RESEARCH Fallout Risk Evaluated AEC Commissioner Libby says t h e public's Sr e r a n c e will not be e x c e e d e d b y a t o m i c tests JLVADIOACTIVE FALLOUT is a
definite
risk, says Atomic Energy Commissioner Willard F . Libby. But, he adds, t h e risk should b e taken in context with life. It must be related to the chance we are willing t o take for progress. Libby poses t h e question: Should w e forego developing defenses that will save our lives because of this risk? The recommended tolerance for stiOntium-90—0.1 microcurie per individual—is still 200 times the level of Sr 90 in new bone in the U. S., says Libby. I t will n o t b e exceeded by fallout from weapons tests, he says, in any foreseeable circumstances. The Sr so tolerance set for the general public is 100 micromicrocuries p e r gram of b o d y calcium or what Libby calls 10O sunshine units (named for Project Sunshine, a world-wide study group working with the United Nations Scientific Committee on Effects of Atomic Radiation ) . Currently we have in our bodies 0.1 or 0.2 sunshine unit, says Libby. Children have about 0.5 unit. In pinpointing t h e hazards of fallout for the Washington Meeting of t h e American Physical Society, Libby said the Sr90 now in the stratosphere will fall out a t a rate about equal to t h e decay of material already deposited. On this basis, he sees no additional increase in Sr 90 from weapons fired in the past. If testing continues at t h e rate of t h e past five years, he says 4 to 15 sunshine units of Sr 90 will accumulate in human bones during t h e next 50 years. • Sr90 in Human Bone. Latest data on adult Sr 90 body burden are taken from examinations of bone removed during surgery (C&EN, Feb. 25, p a g e 30). But, fortunately, says Libby, actual data for the Sr 90 content of the entire bodies o>f several dozen stillborn children were collected in Chicago during 1953. T h e results of this study definitely establish t h e effect of previous fallout o n n e w bone. Because most adult bone was deposited before Sr*0 was produced, Libby says its Sr 90 content will not exceed t h a t for whole bone in infants whose total bodies are composed of t h e 38
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mixture of Sr 90 and calcium now present in food. Project Sunshine expects to continue this series and also to check adult bone data by analysis of complete skeletons. • Sr 9 ° a n d Calcium in Soils. Calcium i n topsoil is closely related t o the amount of Sr 9 0 deposited in human bone as a result of atomic weapons tests, says Libby. Though n o t proved conclusively, high available calcium seems to reduce the probability of Sr90 being taken u p in plants. B u t t h e effect does n o t hold for uptake directly by leaves. Sheep, goats, a n d cattle feeding on low calcium pastureland, Libby says, d o display a higher Sr90 content in bone. Work relating the calcium effect to Sr 90 uptake by humans shows t h e increase in Sr 9 0 in food due t o low calcium soils can hardly be more than fivefold for a fiftyfold deficiency. Where normal soil carries about 20 grams of available calcium in the top 2.5 inches, Libby says a region with only 0.4 gram would produce a human body burden five times greater than t h a t built up from foods grown in the normal soil. F e w individuals, however, accumulate Sr 90 in terms of the available calcium of t h e soil in their region, says Libby. Most people drink milk and eat cheese a n d other calcium-containing foods, and these reduce t h e effect of the calcium deficiency. T h e deficiency is also easily corrected by additions of calcium compounds to t h e soil. • Variations with Locality. Another cause of variation in Sr 9 0 content of humans with locality is t h e amount of fallout in given areas. In the U. S., with higher fallout because of t h e Nevada test site, the northern states have 20 to 30 millicuries of Sr 90 p e r square mile. In t h e South, the accumulation is somewhat lower. For average soil areas, these values produce a body burden between 1.7 and 3.9 sunshine units, says Libby. He says h e believes the new data on infants indicate t h e lower value is more realistic. Among people living in the same locality, L i b b y figures only one person in 3 0 0 wiil have more t h a n twice t h e average Sr 90 burden. T h e chances of anyone having as m u c h as three
times t h e normal burden, h e says, will be one in several million. In evaluating t h e effect of altitude, Libby compares Sr 90 exposure t o cosmic ray exposure because the physiological effects will be the same for the same energy absorbed. H e says one sunshine unit equals 3 milliroentgens a year. At this rate t h e difference between sea level and a n altitude of 5000 feet is about 8 sunshine units. Citing data gathered for 1947 on the occurrence of leukemia a n d bone cancer in Denver, New Orleans, and San Francisco, Libby says die figures show that other factors a r e more significant than cosmic ray dosage. However, h e says, they do confirm that t h e effect of altitude ( 8 sunshine units) will n o t cause a detectable increase in bone cancer and leukemia. Other effects of radiation on health, says Libby, require dosages of 25 to 50 roentgen units before they show u p as changes in t h e blood. Injury symptoms are n o t observed with less than 100 to 200 roentgen exposure. Libby says t h e dosages from test fallout are 100,000-fold smaller than these.
Caution on Cancer Cause Tobacco Industry Research Committee questions conclusions of Study Group on Smoking and Health S C I E N T I S T S SHOULD be as cautious in
accepting a claim that a cause has been found for cancer as they have been in accepting a claim of a cure for cancer. This is the thesis of the Scientific Advisory Board to the Tobacco Industry Research Committee in reviewing t h e opinion of the Study Group o n Smoking a n d Health (C&EN, April 8, page 27). T h e Study Group, organized at the suggestion of the American -Cancer Society, t h e American Heart Association, the National Cancer Institute, and the National Heart Institute, h a s said, "The sum total of scientific evidence establishes beyond reasonable doubt that cigarette smoking is a causative factor in t h e rapidly increasing incidence of h u m a n epidermoid carcinoma of t h e lung." Now t h e Tobacco Industry Research Committee's Scientific Advisory Board challenges that statement. It says that the status of research into lung cancer involves differences in beliefs about causes, one of which the Study Group has expressed. T h e TIRC board says it questions t h e existence of sufficient definitive evidence t o establish a simple cause and effect explanation of the complex problems of lung cancer. It
