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In 1976 the annual rate of deposition of 90Sr from atmospheric tests of nuclear weapons reached its lowest value since the systematic measurement of radioactive fallout began in the 1950's. The late 1976 Chinese tests may have contributed about 9 kCi to the total of about 49 kCi deposited during 1976.The past few years have seen a renewed public and scientific interest in the fallout of the radioactive debris produced by atmospheric tests of nuclear weapons. This interest has mainly concerned environmental levels of the fission product, 131I, which has an 8.04-day half-life. This nuclide was studied less intensely during the early years of fallout measurements, however, than was the long-lived fission product, 90Sr, which has a half-life of 28.6 years. Consequently, there is some merit in considering the more complete historical record of deposition of 90Sr in evaluating the relative significance of the contribution by recent nuclear weapons tests to levels of environmental radioactivity.The Environmental Measurements Laboratory (EML), which prior to October 1977 was named the Health and Safety Laboratory (HASL), has maintained a worldwide network of samplers since 1957 to collect fallout to be measured for 90Sr.Based upon data from this network, an estimate has been made each year (1) since 1958 of the annual worldwide deposition and of the cumulative deposit of 90Sr. The EML network of samplers of 90Sr fallout grew during 1957-1964, and included 142 sites in 1964, 99 in the Northern and 43 in the Southern Hemisphere. During 1964-1975 the network gradually decreased in size, and in mid-1976 it was cut back to 72 sites, 47 in the Northern and 25 in the Southern Hemisphere. The samples are collected at these sites by exposing either a steep-walled, stainless steel pot or a plastic funnel which drains through a column containing Dowex-50 ionexchange resin. At the end of each month, the total material collected in each pot and each exposed column of ion-exchange resin is analyzed radiochemically for 90Sr. Starting with the July 1976 sample, analyses have been made on quarterly composites. The analyses are performed at contractor laboratories using procedures similar to those used at EML (2). ResultsAll of the detailed monthly precipitation and radiochemical data accumulated since the inception of the EML pot and column network have recently been tabulated (3).Various methods for calculating the total fallout of 90Sr on the surface of the earth from limited data were discussed by Volchok (4). Some of these methods involve the analysis of soil samples, while others involve the analysis of precipitation samples. In some of these methods, the values of 90Sr per unit area of the surface of the earth are averaged over each latitude band, while in others the concentrations of 90Sr per unit volume of rainfall are averaged over each latitude band and this average is multiplied by an assumed value of average annual
Leeds1 Although, long half-life compounds appear to be more appropriate pharmacological indicators of compliance with treatment, short half-life markers or measurements of short half-life therapeutic drugs are frequently used. 2 We have compared the usefulness of low-dose phenobarbitone (a long half-life indicator), low dose isoniazid (a short half-life marker) and controlled release metoprolol (Metros) (a controlled release formulation of a short half-life 'therapeutic' drug) in seven volunteers with simulated partial (two thirds) compliance. 3 Detection of isoniazid metabolites in urine had an 83% sensitivity and 94% specificity for detecting ingestion within the previous 24 h and 100% sensitivity and 82% specificity for detecting ingestion within the past 6 h but gave no indication of the longer term pattern of compliance. 4 At 28 days (a time when steady-state would be obtained for all three drugs) phenobarbitone plasma levels were 70% (66-76%)-median and interquartile range-of the expected steady-state level if compliance had been complete. Corresponding figures for metoprolol were 82% (37-100%). 5 Measurement of phenobarbitone was much superior to isoniazid or metoprolol measurements in reflecting partial compliance over the previous 1 to 4 weeks.
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