RESEARCH

Fallout Risk Evaluated AEC Commissioner Libby says the public's Sr tol­e rance will not be exceeded by atomic tests

JLVADIOACTIVE FALLOUT is a definite risk, says Atomic Energy Commissioner Willard F . Libby. But, he adds, the risk should b e taken in context with life. It must be related to the chance we are willing to take for progress. Libby poses the question: Should we 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 Sr90 in new bone in the U. S., says Libby. I t will not be exceeded by fallout from weapons tests, he says, in any foreseeable circumstances.

The Srso tolerance set for the gen­eral public is 100 micromicrocuries per gram of body 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 the hazards of fallout for the Washington Meeting of the American Physical Society, Libby said the Sr90 now in the stratosphere will fall out a t a rate about equal to the decay of material already deposited. On this basis, he sees no additional in­crease in Sr90 from weapons fired in the past. If testing continues at the rate of the past five years, he says 4 to 15 sunshine units of Sr90 will ac­cumulate in human bones during the next 50 years.

• Sr90 in Human Bone. Latest data on adult Sr90 body burden are taken from examinations of bone removed during surgery (C&EN, Feb. 25, page 30 ) .

But, fortunately, says Libby, actual data for the Sr90 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 the effect of previous fallout on new bone.

Because most adult bone was de­posited before Sr*0 was produced, Libby says its Sr90 content will not exceed tha t for whole bone in infants whose total bodies are composed of the

mixture of Sr90 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.

• Sr9° and Calcium in Soils. Cal­cium in topsoil is closely related to the amount of Sr90 deposited in human bone as a result of atomic weapons tests, says Libby. Though not proved conclusively, high available calcium seems to reduce the probability of Sr90

being taken up in plants. But the ef­fect does not hold for uptake directly by leaves. Sheep, goats, and cattle feeding on low calcium pastureland, Libby says, do display a higher Sr90

content in bone. Work relating the calcium effect to

Sr90 uptake by humans shows the in­crease in Sr90 in food due to 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 tha t built up from foods grown in the normal soil.

Few individuals, however, accumu­late Sr90 in terms of the available cal­cium of the soil in their region, says Libby. Most people drink milk and eat cheese and other calcium-containing foods, and these reduce the effect of the calcium deficiency. The deficiency is also easily corrected by additions of calcium compounds to the soil.

• Variat ions with Locality. An­other cause of variation in Sr90 content of humans with locality is the amount of fallout in given areas. In the U. S., with higher fallout because of the Ne­vada test site, the northern states have 20 to 30 millicuries of Sr90 per square mile. In the 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 he believes the new data on infants indicate the lower value is more realistic.

Among people living in the same locality, Libby figures only one person in 300 wiil have more than twice the average Sr90 burden. The chances of anyone having as much as three

times the normal burden, he says, will be one in several million.

In evaluating the effect of altitude, Libby compares Sr90 exposure t o cos­mic ray exposure because the physio­logical effects will be the same for the same energy absorbed. He says one sunshine unit equals 3 milliroentgens a year. At this rate the difference be­tween sea level and an altitude of 5000 feet is about 8 sunshine units.

Citing data gathered for 1947 on the occurrence of leukemia and bone cancer in Denver, New Orleans, and San Francisco, Libby says die figures show that other factors are more sig­nificant than cosmic ray dosage. How­ever, he says, they do confirm that the effect of alti tude (8 sunshine units) will not 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 up as changes in the blood. Injury symp­toms are not observed with less than 100 to 200 roentgen exposure. Libby says the 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

SCIENTISTS 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 the opinion of the Study Group on Smok­ing and Health (C&EN, April 8, page 2 7 ) .

The Study Group, organized at the suggestion of the American -Cancer Society, t he American Heart Associa­tion, the National Cancer Institute, and the National Heart Institute, has said, "The sum total of scientific evidence establishes beyond reasonable doubt that cigarette smoking is a causative factor in the rapidly increasing inci­dence of human epidermoid carcinoma of the lung."

Now the 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. The TIRC board says it questions the existence of sufficient definitive evidence to establish a simple cause and effect explanation of the complex problems of lung cancer. It

3 8 C & E N M A Y 13, 1957

feels that the problem of cause of lung cancer by its very nature presents many variables including age, sex, and other biological factors. It also feels that the evaluation of these is further com­plicated b y technical and statistical factors.

 Cancer Cause Observed?

Virus particles "strongly suggestive" to be the cause of breast cancer in mice have been detected with an electron microscope by Leon Dmochowski at the University of Texas M. D. Ander­son Hospital & Tumor Institute, Houston. Also viruslike particles that could be the cause of leukemia have been found.

Dmochowski says that virus particles, of characteristic structure, and inclusion bodies a re observed in the cytoplasm of tumor cells obtained from mice. Virus particles have also been seen in intercellular spaces, he says. He says that although biological tests have failed to prove conclusively that these virus particles are the cause of breast cancer in mice, nevertheless evidence is strongly suggestive. H e finds it interesting that the size of particles with mammary tumor inducing activity, obtained from tumor tissue prepara­tions, falls well within t h e range of the internal dense core of virus particles found in the cells of mammary tumors of mice.

Relationship between these virus particles and the origin of leukemia in mice still remains to be proved. How­ever, the particles are frequently en­countered in leukemia of mice which belong t o different strains and were obtained from different labs.

Understanding tumor-inducing vi­ruses, he feels, may serve as a basis of a search for similar agents in those types of human cancer in which a virus may be one of the originating factors.

One long term project in which Dmochowski is involved is a study of leukemia in mice. He says that cells of various organs of mice affected by leukemia have been found to show under an electron microscope a num­ber of characteristic changes un­noticed in the light microscope. Virus particles have also been found both in and outside the cells of the affected organs.

He says that simultaneously with or preceding the destruction of cell elements, holes form in the cytoplasm of cells. These in turn lead to a com­plete disintegration of the affected cells. At the same t ime or following these changes, characteristic virus par­ticles are formed. These are released into the surrounding cytoplasm and intercellular spaces. •

PRICE LIST

•:i

ioft ^r?

Biochëmiciils^"

NOW RËA&XWi „C* z'pïî ~·*ν ? -^-""^ "*• ^ïif&xi?**

Some SCHWARZ Biochemiccls for Industry and Research

Purines a n d Pyrimidines Phosphorylated Adenosine Compounds Cozymase Nucleosides a n d Nucleotides Nucleic Acids and Metal l ic Nucleates Sugar Phosphates

Glutathione Sulfhydryl Reagents Sugars Triphenyl Tetrazol ium Chloride Deoxynucleosides Optical ly Standardized Amino Acids Radioactive Chemicals

Send the Coupon for your copy

SCHWARZ LABORATORIES, INC. 2 3 0 Washington Street, Mount Vernon, Ν. Υ.

Please send me copy of your 1957 Price List of Biochemicals

Name-

Position.

Company.

Street Address.

City .State.. -Zone.

M A Y 13. 1 9 5 7 C & E N 39

New Text

New TextSCHWARZ 1957