1. What happened in Hanford, Washington?
The Hanford Nuclear Reservation in the state of Washington released large amounts of iodine-131 and other radioactive materials into the air between 1944 and 1957. After being released into the air, this radioactive material landed on vegetation surrounding Hanford. It also contaminated the air people in the community were breathing. Also, the contaminant was found in the milk of animals living near Hanford, and in the produce grown near Hanford. As a result, the residents who were eating the contaminated produce from Hanford were ingesting some radioactive material.
In the Hanford Birth Cohort Study, people who were born and lived in counties near the Hanford facility between 1945 and 1951 were classified as the exposed group; while those who were born and lived far away from Hanford between 1945 and 1951 were classified as the unexposed group. This study included 1,160 people (487 in the exposed group and 673 people in the unexposed group).
Researchers from the Agency for Toxic Substances and Disease Registry interviewed the exposed and unexposed groups by telephone to find out if they had certain autoimmune or cardiovascular diseases.. The researchers also contacted doctors to find out whether people actually had these diseases. Researchers found that men in the exposed group were about three times more likely to have an autoimmune disease called Hashimoto's thyroiditis, a condition that prevents the thyroid gland from making enough thyroid hormone. This effect was not found in women. In addition, only 48% of the self-reported cases of Hashimoto's thyroiditis could be verified by a doctor. The study did not find that rates of the other autoimmune or cardiovascular diseases studied were different between the exposed and unexposed groups.
2. Details on the study
It is important to note that results from this study are preliminary. In addition, the results have not been peer-reviewed yet. This means that the results of this study have not been reviewed by a series of experts in the field, and have not been published in a scientific journal.
An important limitation of this study is that the method to determine exposure might not be accurate. People were classified into the exposed group because they were born and lived in a county close to Hanford. Residents who lived in the counties close to Hanford were put into one "exposed group," without determining if people within this group actually experienced different levels of exposure. It is possible that some areas of the counties in the "exposed group" that were closer in distance to Hanford received more exposure than areas of the counties in the "exposed group" that were farther away from Hanford. Researchers were not able to get sampling data for the time period when radioactive material was released into the air. Therefore, they were not able to determine exactly how much radioactive material different individuals were exposed to.
Another limitation of this study was possible disease misclassification. Subjects were interviewed about whether they had different cardiovascular and autoimmune diseases. Later, researchers contacted the physicians of study participants to verify self-reported diseases. Not all of the diseases could be confirmed by physicians. Diseases that were only self-reported and not confirmed by physicians might not be accurate.
Due to these limitations, the researchers of this study emphasized that their results do not show that iodine-131 and other radioactive material cause Hashimoto's thyroiditis. Their results show that the rate of Hashimoto's thyroiditis was higher in men of the exposed group than in men of the unexposed groups. But researchers emphasize that other risk factors (not accounted for in this study) for Hashimoto's thyroiditis may be responsible for this increased risk.
3. Why was a health study appropriate in Hanford, Washington?
BASIC QUESTIONS FOR HANFORD, WASHINGTON
Yes, records released by the U.S. Department of Energy in 1986 confirmed that radioactive materials, primarily iodine-131, were released into the air by the Hanford nuclear facility.
Yes, people came into contact with iodine-131 by breathing and ingesting it. Iodine-131 was carried by wind and landed on plants, which cows ate. As a result, the cow's milk contained the iodine-131, and people became exposed by drinking the milk. People also breathed air and ate produce contaminated with iodine-131.
Yes, there is some evidence of an association between this type of exposure and autoimmune diseases. One study showed a significant increase in autoimmune diseases among Japanese atomic bomb survivors. Another pilot study showed that women who had been treated with X-rays for tuberculosis had a higher rate of autoimmune thyroid disease than the control group that had not received this treatment. However, the connection between exposure to radiation and autoimmune thyroid disease is not well established. This study would generate more information about whether there is a relationship between radiation and this disease.
It was suspected that the dose of iodine-131 was high enough to cause a health problem.
The amount of time between the exposure and the study was long enough for the health outcome to develop. The exposure occurred from 1945 to 1951, and the interviews were conducted in 2003.
ADVANCED QUESTIONS FOR HANFORD, WASHINGTON
Yes. The study group was determined from birth records in various counties, during the years people were exposed to radiation from the Hanford Nuclear Reservation. Researchers took a random sample from this study group. Of this random sample, researchers were only able to interview 37% of the study group. This probably occurred because it can be difficult to contact people identified through birth records once they are adults.
Although the approach used in this study has limitations, exposure was classified accurately enough. People who were born in the counties near the Hanford site were considered exposed. People who lived in the counties far away from the Hanford site were considered unexposed.
However, there are significant limitations to this approach that could lead to
exposure misclassification. People in the exposed group were all considered to have the same exposure. Yet, different areas of these counties could have received different amounts of exposure. Air sampling was not conducted during the time of exposure, from 1945 to 1951, so researchers did not know how much radioactive material was actually in the air. Also, no biomarkers were measured among the exposed group, so it is not possible to know exactly how much iodine-131 individual study participants were exposed to.
There may have been some limitations in the classification of health outcomes. Subjects were interviewed about different cardiovascular and autoimmune diseases. Later, researchers contacted the physicians of study participants to verify self-reported diseases. However, less than half (48%), of self-reported diseases were confirmed by physicians. Thus, it is not possible to know the accuracy of self-reported diseases that were not confirmed by physicians.
Researchers interviewed people about their birthplace, lifestyle, diet, and occupation. This means that the study took into account these other factors in this analysis.
Researchers probably considered that the proportion of the exposed population that would develop different cardiovascular and autoimmune diseases was expected to be much higher than that of the unexposed population.Researchers probably took the following steps to plan a study with sufficient
study power.:
- Decided on acceptable levels for level of significance and study power
- Determined how many people from the selected counties were needed to achieve large enough sample size
- Estimated what proportion of the non-exposed population would develop different cardiovascular and autoimmune health outcomes
- Estimated what proportion of the unexposed population would develop different cardiovascular and autoimmune diseases
Before proceeding with the health study, researchers needed to determine whether there was a good chance they would be able to find an increase in cancer rates due to air contamination from the facility.
4. Summary table
| exposure |
Iodine-131 and other radioactive materials from Hanford Nuclear Reservation were released into the air |
| health outcome |
Specific cardiovascular and autoimmune diseases |
| type of study |
Cohort study |
| questions this study seeks to answer |
Is there a higher rate of certain cardiovascular and autoimmune diseases among people born in counties near Hanford than among people born in counties far away from Hanford?Is there evidence that exposure to iodine-131 and other radioactive materials may be related to increased rates of certain cardiovascular and autoimmune diseases? |
| target population |
People who were born in counties near HanfordPeople who were born in counties farther from Hanford |
| data collected and methodology |
Telephone interview asking people if they had certain diseases |
| data analysis |
Rates of specific diseases were compared among exposed and unexposed groups |
strengths
of this study |
Gathered more information about rates of certain cardiovascular and autoimmune diseases among those likely exposed to radioactive materialResponded to concerns of community members about the relationship between iodine-131 and certain diseases |
limitations
of this study |
Researchers emphasized that this study was not designed to prove that exposure to iodine-131 causes certain cardiovascular and autoimmune diseasesIndividual exposure to iodine-131 was not measuredNot all of the self-reported illnesses could be verified by the participants' doctors |