Radioactivity released during the Three Mile Island (TMI) accident in 1979 does not appear to have caused an increase in cancer mortality among people living within a five-mile radius of the nuclear accident, according to researchers at the University of Pittsburgh''s Graduate School of Public Health.
While several follow-up studies on the TMI population have been conducted in the past, this one is the most extensive due to its longer, 13-year time-frame and the use of information about residents'' lifestyles and everyday radiation exposure beyond what was caused by the TMI incident.
"This study helps put to rest the lingering question of whether the residents of Three Mile Island are experiencing an increase in cancer deaths as a result of the nuclear accident," said Dr. Evelyn Talbott, associate professor and principal investigator on the study.
The TMI incident occurred at a nuclear power plant near Harrisburg, Pa., on March 29, 1979, when a reactor leaked small amounts of radioactive gases.
It is often referred to as the worst nuclear accident in American history.
Scientists have calculated that the average person present in the area during the 10 days after the incident was exposed to considerably less radiation than the annual dose an individual receives from the everyday environment in the United States.
The University of Pittsburgh study covered the years 1979 to 1992.
Researchers collected information on education, occupational, smoking status, residential history, medical history, previous radiation exposure and daily travel in and out of the area during the 10 days following the accident from 32,135 individuals.
The researchers found no consistent evidence suggesting that the low-dose radiation released during the TMI accident had a measurable impact on the mortality of those living in the are for 13 years after the event.
For example, elevations in mortality from cancers of the bronchus, trachea and lung were observed in women, as well as an increase in lymphatic cancers in men, even after controlling for background radiation exposure, education and smoking. However, neither showed a significant does-response trend.
Likewise, investigators noted an increasing pattern of relative risk for breast cancer in relation to increasing levels of likely exposure to gamma radiation, suggesting a possible link between dose of radiation and increased risk.
However, they concluded that overall there was no significant relationship between likely exposure to gamma radiation and breast cancer mortality.
"A relationship between gamma radiation and breast cancer has been noted in other investigations, but emissions from the TMI incident were significantly lower than in other documented studies," said Talbott. "Therefore, it is unlikely that this observed dose trend is related to radiation exposure on the day of the accident."
Although the researchers found no significant evidence showing an increase in cancer death from the TMI accident, they acknowledged that further study is warranted.
"Because the latency period for many cancers is 20 years or more, continued follow-up on the TMI residents will provide a more comprehensive look at their mortality, as well as morbidity, from various cancers," said Talbott.
The University of Pittsburgh research team is currently analyzing data collected through 1999 on the same population.
by Virginia Sutcliffe