Gould, Ernest J. Sternglass, Janette D. Sherman,
From 1954 to 1964, average picocuries of Sr-90 per gram calcium in the vertebrae of New York adults rose from under 0.1 to 2.2, more than a twenty-fold increase. The estimated dietary uptake of Sr-90 in adults rose thirty-fold, from 1 picocurie per gram of calcium in 1954 to 29.8 in 1964. The 1964 peak in Sr-90 concentration occurred just after ratification of the Partial Test Ban Treaty by the U.S. that ended American, British, and Soviet atmospheric nuclear weapons tests, while a relatively small number of French and Chinese tests continued. (Underground tests replaced atmospheric tests in the nations that signed the treaty). Thereafter, levels in New York and San Francisco declined sharply after the cessation of testing above ground. In the years 1964-70, dietary uptake of Sr-90 in adults declined on average by 15.7 percent each year. The Public Health Service's data show a similar increase and decline before and after the peak of 1964. Federal support for this effort was withdrawn in 1971.
The U.S. government also participated in a study measuring Sr-90 concentrations in the baby teeth of about 60,000 children by the St. Louis-based Committee for Nuclear Information (CNI) begun in 1958. The use of baby teeth made it simple to collect large samples, rather than relying on autopsy results. (5) The baby tooth analysis showed a rise from 0.77 pCi Sr-90/g Ca for 1954 births to a peak of 11.03 for 1964 births, just after the Test Ban Treaty. (6) From 1964 to 1970, Sr-90 in St. Louis baby teeth fell by more than half (Figure 1), about the same average annual rate of decline (15.7 percent) displayed by adult uptake in those years (Figure 2). One exception to this pattern took place from 1958 to 1961, when the U.S. and U.S.S.R. observed a voluntary moratorium on nuclear testing.
In the early 1950s, average concentrations of Sr-90 in teeth increased moderately, but began to rise more rapidly after 1954 with the sharp elevation of Sr-90 from thermonuclear bomb tests, the fallout from which ascended into the stratosphere and returned to earth via precipitation over a two or three year period. After the moratorium that began in late 1958, atomic and hydrogen bomb tests were resumed in the fall of 1961, with the detonation of a 50 megaton bomb by the U.S.S.R. in northern Siberia, equal to more than 3000 Hiroshima bombs. (7)
Trends in Sr-90 in baby teeth from 1960 to 1970 are significantly correlated (r = .78, P<.001) with temporal changes in cancer incidence among children age 0-4 (each year actually represents a three year moving average) in Connecticut, the only state with an established tumor registry during this period. Because trends in Sr-90 concentrations in St. Louis milk are similar to those in Hartford, Connecticut and elsewhere in the U.S., (8) similar temporal changes of radioactivity in teeth can be assumed for the entire nation. Childhood cancer in Connecticut reached a peak in 1964, before plummeting in the latter half of the 1960s. The CNI study ended in the early 1970s, when federal support for the project ceased.
The high correlation between radioactivity in baby teeth and cancer in young children in the period 1954-70 is paralleled by a similar relationship with the adult dietary uptake of Sr-90 as estimated by the U.S. Department of Energy, the successor to the AEC, from 1954 to 1982. (3)
In Figure 2 the correlation coefficient between childhood cancer and adult dietary uptake of Sr-90 is .79 (P<.001) for the years 1960 to 1970, the period when the latter indicator reflected the high Sr-90 levels in the diets of pregnant women.
Both Figures 1 and 2 support the well-known fact that exposure to toxic agents is most harmful to the developing embryo and fetus, both in humans and in animals. Throughout intrauterine life, the developing fetus undergoes rapid cell growth, self-programmed cell death (apoptosis), and cell rearrangement. The developing infant is similarly susceptible to cellular and metabolic damage. Unrepaired damage to the rapidly growing and re-arranging fetal cells becomes magnified with time, increasing the risk of cancer, congenital malformations, underweight births, brain damage, and fetal/infant deaths. (9)
At ten weeks of development when the fetus is a little over 1.5 inches in length, the enamel organs and dental papillae form. Some formation begins two weeks earlier. (10) Stem cells of hematopoietic system originate in the bone marrow at about 12 weeks of prenatal development, (11) giving rise to the B-lymphocytes whose progeny make humeral antibodies, and the T-lymphocytes involved in cellular immune responses. (12)
Fetuses can be harmed by very low dose radiation, first demonstrated in the 1950s when exposure to pelvic X-rays in utero was linked with elevated levels of leukemia and cancer deaths before age ten. (13) (14)
U.S. health officials have not monitored radioactivity in humans since 1982. Moreover, the Environmental Protection Agency (EPA) program of reporting barium-140, cesium-137, and iodine-131 in pasteurized milk for each of 60 U.S. cities ceased in 1990 after 33 years of operation. (15) While the last worldwide atmospheric weapons test was detonated in China in 1980, the presence of nuclear power reactors has grown in the past two decades. From 1982 to 1991, the number of operating U.S. reactors increased from 72 to 111, providing power in 32 of 50 states (in which 85% of the 1990 U.S. population resides), and electricity generation by these plants increased from 278,000 to 613,000 gigawatt hours, before leveling off in the 1990s. (16) During this period, cancer incidence in 11 U.S. states and cities rose 40.4% for children age 0-4, and 53.7% for those under one year, a time when average levels of Cs-137 and I-131 doubled. (17)
Continuing measurements of in vivo radioactivity in other nations have revealed unexpected and significant trends. West German researchers documented a ten-fold increase in Sr-90 in baby teeth for children born in 1987 compared to those born in 1983-85, due to fallout from the Chernobyl accident, a relative increase comparable to that observed in St. Louis from 1954-64. (18)
Without a system of monitoring the presence of key radioactive isotopes such as Sr-90 in the human body, no definitive assessment of health effects of exposure to man-made radioactivity can be made. The average annual decline in adult Sr-90 uptake after 1970 was only about five percent, as compared with the 15.7 percent annual decline in Sr-90 uptake levels in adults from 1964-70 (3), reflecting perhaps the proliferation of large nuclear power reactors in the 1970s and emissions from flawed underground tests. Cancer incidence age 0 to 4 in Connecticut - a small state with four operating nuclear reactors - which was as low as 14.42 per 100,000 in the late 1960s, had reached 21.95 per 100,000 in the late 1980s, a jump of over 52%. (19)
This trend suggests that additional recent data on in vivo radioactivity in the U.S. are needed, particularly in the light of the puzzling decision of the DOE to terminate measures of Sr-90 in adults in 1982. In that year, dietary levels of the Sr-90 uptake remained at the same level of 5.6 pCi/g Ca as in 1981, comparable to the late 1950s. The last DOE report observed "There has been some indication of slightly higher values for young adults during the last several years. These individuals were children during the period of greatest Sr-90 deposition." One might presume from this statement that adult Sr-90 levels would rise in the 1980s and 1990s as baby boomers account for increasing proportions of the adult population and as an increasing number of nuclear power plants came on line. (3)