. ‘\ (7% =f > Health Physics Pergamon Press 1973. Vol. 24 (May), pp. 555-557. Printed in Northern Ireland Fallout “’Cs Levels in Man Over a 12 yr Period* (Received 7 July 1972; in revised form 3 August 1972) AFTER the partial test ban treaty in 1963 and subsequent stopping of nuclear weaponstesting in the atmosphere by United States and Soviet Union, the level of radioactive contamination in the biosphere Ten normal and healthy subjects (7 males and three females) who were counted once every month for 12 yr are employees of Brookhaven National Laboratory (BNL). These subjects did not have any significant occupational contact with radioactive substances. At the start of study their age ranged from 25 to 45 yr. In addition to #7Cs measurements, body potassium of these subjects was also measured by counting has been reduced considerably, China and France gamma ray activity of naturally occurring radiowhodid not sign this treaty, continue weaponstesting isotope K, in the atmosphere. At the present time there is no significant increase in the levels of radioactive conResults and Discussion tamination from these latter tests, as these constitute a Because 137Cs follows a metabolic path similar to very small per cent of total tests conducted by the _ that of potassium andis found mainly in muscle mass, U.S.A. and U.S.S.R. Nevertheless, these tests do pose body burdens of 13’Cs. are expressed in terms of body possible future hazards and should testing continue, potassium (pCi/g). This ratio tends to minimize the periodic monitoring of the atmosphere and human spread in values due to variations in body weight. subjects is necessary. The results are presented in Fig. 1. After nuclear Cesium-137 is one of the products which results weapons testing in the atmosphere was stopped from nuclear explosions. Because ofits long halflife towards the end of 1959, there was a drop in the (Ty = 30 yr) and ease with which it enters into the specific activity of 487Cs, and the average valuein 1961 body through food and milk, ®’Cs presents a potential was 37 pCi/g. Anperson™) of Los Alamos Scientific radiation hazard to man. This report presents body burdens of ’?Cs observed in a selected population of Laboratory (LASL) reported 25-30 pCi/g at the end Long Island from the beginning of 1960 until the end of 1961. Cesium-137 levels in man started rising in been previously reported, Methods and Materials _was about 75 pCi/g and in March 1963 it rose to 110 pCi/g.4) In the present study, the average value for 1963 was 80 pCi/g which reached a maximum value of 180 pCi/g in August 1964. The sharp rise was ob- Cesium-137 emits a gamma ray of energy of 0.66 MeV and body burdens of cesium can be measured with whoie body counter. Two different Brookhaven whole body counters were used for the measurements. Initially, an 8 x 4-in. sodium iodide served during the spring of the year associated with more sensitive and advanced 54 crystal detector 18-20 pCi/g with very little change in level in 1970 and 1971. crystal detector was used in a standard chair counting geometry.'2) In 1967 this system was replaced by a system with an on-line computer facility.4) This system, in addition to its high sensitivity, corrects individually for body absorption of gamma rays employing broad-beam !57Cs sources and a computer program.'3) The counting time was reduced from 30 min in chair geometry to 15 min in 54 crystal geometry. As usual, to avoid any possible external contamination, each subject changes to hospital dress and showers prior to counting. Both the systems were intercalibrated before the switch over. * Research supported by the U.S, Atomic Energy Commission. Repository 5a1Zb29 1962 again after the start of a new series of tests in 1961. In December 1962, specific activity of 7Cs SVL heavy rainfall. The 18’Cs levels were lower in female by 20°% when compared with males. After the test ban treaty in 1963 and subsequent decrease in radioactive contamination in atmosphere, 137Cs concentration in manstarted declining towards the end of 1964. The average value for 1969 was A comparison of the present results with those of other investigators is shown in Fig. 2, The numberof variables involved in the level of ’Cs make it difficult to compare the results from other countries. Some of these variables are food habit, geographical location and the variability of biological half life of The rate of fall of the ®’Cs concentration in human beings was found to have a half life of about 520 days from September 1964 until 1968. RECORDS ISLANDS BOxNo LEDICAL DEPT PYBLICATIONS —#F/3 79 ~ 144] i well with LASL, however, the corresponding valuesin the U.S.S.R. were uniformly higher (Fig. 2). cottection MARSHALL Fotoen : 187Cs in man. Results obtained by BNL compare very The Medicu) Reosen rehy Center Brookhaven Natio pid Lecerato Upton, L. L, New Yo rk © ry ee le PE, ee ie ete me on of 1971. Estimates of total radiation dose are also given and the results are compared with those of other investigators. Early results of this investigation have