Three Mile Island accident health effects

In the aftermath of the accident, the investigations focused on the amounts of radioactivity released by the accident. American Nuclear Society explained using the official radioactivity emission figures that "the average radiation dose to people living within ten miles of the plant was eight millirem, and no more than 100 millirem to any single individual. Eight millirem is about equal to a chest X-ray, and 100 millirem is about a third of the average background level of radiation received by US residents in a year".[1][10] To put this dose into context, while the average background radiation in the US is about 360 millirem per year, the Nuclear Regulatory Commission regulates all workers' of any US nuclear power plant exposure to radiation to a total of 5000 millirem per year.[11] Based on these low emission figures, early scientific publications on the health effects of the fallout estimated one or two additional cancer deaths in the 10-mile area around TMI.[8]

In 1990-1 a Columbia University team, led by Maureen Hatch, carried out the first epidemiological study on local death rates before and after the accident, for the period 1975-1985, for the 10-mile area around TMI.[3][19] Assigning fallout impact based on winds on the morning of March 28, 1979,[3] the study found no link between fallout and cancer risk.[8] The study found that cancer rates near the Three Mile Island plant peaked in 1982-3, but their mathematical model did not account for the observed increase in cancer rates, since they argued that latency periods for cancer are much longer than three years. From 1975 to 1979 there were 1,722 reported cases of cancer, and between 1981 and 1985 there were 2,831, signifying a 64 percent increase after the meltdown.[21] The study concludes that stress may have been a factor (though no specific biological mechanism was identified), and speculated that changes in cancer screening were more important.[19]

On the recommendation of the Columbia team, the TMI Public Health Fund followed up its work with a longitudinal study.[23] The 2000-3 University of Pittsburgh study[24] compared post-TMI death rates in different parts of the local area, again using the wind direction on the morning of 28 March to assign fallout impact, In contrast to the Columbia study, which estimated exposure in 69 areas, the Pittsburgh study drew on the TMI Population Registry, compiled by the Pennsylvania Department of Health. This was based on radiation exposure information on 93% of the population living within five miles of the nuclear plant - nearly 36,000 people, gathered in door-to-door surveys shortly after the accident.[25] The study found slight increases in cancer and mortality rates but "no consistent evidence" of causation by TMI.[24] Wing et al. criticized the Pittsburgh study for making the same assumption as Columbia: that the official statistics on low doses of radiation were correct - leading to a study "in which the null hypothesis cannot be rejected due to a priori assumptions."[26] Hatch et al. noted that their assumption had been backed up by dosimeter data,[23] though Wing et al. noted the incompleteness of this data, particularly for releases early on.[27]

In 2005 R. William Field, an epidemiologist at the University of Iowa, who first described radioactive contamination of the wild food chain from the accident suggested that some of the increased cancer rates noted around TMI were related to the area's very high levels of natural radon, noting that according to a 1994 EPA study, the Pennsylvania counties around TMI have the highest regional screening radon concentrations in the 38 states surveyed.[28] The factor had also been considered by the Pittsburgh study[24] and by the Columbia team, which had noted that "rates of childhood leukemia in the Three Mile Island area are low compared with national and regional rates."[3] A 2006 study on the standard mortality rate in children in 34 counties downwind of TMI found an increase in the rate (for cancers other than leukemia) from 0.83 (1979–83) to 1.17 (1984–88), meaning a rise from below the national average to above it.[22]

A paper in 2008 studying thyroid cancer in the region found rates as expected in the county in which the reactor is located, and significantly higher than expected rates in two neighboring counties beginning in 1990 and 1995 respectively. The research notes that "These findings, however, do not provide a causal link to the TMI accident."[29] According to Joseph Mangano (who is a member of The Radiation and Public Health Project, an organization with little credibility amongst epidemiologists,[30]) three large gaps in the literature include: no study has focused on infant mortality data, or on data from outside the 10-mile zone, or on radioisotopes other than iodine, krypton, and xenon.[8]