§ Mr. Newensasked the Minister of Agriculture, Fisheries and Food what is the quantity of strontium 90 present in milk, soil and the bones of sheep at intervals of five years from 1945 until the present.
§ Mr. StrangSampling of food and the environment was begun in the middle 1950s by the Atomic Energy Authority and by the Agricultural Research Council when it became apparent that demonstrable amounts of radio nuclides were being deposited in the United Kingdom from world-wide fall-out. Spot samples of dried milk taken in the period 1955–57 indicated a Sr-90 content of 3–4 pCi/g Calcium. Subsequently the country wide survey begun in 1958 by ARC showed the following mean concentration in milk: (pci Sr-90/g Calcium) 1958 (7.0); 1963 (25.6); 1968 (7.6); 1973 (4:1).
Estimates for soil content are based on measurements of radio nuclides in rain made by AEA and are given in the form of cumulative deposits corrected for radio-active decay (mCi Sr-90/km2): 1958 (15); 1963 (53); 1968 (71); 1973 (67).
Measurements of Sr-90 content of sheep's bone are not routinely made as these do not relate to human diet, nor are they closely related to fall-out measurements in pasture. There is, however, no risk of injury to sheep judging by the few measurements for which results are available.
§ Mr. Newensasked the Minister of Agriculture, Fisheries and Food what estimate he has made of the presence of the long-lived radioactive by-products of H-bomb tests apart from strontium 90, such as radio strontium, radio caesium and caesium 137, in the atmosphere and the soil in the United Kingdom at intervals of five years from 1945 until the present, together with the average level of absorption of these substances by 597W members of the population of different ages.
§ Mr. StrangCa-137 is the only radioisotope in fall-out radiocaesium. Radio strontium consists of Sr-89 and Sr.90.
Amounts of caesium-137 deposited in rain are closely related to those of Sr-90 and build-up in soil is also similar. Milk and meat are the principal sources of Cs-137 in diet in the United Kingdom and, as the concentrations in the two foods vary in a similar manner when they are produced in the same area, measurements on milk indicate the trends in levels of dietary contamination. Mean concentrations of Cs-137 in the United Kingdom have been (pCi Cs-137 per litre milk): 1961 (21); 1965 (98); 1970 (17); 1973 (8).
Limiting levels of radiation dose at which action would have to be considered are laid down for the United Kingdom by the Medical Research Council based on recommendations of the International Committee for Radiological Protection. The derived working limit for Cs-137 in milk has been calculated from these figures by the National Radiological Protection Board as 30,000 pCi Cs-137 per litre.