly improbable, if not impossible, that this effect could lead to a noticeable increase in fall-out over the Australian continent.

Moreover, this phenomenon has not been observed in Australia during previous tests. As for the rare cases observed in the northern hemisphere, only a low increase (of the order of a few per cent) in dose commitments has resulted, because of the temporary and local character of the increase in radioactivity.

3. Conclusions

The level of dose commitments resulting from the French tests in the Pacific, their comparison on the one hand with the natural radiation levels to which man is permanently exposed and on the other hand with the dose limits established with the greatest prudence by competent international organisations, show that the fall-out as a result of these tests can in no way constitute a danger to the health of populations.

The French experts feel that on certain points, notably on the effects of unusual meteorological occurrences, further exchanges of views based on existing documenta­ tion, could enable a better appreciation of the respective positions of the two groups.

14257/73—(R72/2824)