§ Mr. Masonasked the Prime Minister (1) what estimate he has received from the Medical Research Council as to how many years must elapse, at the present rate of atom and hydrogen bomb testing by the three nations concerned, before the strontium 90 fall-out reaches warning level of 10 units; and what proposals are now before the Council, with a view to lowering this level so as to err more on the side of human health and safety;
(2) what estimate he has received from the Medical Research Council as to how long, on the assumption that there will be no more atom and hydrogen bomb tests, the stratospheric reservoir of strontium 90 will take to disappear at the present rate of fall-out, and the extent to which it is likely, by its accumulative effect, ever to reach the warning limit of 10 units prescribed by that body.
§ Mr. R. A. ButlerI have been asked to reply.
Some forecasts on the rate and duration of fall-out from past and future weapon tests are given in the report of the Atomic Energy Research Establishment, Harwell, entitled "The World Wide Deposition of Long Lived Fission Products from Nuclear Test Explosions", a copy of which is in the Library.
A close watch is being kept on the strontium content of human bones in the United Kingdom. The relationship between the forecasted fall-out of radio-strontium and the future trend of its concentration in human bones is very complex, but I am advised that the present trend of evidence is consistent with the view expressed in paragraph 282 of the 220W Medical Research Council's report on "The Hazards to Man of Nuclear and Allied Radiations", that a level of 10 units in human bone might be reached in this country in the course of several decades if nuclear tests continued.
The figure of 10 strontium units, suggested by the Medical Research Council as the level of concentration in the bones of the population, at some point beyond which the matter would require serious consideration, is well below the internationally accepted occupational level of 1,000 units and the concentration of 100 units which the Council recommended should be the maximum allowable for the general population.