Wahab and Co-Workers Explained:
Elevated Chromosome Translocation Frequencies in New Zealand Nuclear Test Veterans.
Reference: Wahab, M.A., Nickless, E.M., Najar-M’Kachar, R., Parmentier, C., Podd, J.V. and Rowland, R.E. (2008) Elevated Chromosome Translocation Frequencies in New Zealand Nuclear Test Veterans, Cytogenetic and Genome Research, 121, pp. 79-87.
What were the research questions?
Scientists in laboratories world-wide use abnormal chromosomes, such as reciprocal translocations and dicentrics, as evidence that individuals have been exposed to ionising radiation. The researchers in this study wanted to establish whether New Zealand naval veterans were exposed to radiation as a consequence of participating in a series of nuclear tests called Operation Grapple which took place in the Pacific in 1957-1958. These veterans served aboard the frigates HMNZ Pukaki and Rotoiti which were stationed at various distances between 20 and 150 nautical miles from ground zero for the various tests.
How was the scientific problem approached?
The research team sought to compare chromosomes from the lymphocytes (white blood cells) of N.Z. naval veterans with a control group to see if the naval veterans had higher levels of abnormal chromosomes. In particular, they were interested in reciprocal translocations as these persist in the body several years after exposure.
The research team decided not to include naval veterans in their control group. The researchers highlighted that the New Zealand Navy was relatively small, meaning that naval personnel who were not part of Operation Grapple may have served aboard potentially contaminated ships. Instead the authors recruited the control group from men who had served in the military (mostly ex-army) or in the police, to control for the healthy soldier effect. This effect recognises that veterans have better health than the general public, because they are healthier at enlistment, must maintain good health during military service and receive good healthcare both during and after their service.
What did the research involve?
The researchers randomly selected 50 naval veterans of Operation Grapple who were aboard the HMNZ Pukaki and Rotoiti and 49 control group members for the study who complied with pre-defined criteria. All of this information was ascertained by through the use of questionnaires.
Potential participants were excluded if they 1) had served in a war or in a nuclear-related area, 2) were exposed to other toxic, DNA-damaging substances, 3) received radiotherapy or chemotherapy, 4) were over 75 years old, 5) had been air force aircrew, 6) were too poorly to participate, or 7) those who passed away before the survey was completed.
The controls were age-matched with the Grapple veterans since the levels of certain abnormal chromosomes such as reciprocal translocations vary with age.
Recruited participants donated blood which was processed for 72 hours, longer than the standard culture time, before being assayed to identify and count abnormal chromosomes using the technique called M-FISH (multiplex fluorescence in situ hybridisation).
The authors performed what they described as “rough retrospective biological dosimetry” by exposing blood samples from a healthy volunteer to known doses of X-rays to generate a graph called a dose response curve. They then used this curve to estimate the dose that the veterans had received.
What did they find?
The researchers found that as a group, the nuclear test veterans had approximately three times the level of translocations (2.9 per 100 cells) in a sample of their blood compared to the control group (1.0 per 100 cells). The highest number of translocations found in an exposed veteran was ~6 per 100 cells and in a control was ~3 per 100 cells; the occurrence ranged from 0~6 and 0-3 in the two groups. The test veterans also had a higher ratio of incomplete to complete translocations (136:94) than the controls (44:45).
In addition, there were 12 dicentrics and 77 acentrics in the exposed group and only 1 dicentric and 48 acentrics in the control group. There were other cells with dicentric and acentric chromosomes but were in cells also containing complex chromosome aberrations, so were not counted.
There were 37 cells with complex chromosome rearrangements in a randomly selected group of 10 of the exposed veterans and less than 10 cells like this were observed in the entire control group.
How did the researchers interpret their basic results?
The researchers considered their data as likely to be evidence that the New Zealand nuclear test veterans had been exposed to radiation due to their participation during Operation Grapple. They also estimated the average dose received by the veterans to be 170 mGy and that an average dose of 37 mGy was received by the control group. The authors do not know the type of radiation that the veterans received or how many times they may have been exposed.
The researchers considered the possibility that their study could have been confounded by a variable relating to service on a naval vessel, e.g. the elevated levels of translocations could be due to exposure to chemicals in paint on the ships, given the lack of naval control veterans. However, they did not know of any confounding factor which would account for the higher levels of translocations in the veterans.
Who did this research?
This research was performed by a group of researchers from Massey University in New Zealand and the Institute of Cancer in France. The study was largely financed by a grant that the New Zealand Government gave to the New Zealand Nuclear Test Veterans Association.
Donations were also made by the New Zealand Cancer Society, the New Zealand Royal Society, the Lion Foundation Trust, Marlborough Ex-Royal Navalmens Club, New Plymouth RSA, Mt Maunganui RSA, Palmerston North Rotary Club, KJ O’Sullivan Trust, Ruapehu Almoners Association, HMNZS Otago Association, Commodore RT Hale and members of the NZNTVA.
A group of New Zealand nuclear test naval veterans were found to have three times the level of translocations and higher amounts of dicentrics, acentrics and complex rearranged chromosomes compared to a control group.
In the opinion of the researchers, the New Zealand veterans were likely to have been exposed to ionising radiation.
Links to the research paper
This is a peer-reviewed study meaning that other scientists have reviewed this work before the authors published it in the journal Cytogenetic and Genome Research in 2008:
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