A SHORT LATENCY BETWEEN RADIATION
EXPOSURE FROM NUCLEAR PLANTS AND CANCER IN YOUNG CHILDREN
Even at relatively low doses, irradiated adults are at greater risk for cancer just several years after exposure. A peak of chronic myeloid leukemia incidence was observed 6-10 years after Xrays to the back, gastrointestinal tract, and kidneys. (13) Mormon families in Utah living directly downwind of atmospheric nuclear weapons tests in Nevada were found to have significantly higher incidence of all cancers combined and certain radiosensitive tumors 7-15 years after the tests began. (14) Four to five years after the Chernobyl accident, thyroid cancer among adults in the Czech Republic and Poland increased. (15-16)
The developing fetus and infant has demonstrated a predisposition to cancer from various types of low-dose radiation exposure within a decade. Pelvic X-rays to pregnant women in the 1950s initially was linked to a near-doubling of the risk of cancer death before age ten. (17-18) Subsequent reports on larger populations confirmed this excess, both for leukemia and other childhood cancers. (19-21)
Elevated levels of radiosensitive cancers in the young shortly after exposure to atmospheric nuclear weapons test fallout have also been documented. Peaks in acute myeloid leukemia deaths in U.S. children age 5-9 occurred in 1962 and 1968, about five years after the peak testing periods of the late 1950s and early 1960s. (22) From 1948-1952 to 1958-1862, the number of Utah residents under age 30 who had their cancerous thyroid gland removed surgically rose from 6 to 30, much faster than the national increase. (23) In five Nordic countries, leukemia incidence in children under age five peaked during the highest periods of fallout from bomb tests. (24)
More recently, an elevation in leukemia diagnosed in the first year of life was seen in children born in 1986 and 1987, just after the accident at Chernobyl, representing a latency period of less than two years between in-utero exposure and diagnosis. These elevations were documented in multiple nations, including Belarus (25), Greece (26), Scotland (27), the U.S. (28), Wales (29), and West Germany (30), plus a grouping of European countries. (31) A latency beginning just four years between the accident at Chernobyl and elevated thyroid cancer rates in children has been reported in Belarus and the Ukraine. (32-34) Rising thyroid cancer incidence in children has also been reported within ten years of the accident in the moderately exposed areas of Belgium (35), East Hungary (36), and northern England (37). While some reports have found no excess in non-thyroid cancers in children irradiated by Chernobyl fallout, elevated rates within ten years of exposure have been documented in the Ukraine (38) and Turkey. (39)
Other reports have found unexpectedly high rates of childhood cancer, often leukemia and typically diagnosed before age ten, near nuclear installations. Early childhood cancer near nuclear plants likely represents effects of exposures in utero and in infancy. In the United Kingdom alone, at least eleven such reports representing different nuclear plants exist. (40-50) Similar results were observed in Canada (51), France (52), Germany (53), and the former Soviet Union. (54) Reports on this topic from the U.S. have been limited to several examining populations near a single facility at least two decades ago. (55-59) Data from a 1990 National Cancer Institute report show that cancer incidence age 0-9 near each of four U.S. reactors exceed the state rate. (60) A recent analysis shows that cancer incidence age 0-9 within 30 miles of each of 14 U.S. plants exceeds the national average for 1988-1997, based on 3669 cases. (61)
The many reports documenting a 5-10 year lag between radiation exposure and childhood cancer onset, plus elevated childhood cancer near nuclear power plants, illustrate the heightened sensitivity of the fetus and infant to toxins. This report will further examine this susceptibility by analyzing temporal trends in childhood cancer in populations exposed to low-dose nuclear power plant emissions 5-10 years after initial exposure.
Because of the expected brief latency between exposure and disease onset, cancer deaths age 0-9 in the periods 1-5 and 6-10 years after startup (used in the 1990 National Cancer Institute study of 52 U.S. nuclear power plants) can serve as controls and cases, respectively. Temporal changes in the Standard Mortality Ratio (SMR), representing the ratio of observed to expected (local vs. national) rates, will be examined. Significance of differences in observed and expected changes will be tested using a standard z-score test.
The four exposed groups in the study are:
1. Three Mile Island
Cancer mortality for children age 0-9 residing in the 34 contiguous counties north and northeast of Three Mile Island will be studied. (see Appendix 1) Of these, 28 are in Pennsylvania and 6 in New Jersey, and all lie within 130 miles of the plant. SMRs in the period 1979-1983 (1-5 years after the accident) and 1984-1988 (6-10 years after) will be compared. ICD-9 diagnosis codes 140.0 – 239.9 are used to identify all cancers combined, in all four study groups in this report. SMR changes for leukemia (ICD-9 204.0 – 208.9) and all other cancers combined will also be reviewed.
U.S. government measurements during May and June identified areas of the country that received the greatest levels of Chernobyl fallout. The upper Midwest and Pacific northwest, along with New York City, Washington DC, and Maine, had the highest concentrations of iodine-131 (half life of 8.05 days) in pasteurized milk from May 6 – June 30. (Table 1)
3. Counties near New Nuclear
Plants – Startup Before 1982
4. Counties Near New Nuclear
Plants – Startup Since 1982
Of the areas proximate to these 23 plants, the most populated 14 (with 88% of the childhood cancer deaths a decade after startup) were selected for study. One of these, near the Catwaba plant in South Carolina, was excluded from the analysis, since it lies close to the McGuire plant, which began operations four years before Catawba startup, and is included in the previous analysis. Over 17.5 million Americans lived in counties proximate to these plants in 2000 (Table 3). The SMR for childhood cancer age 0-9 for the periods 1-5 years and 6-10 years after startup will be compared near each plant. If a plant began operations in 1982, the periods 1983-1987 and 1988-1992 will be used.
The second part of this report examines the effects of radioactive emissions, as detected in the bodies of children. The average Strontium-90 concentration in baby teeth was measured for over 4,000 American children, most residing near nuclear power plants. The ratio of Sr-90 per gram of calcium at birth in each baby tooth was measured in a radiochemistry laboratory, using a scintillation counting technique.
Average Sr-90 concentrations were analyzed by the birth year of the tooth donor, since much of the Sr-90 uptake in deciduous teeth occurs during pregnancy and early infancy. Temporal trends in Sr-90 averages were compared with trends in cancer incidence for children under age ten in counties near nuclear plants with the largest numbers of teeth. These plants include Suffolk County NY (near the Brookhaven National Laboratories); Monmouth and Ocean Counties NJ (near the Oyster Creek plant); and Putnam, Rockland, and Westchester NY Counties (near the Indian Point plant). The correlation between these two trends will be assessed using a Poisson regression analysis testing the hypothesis that they are related. Linear and quadratic correlations will be tested, using the actual value, square root, and fourth root of Sr-90 averages.
The specific methodology to calculate Sr-90 concentrations for each tooth has been described previously (66) (67). Teeth from Suffolk County were analyzed using a Wallac WDY 1220X Quantulus low-level scintillation spectrometer, while a Perkin-Elmer 1220-003 Quantulus Ultra Low-Level Liquid Scintillation Spectrometer was used for other teeth. In addition, the method used to clean teeth before testing differed between Suffolk and other teeth; a more sophisticated preparation for non-Suffolk teeth, plus use of a different counter, allowed more Sr-90 to be detected. However, results for each area are internally consistent, allowing Sr-90 patterns and trends to be analyzed.
Sr-90 results are compared with cancer incidence diagnosed in children age 0-9 who resided in counties near nuclear plants at the time of diagnosis. Cancer registries from the states of New Jersey and New York provided counts of incident cases, while the U.S. Census Bureau counts and inter-censal estimates for resident population were used. Three-year moving averages, rather than individual years, are used for both Sr-90 and cancer rates, to increase statistical power of the comparison.
1. Three Mile Island
3. Counties Near Nuclear
Plants (startup before 1982)
4. Counties Near Nuclear
Plants (startup since 1982)
In the United States, the issue of whether nuclear reactor operations have affected childhood cancer risk is largely unexamined. This is a pertinent area of study, since atmospheric and subterranean weapons tests ceased in 1963 and 1992, respectively. The 103 U.S. nuclear power reactors now in operation represent nearly one-fourth of the world’s total, and include some of the oldest reactors.
This report analyzes cancer mortality in children exposed to radioactivity from nuclear power reactors who died before their tenth birthday. Because the lag between exposure and diagnosis is often 5-10 years, the periods 1-5 years and 6-10 years after initial exposure were compared. Excess cancer deaths among children during the first five years after exposure would not be expected, and thus represent a control group, while an elevated level of cancer deaths 6-10 years after exposure would be expected.
In areas of the U.S. exposed to the greatest levels of fallout from accidents at Three Mile Island and Chernobyl, and areas proximate to newly-started nuclear reactors, increases in the Standard Mortality Ratio 6-10 years after initial exposure in children under age ten were observed. Increases in SMR ranged from 8.7% to 23.8% (see Figure 1); each of these temporal changes achieved or approached statistical significance. For each of the four areas studied other than the area near Three Mile Island, the SMR increase for leukemia exceeded that for all other cancers. SMRs were all less than 1.00 in the period 1-5 years after initial exposure, and were greater than 1.00 in the period 6-10 years after; this indicates that populations with cancer rates below the national average changed to those above the national standard in just a few years.
In addition, the report examines the relationship between temporal trends in-body radioactivity (i.e. Sr-90 in baby teeth at birth) and childhood cancer incidence near three U.S. nuclear installations. For each area, the pattern of childhood cancer increasing 4-5 years after a rise in Sr-90 (and decreasing 4-5 years after a Sr-90 decline) was consistent. While the relationship achieved statistical significance in just two of the three areas, plus all three areas combined, the link between fetal/infant exposures from nuclear plant emissions and cancer in childhood is suggested. Much of the Sr-90 in deciduous teeth for children living near nuclear plants probably represents emissions from the plant that is ingested in air and food. (67)
An important finding in the analysis of Sr-90 and childhood cancer trends is that the quadratic (fourth root) value of Sr-90 in baby teeth provides the highest incidence rate ratio, and thus supports the theory that a quadratic of Sr-90 fits the assumption of a link better than linearity. Thus, the upward supralinear dose-response best describes the relationship between in-body Sr-90 and childhood cancer risk. This relationship indicates that the greatest per-dose risk occurs at the lowest dose levels, which is a critical aspect of understanding health risks of radioactive environmental emissions routinely released from nuclear facilities.
This report represents an in-depth examination of temporal childhood cancer patterns near U.S. nuclear plants. The findings are important in several ways. They support the pattern of a relatively short lag period between exposures early in life and disease onset. The pattern of children exposed to radiation being especially susceptible to leukemia as opposed to other types of cancer is consistent with many earlier findings.
Perhaps the most important aspect of the report is documentation of an apparent childhood cancer risk at relatively low levels of exposure. Many previous studies involved considerably larger doses, including fallout from atomic bomb tests and radiation from the Chernobyl accident. Radioactivity in the U.S. from the Three Mile Island and Chernobyl accidents were considerably less than that in Belarus/Ukraine after Chernobyl. While environmental emissions of fission products from nuclear plants vary, they are typically lower than those involved in major accidents or bomb test fallout.
Results indicate that ongoing exposure to radioactivity may present an increased health risk to infants and children not previously understood. Exposures like Hiroshima and X-rays represent a single dose, while nuclear plant emissions are continuous, and long lived isotopes from Three Mile Island/Chernobyl remained in the U.S. food chain for several years.
The study has limitations that should be addressed in subsequent research efforts. Perhaps the most important of these is the need to continue to improve dose estimates for exposures from nuclear plant emissions; and the need to further explore epidemiological comparisons of health risk. A case-control comparison of in-body doses of radioactivity in children with and without a disease such as cancer living proximate to nuclear facilities would be useful to fill this need. This report isolates only one specific type of cancer (leukemia). It examines only potential effects on young children, not adolescents or adults. It examines patterns of cancer mortality only in the first decade after initial exposure, and not thereafter. Not all increases in SMR, or the correlation between Sr-90 in baby teeth and childhood cancer incidence, are statistically significant.
Despite these shortcomings, the epidemiological findings documented here represent an important contribution to the understanding of radiation risks to the very young. With tens of millions of Americans living proximate to nuclear reactors, more detailed studies should be pursued forthwith.
The author wishes to thank Araceli Busby, PhD, for her assistance with statistical significance testing for this manuscript.
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Joseph J. Mangano MPH MBA is National Coordinator of the Radiation and Public Health Project, a research group based in New York.