A new study by 15 scientists, statisticians and other experts concludes that more downwind residents suffered thyroid damage from nuclear testing than earlier believed. Also, it says damage was still showing up 30 years after the blasts.
The study's lead author is the University of Utah's Dr. Joseph L. Lyon, who has been pursuing the issue for many years.
In March 2005, the U.S. Centers for Disease Control and Prevention, based in Atlanta, abruptly canceled a study headed by Lyon that involved checking thyroid glands of downwind residents, looking for abnormities.
Thyroid glands accumulated radioactive iodine from milk from grazing cows. Children were most vulnerable.
Four studies have been launched: an examination in 1965-66 of schoolchildren exposed to fallout; an update 30 years after exposure and published in 1993; an attempted 50-year update canceled by the CDC after years of work and millions of dollars; and the new study, which is a re-evaluation of the 1993 report.
The latest is to be published in "Epidemiology," a peer-reviewed scientific journal that is the official publication of the International Society for Environmental
Epidemiology. The study is to be published in the Nov. 1 issue, but an abstract is already online at the journal's Web site, www.epidem.com/pt/re/epidemiology under "Epi Fast-Track."
The title of the article is "Thyroid Disease Associated With Exposure to the Nevada Nuclear Weapons Test Site Radiation: A Re-evaluation Based on Corrected Dosimetry and Examination Data."
The 1993 report concluded there was a connection between radiation from the Test Site and abnormal thyroid growth such as tumors.
In the latest effort, the team, which included radiobiologists, re-examined the data in the 1993 study, correcting mistakes that crept into the original effort. They found an even stronger connection between thyroid abnormalities and fallout.
Errors crept into the study published in 1993 because "there were a lot of uncertainties (about) what people were eating and where they lived and where they moved," Lyon said Wednesday.
Also, problems with the earlier computer system required reconstructing the system. Radiation doses were recalculated. Two computer programmers independently rewrote the algorithm, rechecking each step, Lyon said.
"It took them months," he said.
The re-examination also reviewed all the diagnoses that were reported.
Some diagnoses were changed and others were dropped as not sufficiently documented. This step was more conservative than in the 1993 study.
"We set up very rigid criteria," he said. "What we came up with was a much stronger association with thyroid neoplasms (growths, including tumors). It more than doubled."
The risk ratio for people with the highest exposure to fallout, compared with those with the least exposure, jumped from 3.4 times as likely to develop neoplasms to the new study's 7.5 times as likely.
For thyroiditis, an inflammation that is the most common form of thyroid disorder, the figures also are compelling. Those from heavily hit areas had been thought to be 1.1 times as likely to have the disorder. The new study places the risk ratio at 2.7 times.
"We think that's fairly persuasive that thyroiditis is associated" with fallout exposure, Lyon said. The illness is "a very, very common disease," he added, and the disease is not one the government will make payments for under the Radiation Exposure Compensation Act.
Owen Hoffman, a Ph.D. researcher who heads the SENES Oak Ridge Inc. center for risk analysis at Oak Ridge, Tenn. one of the report's authors said that in the 1993 report, only neoplasms of the thyroid were found to be statistically related to fallout doses.
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