? > \ i 7% =f) Health Phystes Pergamon Press 1973. Vol. 24 (May), pp. 555-557. Printed in Northern Ireland 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 has been reduced considerably. China and France whodid not signthis treaty, continue weaponstesting in the atmosphere. At the present time there is no significant increase in the levels of radioactive contamination from theselatter tests, as these constitute a very small per cent of total tests conducted by the U.S.A. and U.S.S.R. Nevertheless, these tests do pose possible future hazards and should testing continue, periodic monitoring of the atmosphere and human subjects is necessary. Cesium-137 is one of the products which results from nuclear explosions. Because ofits long half life (Ty = 30 yr) and ease with which it enters into the body through food and milk, 137Cs presents a potential radiation hazard to man. This report presents body burdens of !37Cs observed in a selected population of Long Island from the beginning of 1960 until the end 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 been previously reported.) Methods and Materials Cesium-137 emits a gamma ray of energy of 0.66 MeV and body burdens of cesium can be measured with whole body counter. Twodifferent Brookhaven whole body counters were used for the measurements. Initially, an 8 x 4-in. sodium iodide crystal detector was used in a standard chair counting geometry.'2) In 1967 this system was replaced by a more sensitive and advanced 54 crystal detector system with an on-line computer facility.) This system, in addition to its high sensitivity, corrects individually for body absorption of gamma rays employing broad-beam 47Cs sources and a computer program.” 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. Rerositony SVL 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 87Cs measurements, body potassium of these subjects was also measured by counting gamma ray activity of naturally occurring radio- isotope “K, Results and Discussion Because 387Cs follows a metabolic path similar to that of potassium and is found mainly in muscle mass, body burdens of 157Cs are expressed in terms of body potassium (pCi/g). This ratio tends to minimize the spread in values due to variations in body weight, The results are presented in Fig. 1. After nuclear weapons testing in the atmosphere was stopped towards the end of 1959, there was a drop in the specific activity of 87Cs, and the average value in 1961 was 37 pCi/g. ANpERson4) of Los Alamos Scientific Laboratory (LASL) reported 25-30 pCi/g at the end of 1961. Cesium-137 levels in man started rising in 1962 again after the start of a new series of tests in 1961. In December 1962, specific activity of 87Cs _ was about 75 pCi/g andin March 1963 it rose to 110 pCi/g.) 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 observed during the spring of the year associated with 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 man started declining towards the end of 1964. The average value for 1969 was 18-20 pCi/g with very little change in level in 1970 and 197]. A comparison of the present results with those of other investigators is shown in Fig, 2. The number of variables involved in the level of 487Cs make it difficult to compare the results from other countries. Someof these variables are food habit, geographical location and the variability of biological half life of 137Cs in man. Results obtained by BNL comparevery well with LASL, however, the corresponding valuesin the U.S.S.R. were uniformly higher (Fig. 2). 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 conection SIARSHALL ISLANDS BOxNo LEDICAL DEPT PUBLICATIONS Fotoem —fF/379 - 144) The Medics) Resene ch Center Brookhaven Nattons] Levuralory Upton, L, {,, New Yo rk ‘ { NB ee ta ae oe Fallout ’Cs-Levels in Man Over a 12 yr