Document kX73xnO5gV09OBo5nVw07XbJ

842 NATURE Au g u s t 20, i 966 using both the graphite rod and Tesla discharge techniques, were unsuccessful. Although no direct measurements of the power supplied to tho plasma by each generator have yet been made, approximate values were obtained by a load substitution method: tho power dissipated in a dummy load, a graphite cylinder of the dimensions required to produce the same load conditions as tho plasma itself, was determined by measuring tho equilibrium temperature of the graphite load in a slow stream of nitrogen and assuming that the power supplied was equal to tho rate of loss of heat by radiation (convection losses are comparatively small). This method has been shown by Reed' to give results which agree well with those obtained by using tho con ventional water-cooled calorimeter. The output from generator No. 2 was about 13 kW with generator No. 1 on (Tig. 2) and 10 kW with gonorator No. 1 switched off. Similar measurements on generator No. 1 indicated an output power of approximately 7 kW. There appears to be no reason why still lower frequencies should not be used provided that: (a) suitable means of initiation are incorporated, either by the use of a high- frequency pilot plasma as in the present work or possibly by pressure reduction as apparently used by Dymsliits; <f>) the size of the plasma torch is increased. We acknowledge tho assistance of E. Wilkinson (photo graphs), JT. G. Brett (construction of quartz and glass apparatus) and C. Tee (electronics). I. J. Fl o y d Alien Clark Research Centre, J. C. Le w is The Plessoy Co., Ltd., Caswell, Towoestcr, Northants. R. K. Ba y l is s Division of Molecular Science, National Physical Laboratory, Tcddington, Middlesex. > Babat, G. I., 3. Inst. Eke. Eng., 04, Ft. Ill, 37 (1947). * Reed, T. E,, 3. App. Phut., 32, 82) (1001). 8 Raboux, J., CJl. Acad. Sci., Paris, 2539 (1002). * Mlroner, A., and Hushfar, F., Amor. Inst. Aeronaut, and Astronaut. Electric Propulsion Conference, Colorado Springs, March 1963. 8 Marynowskt, C. V,'., and Mumne, A. G., Intern. Union Pure and App. Chein. Strmp. "Hiah Temperature Technology" Standard, California, 1963, 67-84 (1964). .Read, T. B,, Intern. Sci. Technol., No. 6,42 (June 1062). 2 Wilkinson, W. D., Radyne Ltd. (personal communication). Dymshlts, B. M., and Xoretskii, Ya. V., Soviet Phils.--Tech. Phys.,9,1294 (1965). Reed, T. B., Rev. Sci. Instrum.. 36, 620 (1065). RADIOBIOLQGY Measurement of Polonium-210 in Human Blood Po l o n io m-210 is a naturally occurring alpha-emitting isotope of the uranium series derived from decay of its long-lived parent, lead-210. Polonium-210 is present in most plants and foodstuffs, as well as in human tissues' Body burdens of this isotope arc usually determined by measuring its activity in tissue samples or urine2'5-5. Tissue samples other than teeth arc not readily available during life, however, and 24 h urine collections may bo difficult to obtain and process, yet are often necessary to quantify urinary excretion. Wo have found that potonium210 can bo easily deteotod in 10 ml. human blood samples by a simple radiochemical and counting technique. The measurement of polonium-210 concentration in blood may thus bo a practical method of estimating body burdons of this isotope, as well as of its parent lcsd-2102. As tobacco smoke has been shown to contain trace amounts of poionium-2106,'we have related blood concentrations to smoking habits in a group of middle-aged men. Ten ml. samples of fresh clotted blood wore weighed and digested in 30 ml. of hot concentrated hydrochloric acid, placed in plating cells with 0-5 N hydrochloric acid and SMOKERS SMOKERS Fiy, 2. Polonium-210 concentrations measured In 10 ml. blood samples from 100 healthy men 45-54 years of age 50 mg ascorbic aeid, and the polonium plated on to silver planchcts5'1. The planchets were counted for 48-72 li in low background gas-flow proportional counters2. Polo nium-210 concentrations as low as 0-3 pc./kg blood could be reliably measured by this method. Blood samples were obtained from 100 healthy men between the ages of 45 and 54 years, all of whom resided in one suburb of Boston. Detailed smoking histories were obtained from those men, and they were divided into tom- groups: current cigarette smokers, current pipe and/or cigar smokers only, past cigarette smokers (had been regular smokers until a year or more previously), and individuals who had never smoked. The results are presented in Tig. 1. Tho average polonium-210 concentration in smokers was 1-72 pc./leg blood, compared with 0'76 pe./ltg in non-smokers. Al though. a significant difference existed between blood concentrations in cigarette smokers and non-smokers (T < 0-001), a two to three-fold variation among individuals was present in each group. Such variation has also been observed among polonium-210 concentrations in pul monary tissues of different individuals2. In addition, we have examined other body tissues including liver, spleen, kidney, urinary bladder and bone obtained at autopsy from ten cigarette smokers and four non-smokers. Average concentrations were very similar to those re cently reported by Hill1, but up to a three-fold variation in concentrations in each organ was observed among individuals. The variation in blood concentrations may in part result from diotary factors. As Hill has pointed out, polonium-210 concentrations differ widely in various foodstuffs; beef and lamb kidney and certain shell fish, for example, may contain relatively large amounts of the isotope1. In a preliminary study of possible dietary effects, several blood samplos were drawn from an 85 kg subject before and after a meal containing about 100 pc. of polonium-210 (200 g of beef kidney). Blood polonium-210 concentrations were 0-S8 pc./kg before the meal and rose to a maximum of 1-56 pc./kg 12 h after the meal, which suggests that a significant fraction of the isotope present in food is absorbed into the blood. In separate experiments in four heavy cigarette smokers, blood samples were obtained before and at regular inter vals after sudden complete cessation of smoking. Blood polonium.210 concentrations fell an average of 27 per cent during tho first week after smoking was stopped, but thereafter changed very little during the next -1 8 weeks. N36935 DUP050312944 n o . 5051 Au g u s t 20. 1966 NATURE S43 111 addition to the polonium-210 normally inhaled and ingested by the general population, it has been estimated that cigarette smokers retain an excess of about 1-5 pc./day per twenty cigarettes, much of which may be cleared from, the lungs in the mucous sheet and swnllowcd'-3. The present results indicate that such small differences in chronic environmentalexposure to polonium210 can be detected in 10-ml. blood samples from exposed individuals. The values reported here should serve as a basolino to evaluate concentrations found in blood of individuals possibly exposed to high environmental levels of polonium-210 or its paront isotopes. In preliminary experiments, detectable concentrations of radium wore found in 10-ml. blood samples from two normal individuals. Analysis of small blood samples, therefore, may also prove useful in estimating body burdens of alpha-emitting iso topes other than polonium-210. We thank Dr. Edward P. Radford, jun., of the Univer sity of Cincinnati College of Medicine for confirming our counts on several of these samples in his laboratory. This work was supported by a grant from the Bureau of State Services, U.S. Public Health Service, and by a grant from the Rockefeller Foundation. J. B. Lit t l e R. B. Mc Ga n d y Departments of Physiology and Nutrition, Harvard School of Public Health, Boston, Massachusetts. ' 1 Hill, 0. It., Nature, 80S, 42S (106S). A.......... ' ITolteman, R. B,, Eeallh P/j v a., 9,335 (1903). * Little, J. B., a al,, Radial. Rea.. 23. 209 (1984). * Radford, jun., E. P., Hunt, V. R,, and Sherry, D.. Jtntfwi. fur;., 19, 298 (1963). 1 Jackson, S., and Dolphin, G. W, Health Plujs., 12, 481 <1066). * Radford, jun., E. P,, and Hunt, V. R., Sconce, 143, 247 (1964). : Little, J; B., Radford, jun., 35. P., McCombs, H. L., and Hunt, V. R., Xete Engl. J. Med., 273,1343 (1005). Caesium-137 in Edible Freshwater Fish Kn o w l ed g e of radioactivity in fish is largely limited to determinations made of the strontium-90 occurring in certain ocean species and to some attempts at the evalua tion of caesium-137 content (13TCs) of the same or similar specimens. Hasanen. and Miettinen' found concentrations of the order of nanocuries of caesium-137 per kilogram (lie./kg) in freshwater fish. Those were taken from lakes in Finland during 1962 and 1963 in the course of an investigation into sources of caesium-137 other than caribou and reindeer meat in tbo Laplander's diet. This finding could have boen predicted from the earlier work of Pendleton and Hanson3, which demonstrated the rapid accumulation of caesium-137 by various aquatic forms through several trophic levels in a freshwater pond contaminated with caesium-137. Caesium-137 in these organisms was found to reach concentrations several orders of magnitude greater than those found in the surrounding water. During the first 3 months of 1965, the concentrations of. caesium-137 present in freshwater fish available commer cially in. tho Chicago area v.-erc similar to those found a bier in Finland (Table 1). The fish (which were pur chased at random in local food markets) wero boned fillets (except for smelts) and ready to cook. Both the concentration of caesium-137 and of potassium-40 were '1' tomiined by gamma-ray spectrometry in 1-2-kg samples of fresh fish using conventional low-background tech niques. A number of varieties of ocean fish wore also "xnmined mul showed appreciably lower concentrations ('I eaosium-137 but similar potassium levels (Table 1). fhis inherent difference between salt and freshwater pi'oie.s as regards the content of cacsium-137 had been previously noted by Hasanen and Miettinen1. The caesium-137 concentration present in fish depends primarily on throe factors: (1) tho concentration of 'bis radionuclide in the water environment; (2) the accompanying lovel of potassium (ratio of cacsium-137: potassium); (3) the position of tho fish in question in tho aquatic food chain (that is, the trophic level). Published values of cacsium-137 in salt and freshwater arc sparse. However, monthly measurements in Lake Huron showed average concentrations of 0-4 and 0-3 pe./l. during 1963 and 1964, respectively3. During this same interval the concentration in lakes and rivers in the vicinity of Chalk River, Ontario (presumably uneontaminated By reactor wastes), was three to four times greater than tbat in Lake Huron3. Surface waters of the Pacific Ocean sampled in mid-1963 indicated an average level of 0*6 pecaesium-137/1. (ref. 4). Profiles of caosium-137 activity in. ocean water have shown decreasing concentration with depth3. Judging by the limited data available, there did not appear to be appreciable differences between the concentration of caesium-137 in salt and freshwater. Howpver, the possibility exists that closed lakes which do not possess large dilution capacity may contain higher levels of caesium-137 because they collect the run-off from large areas. Conversely, because of the large dilution effect possible in the oceans, the effective concentrations may be much lower than that observed in surface watas. The potassium content of the oceans is ten to several hundred times greater than of freshwater. The value in the oceans, based on a large number of analyses, is fairly constant, and is given as 380 parts per million (p.p.m-)*The few measurements taken in tho Great Lakes show values of a few p.p.m., with smaller lakes and rivers in the area containing somewhat higher amounts'. Amounts in closed lakes in this region and further north are an order of magnitude higher, with values approaching . marino concentration in some instances'. Tho concentra tions of rubidium and stable caesium are several orders lower than that of potassium in both salt and freshwater and are almost insignificant31'. The greater concentration of caesium-137 in freshwater fish, seen in Table 1, probably reflects, in the first platoe, . the higher caesium-137 : potassium ratio present in fresh- . water*. The trophic level is also a factor--as shown by tho higher caesium-137 concentration in carnivorous fish as . opposed to plankton feeders and other non-carnivorcras fish, in both salt and freshwater. The lower concentra tions in lako perch and smelt may also result from younger age at capture as well as different feeding habits. The question now arises as to what effect the presence of relatively high concentrations of caesium-137 in fresh water fish may have on the average intake by human beings Table 1. Ca e s iu m-1S7 ADD Po t a s s u m ix Sa l t a x d FREsnwATF.it Fisa PURCHASED BETWEES JASUAKV AMI APRIL 1965 Species* Cs Potassium Feeding habits (pc./kg (MfltE , wot weight) wet weight) la,Cs po.M*C Freshwater fish .Lake trout " Pibe Whitcflsh Lake perch Smelts Carnivorous t Plankton }t 2,210 8,874 2,923 2,610 1,428 1,167 1,816 328 265 365 330 327 377 2-49 3-50 2-90 3-58 3-25 2*47 3*57 3*51 3*65 2-89 2-96 2-GO 3-17 887 1,107 1,008 729 439 472 369 93 73 126 111 120 119 ' Marino fish Flounder Halibut Ocean perch Ocean catfish Haddock Salmon Cod Red snapper Bottom feeder, molluscs, etc. Carnivorous "Plankton, annelids Carnivorous ,, 24 02 32 50 43 60 71 43 12 2*88 5*26 3*08 3-11 404 4*02 3*51 4*17 1-76 8-3 11*8 10*418-9 10-0 16*4 20-2 10*3 6-8 * The common or commercial names of ftBh are used here Instead of taxoiaoralc names because of tbo difficulty In determining the latter with any precision with fror.cn, dressed fish. f `{' aniivcirous' Is meant to Imply feeding on fish and other animals smaller than the llsh in ipicstion. 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