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Environmental disasters and the risk for cancer
Memories of increased incidences linger from Chernobyl and Hiroshima, but the dangers may not be as serious as most fear.
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A colossal earthquake and tsunami damaged Japan’s Fukushima Daiichi nuclear complex on March 11, leading to a meltdown and subsequent radiation exposure second only to the Chernobyl accident 25 years ago. These disasters bring to mind the nuclear attacks on Hiroshima and Nagasaki in 1945, and their subsequent contributions to disease and deaths attributed to radiation exposure.
This year also marks the 1-year anniversary of the BP oil spill in the Gulf of Mexico, an environmental hazard that has exposed area residents to a clear risk for increased cancers, but the amount of that excess risk remains in dispute.
Still in dispute after 25 years
The International Atomic Energy Agency, WHO and the U.N. concluded in a report jointly published in 2005 that fewer than 50 people had died as a direct result of the Chernobyl meltdown. As quoted in a 2006 story in The Lancet, Burton Bennett, chairman of the Chernobyl Forum, the IAEA subcommittee that produced the report, said the reactor explosion was a “very serious accident with major health consequences.” However, the committee did not find a sudden spike in cancers or other diseases. Bennett’s group uncovered 4,000 cases of thyroid cancer they associated with Chernobyl, most in children, but those cancers only resulted in nine deaths.
“We have not found profound negative health impacts to the rest of the population in surrounding areas, nor have we found widespread contamination that would continue to pose a substantial threat to human health, within a few exceptional, restricted areas,” he said.
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Photo courtesy of Evan Douple, PhD |
Greenpeace called the findings “a gross underestimation” and experts in the Ukrainian and Russian governments dismissed the report. Yelena Burlakova, chairwoman of the Council on Radiobiology of the Russian Academy of Sciences, called the IAEA a lobbying group for the nuclear industry, more concerned about protecting power plants than detailing negative health effects associated with radiation.
Incidences of thyroid cancer
A 2008 report from the UN Scientific Committee on the Effects of Atomic Radiation found that more than 6,000 diagnoses of thyroid cancer in younger people were the direct result of exposure to radiation from Chernobyl, a fraction of the 93,000 cases Greenpeace said will eventually appear.
In reality, the health impact of Chernobyl is a bit of a mystery, said Kirsten B. Moysich, PhD, professor of oncology in the department of cancer prevention and control and academic program chair of the department of cancer pathology and prevention at Roswell Park Cancer Institute. More recent, better-designed studies suggest that the risk for cancer was not as great as originally believed, but Moysich said the total number of excess cancers is unknowable.
“I would not want to be quoted putting a number on that. It’s almost impossible to really assess. We know that the people who died of acute exposure is quantifiable, but it is really difficult to quantify the number of excess cancers,” she said in an interview with HemOnc Today. “There were a lot of initial studies that didn’t employ the most rigorous epidemiological study designs, and initially those studies pointed to an increased risk for all types of cancers. The more rigorous epidemiologic studies, many of which were coordinated by the National Cancer Institute, didn’t really point to an excess risk except for thyroid cancer in children and adolescents which … were highly treatable.”
“They appeared in a very young patient population compared with most thyroid cancers, which generally appear in an older population,” said Philip J. McCarthy Jr., MD, professor of oncology and director of the blood and marrow transplant program at Roswell Park. “These children had to undergo toxic therapy as a result of the radiation exposure. For thyroid cancers, there’s approximately a 400-fold increase.”
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Along with Per Hall, PhD, of Karolinska Institute in Stockholm, Moysich and McCarthy wrote an opinion published online April 26 in The Lancet that largely supported the work of the Chernobyl Forum.
“We concluded that, with the exception of thyroid cancer in young people, there was no strong evidence to suggest that excess cancer incidence was substantial in the aftermath of the accident,” they wrote.
In an interview with HemOnc Today, McCarthy and Moysich said that Soviet-era government secrecy kept the outside world from even learning about Chernobyl until days after the meltdown and inhibited efforts to study the immediate health effects. Additionally, there was little experience with long-term epidemiology at the time, and frustrating language barriers, cultural differences and the “daily challenges in covering a very large study area” made it extremely difficult to conduct research.
However, McCarthy, Moysich and Hall concluded that there may have been a “small increase in childhood leukemia incidence,” but there was no evidence that incidence was significantly higher in the areas most affected by radiation from Chernobyl. Additionally, there was no evidence of increased risk for leukemia in adults.
Further studies showed no increase in solid tumor incidence in adults, although there appeared to be an increase in total solid tumor mortality (SIR=1.23; 95% CI, 1.15-1.24). However, Moysich and colleagues said none of the studies reviewed had a follow-up period that corresponded with the latency periods of the tumors in question.
In a review published online by The New England Journal of Medicine in April, Christodouleas and colleagues found that studies conducted among those exposed to radiation from Chernobyl did not show “consistently elevated risks” for leukemia and non-thyroid solid cancers.
There was strong evidence for a two- to fivefold per 1 Gy increased rate of secondary thyroid cancers among children who ingested iodine-131. The increase in relative risk is large, but Christodouleas and colleagues said the baseline incidence of thyroid cancer in children was just one case per 100,000.
Looking back for answers
The nuclear attack on Hiroshima and Nagasaki may provide a better example of the potential health effects of Fukushima. The population has been studied rigorously and extensively in the decades since Fat Man and Little Boy laid waste to the two cities. Research into the health effects associated with Hiroshima and Nagasaki began with the Atomic Bomb Casualty Commission in 1947. The commission was reorganized in 1975 as the Radiation Effects Research Foundation.
The Life Span Study, an epidemiological study, began following 120,000 survivors and control subjects in 1955. The study included the Adult Health Study, a defined subset who would receive additional morbidity surveillance based on biennial health examinations. A third study was initiated to analyze people exposed to radiation in utero, and a fourth to examine a cohort of children conceived after the attack, both those exposed to radiation and their non-exposed counterparts, known as the F1 cohort. Overall, these ongoing studies include more than 200,000 people from the affected areas.
Evan Douple, PhD, is associate chief of research for the Radiation Effects Research Foundation and helped author an article published earlier this year inDisaster Medicine and Public Health Preparedness that looked at risk estimates for radiation-related health effects associated with the bombings. Douple, a professor of medicine at Dartmouth Medical School for 20 years and former director of the biomedical engineering program of the Norris Cotton Cancer Center, said survival 66 years later has been better than researchers expected.
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“Most scientists expected higher rates of cancer and some evidence for radiation-induced mutations in the F1 generation,” he said. “However, an overall excess of around 10% is relatively small and there is still no evidence of increased health effects in the F1. The longevity of the Japanese life span is also amazing until you consider that Japan is one of the longest-living countries in the world.”
Roughly 40% of those who survived the attack are still alive, according to results of the study by Douple and researchers. However, survival is approximately 80% for those exposed before age 20. Researchers said the incidence of cancer will rise in the coming years because people who were younger than 20 years at exposure are becoming elderly and more susceptible to disease.
As of 2002, the most recent published mortality data from the Life Span Study, researchers observed 315 leukemia deaths, 45% of which are estimated to be excess deaths attributable to radiation exposure among the survivors exposed to 0.005 Gy. Risk increases in proportion with dose and reaches about 86% among those exposed to doses of 0.1 Gy.
“The majority of excess leukemia deaths from radiation among those exposed as children occurred during the follow-up period before 1975,” researchers wrote. “There is, however, still evidence of a small increase in leukemia risk among the current survivors and a significant linear radiation dose response for myelodysplastic syndromes, which are characterized by an increased risk of developing acute myeloid leukemia, in A-bomb survivors 40 to 60 years after the radiation exposure.”
Fewer than 1,000 solid cancers can be attributed to the bombings. Of a total of 17,448 solid cancer diagnoses in a sub-cohort of more than 100,000 patients in the Life Span Study, only 853 are thought to be the result of radiation exposure. That represents 11% of all of the solid cancers among survivors exposed to 0.005 Gy. The proportion of cancers attributable to the bombs increases to 48% among those who were exposed to at least 1 Gy.
Researchers found the highest excess relative risk (0.8 or 80%/Gy) for bladder, female breast and lung cancers. Excess relative risk was also relatively high (0.5-0.8 or 50%-80%/Gy) for cancers of the brain/central nervous system, ovary, thyroid, colon and esophagus. A different ranking is obtained when one examines excess absolute risks, which have clinical or public health implications. Excess relative risk for female breast cancer is among the highest in solid cancers at 0.87.
Female breast, stomach, colon, lung, liver, bladder and thyroid cancers have the highest excess absolute risk, which reflects higher numbers of excess cancers. For stomach and liver cancers, the excess relative risk of 0.3 is modestly high, but the excess in absolute risks is extremely high because of the high baseline rates for these cancers in Japan.
Researchers did not find a significant association with radiation exposure for rectal cancer, prostate cancer and malignant melanoma.
Unfortunately, whatever insights that can be gleaned from Hiroshima and Nagasaki must be tempered by the reality that Fukushima is a very different event. The two bombs produced an intense, relatively brief exposure to radiation whereas exposure from Fukushima will be low-level and long-lasting.
“The risk estimates from Hiroshima and Nagasaki represent a worst-case scenario and therefore are very useful as a worst-case scenario for radiation protective standards and for estimating potential health effects,” Douple said.
He added that Japan will likely experience a slight increase in cancer risk over time.
“It would be expected that one would probably not be able to measure a statistically significant excess,” he said. “However, it will depend on the dose information received for the early accident time periods.”
The long-term threat of oil
On the other side of the world, the Gulf oil spill is less likely to present short-term cancer risks like the nuclear events. While the nuclear events show a strong increase in thyroid cancer incidence, and especially among those who were younger at exposure, the risk from the oil spill comes from benzene and polycyclicaromatic hydrocarbons (PAH).
Benzene, found in concentrations of 1% to 6% in crude oil, is a known hematotoxicant and hematocarcinogen. Exposure in this case should be limited because the benzene evaporated before reaching shore, but workers at sea and close to the spill, such as the hundreds of local fishermen hired to work on the cleanup, could be at greater risk for the acute adverse health effects of benzene, depending on the duration of their exposure. Long-term exposure to benzene has been associated with leukemia.
PAH may represent the greater risk for cancer incidence because it is more persistent and can bio-accumulate. PAH is associated with skin and lung cancers, as well as reproductive and developmental toxic effects. A review published in the April 7 issue of The New England Journal of Medicine concluded that although the oil spill workers were likely to experience acute effects due to exposure to PAH and other volatile organic components of crude oil, such as simple aromatics and shorter aliphatic straight-chain hydrocarbons, but that the toxic compounds were probably not present in concentrations great enough to cause long-term health effects.
As many as 52,000 people participated in the cleanup in some capacity, according to the National Institute for Occupational Safety and Health.
Whatever the risks associated with the spill may be, they probably will not appear for years if not decades. Maureen Lichtveld, MD, MPH, Freeport McMoRan chair of environmental policy in the department of environmental health sciences at the Tulane University School of Public Health & Tropical Medicine, said that means it will be extremely difficult to quantify the number of directly associated cancers.
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“Establishing a definite relationship between exposure to environmental contamination and cancer can be very difficult. The few instances we have — asbestos and mesothelioma; benzene and leukemia; PAHs and other cancers; radiological agents and thyroid cancer — are really the exception rather than the rule,” she said. “In most cases, the exposures are a mixture [of elements], making it even harder to discern a definitive association, or a cause-and-effect linkage between environmental exposures and cancers. The work that we have to do begins in the laboratory, but very much ends within our communities.”
That said, Mississippi, Alabama and Louisiana, the states affected by the spill, rank among the worst for a variety of heath indicators, including hypertension, diabetes and cancer mortality associated with breast and prostate cancer, according to The New England Journal of Medicine. Louisiana is home to the infamous “Cancer Alley,” an 85-mile stretch along the Mississippi River between New Orleans and Baton Rouge that is home to several oil refineries and chemical plants, known for a high number of cancer diagnoses and cancer deaths. As of 2002, Louisiana had the second highest rate of cancer deaths in the country at 237.3 per 100,000 population compared with a national average of 206 deaths per 100,000 population.
Considering the current state of health in Louisiana, Lichtveld, who spent 18 years with the CDC in various capacities, including medical officer and senior medical toxicologist, said the oil spill could make the problem worse in an already vulnerable population.
“There have been concerns about cancer clusters in this area, but it is difficult to definitively show that indeed there is an elevated rate of cancer, and therefore, there’s a potential for a double whammy,” said Lichtveld, who is also associate director, Populations Sciences of the Louisiana Cancer Research Consortium. “However, that doesn’t excuse us from being very vigilant in this population and being aware of the historic burden of health disparities.”
Fears likely outstrip the risks
Christopher Busby, PhD, scientific secretary for the European Committee on Radiation Risk, released a report earlier this year estimating that, among the 3 million people living within 3 km of Fukushima, there would be 100,000 excess cancers diagnosed within the next decade and 200,000 excess cancers diagnosed within the next 50 years. In contrast, there were roughly 6,000 thyroid cancers and an unknown number of solid cancers diagnosed in 20 years among the 5 million people living in areas near Chernobyl determined to be contaminated.
Of Busby’s numbers, McCarthy said: “He takes the position that no amount of radiation is safe; that any amount of radiation will cause cancer. He takes a relatively high dose of radiation, which will generate X number of cancers, and just keeps extrapolating down and claiming that, even at a tiny dose of radiation, there will still be an excess cancer risk, even if it’s 100-fold or less. If you’re looking at 100 people, you likely will not see an effect. If you’re looking at 100 million people, that’s how he gets his numbers. We argue about the threshold effect, that risk is minimal below a certain level of exposure. He doesn’t believe that.”
While the cancer risk associated with the Gulf oil spill is unclear, Moysich said the fear regarding nuclear exposure is greater than the actual likelihood of an individual developing cancer due to power plant emissions or a nuclear accident.
“From a public health perspective, compared with obesity or smoking or poor diet, the contribution of a nuclear accident is minimal in terms of cancer risk,” Moysich said. “People are not very introspective about their personal behaviors that contribute to cancer, but it’s the chemical plant down the street or the nuclear power plant accident that will give them cancer. The data suggest the complete opposite.” – by Jason Harris
For more information:
- Busby CC. The health outcome of the Fukushima catastrophe Initial analysis from risk model of the European Committee on Radiation Risk, ECRR. Available at: www.llrc.org/fukushima/subtopic/fukushimariskcalc.pdf. Accessed: May 12, 2011.
- Christiani DC. New Engl J Med. 2011;364:791-793.
- Christodouleas JP. The New Engl J Med. 2011;doi:10.1056/NEJMra1103676.
- Douple EB. Disaster Med Public Health Preparedness. 2011;5:S122-S133.
- Goldstein BD. New Engl J Med. 2011;364:1334-1348.
- Lancet Oncol. 2011; 12:409
- Lyons RA. J. Epidemiol Community Health. 1999;53:306-310.
- Moysich KB. Lancet. 2002;3:269-279.
- Moysich KB. Lancet. 2011;doi:10.1016/S1470-2045(11)70095-X.
- Parfitt T. Lancet. 2006;367:1305-1306.
- Tyson FL. Cancer. 1998;83:1784-1792.
Disclosure: None of the sources in this article reported any relevant financial disclosures.
There are other sources of cancer risk that are of greater concern than radiation associated with nuclear power.
It’s a matter of scale, but, in general, the fear about radiation exposure is greater than the fear of other exposures. Psychologists say it may be linked to one’s control over exposure. It’s a choice to smoke cigarettes or eat a certain diet. It’s not a choice to be exposed to background radiation.
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Those of us who study the cancer risks associated with radiation appreciate that the population is extremely concerned. There are many sources of ionizing radiation; none of us is unexposed. There’s the natural background radiation from radon, gamma rays, cosmic rays. In this country, there are very few people who have not had an X-ray. We know that radiation is cumulative, but the risks associated with natural background radiation and most diagnostic tests are low.
Cancer risks around nuclear power plants have been studied in multiple countries since the early 1980s, if not before. The main focus of that research has been childhood cancer, and specifically childhood leukemia, because children are more sensitive to ionizing radiation. There have been numerous studies in multiple countries covering a large number of nuclear plants. In all of the studies, the results have been that there is no statistically significant association between nuclear power plants and risk for cancer with three notable exceptions: two plants in the United Kingdom — Sellafield and Dounreay, which produces power and reprocesses nuclear fuel — and a third in northern Germany called Krümmel.
Childhood leukemia is the most common form of pediatric cancer, but it is still very rare. From 1990 to 2005, there were 10 cases of pediatric leukemia diagnosed in children younger than 5 years who resided within five kilometers of Krümmel. That’s about five times the number expected based on the German national rate. There is no question that is statistically significant cluster, but in terms of absolute numbers, these excesses are small.
There was a large study conducted in the US and published in 1991 exploring cancer mortality associated with nuclear power. Those researchers concluded there was little evidence of excess, but the authors are clear that they were looking at mortality, not incidence. Particularly when we’re dealing childhood leukemia where survival is so good, you really need to look at incidence.
– Martha S. Linet, MD, MPH
Chief and senior investigator of the NCI Radiation Epidemiology Branch
Disclosure: Dr. Linet reported no relevant financial disclosures.
Jablon S. Cancer in populations living near nuclear facilities: a survey of mortality nationwide and incidence in two states. JAMA. 1991;265:1403-1408.