issible nuous ordine issivnle r sugconre, so ld be served 7aters. a than om has Inited 1uman tivity ild be de by mean t least wn to 30 the in the wuman many reting ations daily me to tivity From the latest figures available (for the first half of 1959) we calculate the mean contents of strontium90 and cesium-137 in surface waters as 0-75 uyuc./litre and 0-20 uue./litre, respectively. The mean daily intakes of populations ingesting such drinking waters would therefore be 1-9 uuc. and 0-5 unc. of the two nuclides, respectively. For large populations the International Commission on Radiological Protection suggests 33 uyuc./litre and 6,000 yye./litre in water, respectively, for these materials as the maximum permissible concentrations. It will be seen that the observed values are very small in comparison to these permissible levels. Note added in proof. Since these investigations were completed, we have had the opportunity of examining specimens of drinking waters supplied to Horrabridge, Devon. The radioactivity of these particular waters has been the subject of recent communications®*.23 concerning the incidence of cancer in the area. We find the long-lived natural activity of the Sampford Spiney supply to be 0:6 puc./litre, and its content of radon + daughters 2,500—5,000 uuc./litre. It will be seen that these values are well within the range reported in Table 1 above for waters in south-west England. Many of the water samples were obtained through the goodwill and co-operation of Mr. A. W. Kenny, of the Ministry of Housing and Local Government, who kindly approached on our behalf the chief engineers of numerous water undertakings, to all of whom we would like to express our sincere thanks. Our thanks are also due to Mr. J. Crookall, of this Department, for chemical estimations carried out on a number of the samples. 1 Turner, RB. C., Radley, J. M., and Mayneord, W. V., Health Phys., 1, 263 (1958). * Stehney, A. F., deta Radiol., 43, 43 (1955). * Hursh, J. B., and Gates, A. A., Univ. Rochester Rep. OR, 257 (1953). 4 Lucas, H. F.. and Itcewiez, F. H., J. Amer. Waterworks Assoc., 50, 1523 (1958}. * Krause, D. P., A.N.L. Rep. 5967 (Dec, 1958). * Lucas, H. F., and Krause, D. P., Radiology, 74, 114 (1960). 7 Rajewsky, B., Muth, H., Hantke, H. J., and Aurand, K., Strahlentherapre, 104, 157 (1957). 4 Jacobi, R. B., J, Chem. Soc., 3, 314 (1949). * Thomson, J. J., Phil. Mag., 4, 352 (1902). Turner, R, C., Radley, J. M., and Mayneord, W. V., Brit. J. Radiol., $1, 397 (1958). 1 Rosholt, J. N., Anal, Chem., 29, 1398 (1957). ‘1 Mayneord, W. V., Turner, R. C., and Radley, J. M., Vature, 187, 208 (1960). ta Smith. H., and Chandler, T. BR. D., United Nations Conf., P/298 4 Rona, E., and Urry, W. D., Amer. J. Set,, 250, 241 (1952). 15 Scott, R. C., and Barker, F. B., United Nations Conf., P/778 (1958). 16 Recommendations of the International Commission on Radiological Protection, rit, J. Radioel., Supp. No. 6 (1955). "7 Meyer, 5., Mitt. Des Instituts far Radium Forschung, No. 238, Wien (1929), 18 International Commission on Radiological Protection, Report of Committee IL (Pergamon Press, London, 1959). '® Marineili, L, D., dimer. J. Roentgenol,, 90, 729 (1958). 20 Mayneord, W. V., Radley, J. M., and Turner, R. C., Ade. Sei, No. 64, 363 (March 1060), 21 Crooks, R. N., Osmond, R. G. D., Owers, M. J., Fisher, E. M. B., and Evett, T. W., A.E.R.E.—R 3127, London (H.M,8.0., 1959). *? Allen-Price, E. D., Lancez, i, 1235 (1960). 33 Ane I)., Lakey, J. R. A., and Mathias, D. J., Lancet, ii, 1272 100 or icular re the ugher ntake range atural yution nking aving food ice of retain, 1 form nents, food, made zation actors e the ‘in daily on to tivity n-137 iduets iivity, irface itents values Printed in Great Britain by Fisher, Knight & Co.. Ltd., St. Albans,