Cancer Rates Drop After Nuclear Reactor Closes

Roxanne Nelson

April 03, 2013

The closure of a nuclear reactor could be linked to a long-term decrease in the incidence of cancer.

Since the Rancho Seco nuclear reactor, located in Sacramento County, California, closed in 1989, there have been several thousand fewer cancer deaths in the region.

Results from the first long-term study to examine the impact of the closure of a nuclear reactor on health were published online March 27 in Biomedicine International.

The research was conducted by Joseph Mangano, MPH, MBA, an epidemiologist and executive director of the radiation and public health project in New York City, and Janette Sherman, MD, adjunct professor of environmental studies at Western Michigan University in Kalamazoo.

"We believe that further research is now warranted to see if there is a cause and effect relation between the elimination of nuclear emissions from power plants and a significant long-term decline of cancers," Mangano said during a press briefing.

The Rancho Seco reactor was chosen for the study because of the long post-shutdown period, the availability of county-specific incidence data since before the plant closed, and the fact that there are no other major reactors within 200 miles, he explained.

In addition, because the Sacramento area uses more electricity from renewable nonpolluting sources than other areas in California, the researchers hypothesized that there would be less pollution from other power sources influencing their results.

Slow Decline in Incidence

In the final 2 years of the reactor's operation (1988-1989), there were 8234 diagnosed cases of cancer. The standard incidence ratio (SIR) in Sacramento County, compared with the entire state, was 1.0760. There was a steady decline in SIRs over the 2 subsequent 5-year periods (1990-1994 SIR, 1.0440; 1995-1999 SIR, 1.0272), and then a leveling off in 2000-2004 (SIR, 1.0346) and 2005-2009 (SIR, 1.0359). These SIRs were all significantly different from the 1988-1989 SIR (P < .05).

If the SIR had remained at the 1988-1989 level over the 20-year period, there would have been 4319 more people diagnosed with cancer, the researchers report.

Over the 20-year period, the ranking of the annual cancer incident rate in Sacramento County, among all 47 California counties, fell from 7 to 22.

SIRs for 13 of the 16 most common cancers declined during the 20-year period.

Thyroid and Breast Cancers Dropped

There were statistically significant decreases in SIRs for female breast and thyroid cancer; for female breast cancer in situ, the decrease was of borderline significance. In Hiroshima and Nagasaki survivors, these were the cancers with the highest excess relative risk from 1958 to 1987.

The incidence of thyroid cancer in Sacramento County in the 1990s remained near 1989 levels. However, in the 2000s, the SIR for thyroid cancer fell below 1.0, indicating that the rate in Sacramento County was lower than that in California overall.

"The study shows that even relatively low-dose radiation exposure in the United States may have harmed humans," said Mangano.

Developing fetuses and infants are most susceptible to cellular damage from radiation exposure. Therefore, when researchers study the health risks of nuclear plants, cancer in children is the most studied type of malignancy.

From 1988-1989 to 1990-1994, the rate of cancer in Sacramento County children declined from 17.92 to 15.49 cases per 100,000 population (11.7% reduction). During the same period, the rate in the rest of the state remained virtually unchanged. Rates in Sacramento County children began to rise in 2005-2009, although were still lower than they were in 1988-1989.

Thyroid Disease Rising After Fukushima

Mangano and Dr. Sherman conducted another study of nuclear reactors, which was published in the March issue of the Open Journal of Pediatrics. They examined the effects being felt in the United States after the March 11, 2011 earthquake caused meltdowns in 4 reactors at the Fukushima Daiichi plant in Japan. Just days after the meltdowns, precipitation in the United States was found to have levels of iodine-131 more than 200 times the normal range.

The highest levels of iodine-131 were documented in the 5 states on the Pacific Ocean.

The researchers looked at cases of congenital hypothyroidism in these 5 states from March to December, and found that the number was 16% higher in 2011 than in 2010. During this same period, the number declined 3% in 36 other states (< .03).

"Fetuses and newborns are especially vulnerable to radiation exposure. Those with hypothyroidism must be treated promptly or they will suffer from dwarfism and mental retardation," explained Dr. Sherman.

The researchers have disclosed no relevant financial relationships.

Biomed Int. Published online March 27, 2013. Abstract

Open Journal of Pediatrics. 2013;3,1-9. Abstract

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