No definitive evidence to support leukaemia cluster claims
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SIR – The article entitled “No leukaemia cluster... that’s just not true!” by Corrina Thomson in last week’s John O’Groat Journal leaves the reader with the distinct impression radioactive discharges and pollution from Dounreay may have contributed to the reported childhood leukaemia cluster in the surrounding area.
While a few may subscribe to this notion, a massive body of scientific evidence suggests otherwise. Indeed, there is a strong probability the observed leukaemia cluster has no relationship, whatsoever, to any operational activity conducted at the facility.
Ms Thomson begins the article by noting the 14th report of the Committee on Medical Aspects of Radiation in the Environment (COMARE) in which it is concluded no evidence exists of an increased risk of leukaemia in under-fives living around UK nuclear plants in the 35-year period between 1969 and 2004.
She adds this study was prompted, in part, by a 2008 German study (KiKK) which reported children are more likely to contract leukaemia the closer they live to a nuclear plant. She further notes the KiKK study and its scientific method were investigated by two German government oversight agencies, one of which published a final assessment of the KiKK report in which it stated: “The central finding of the [KiKK] study on childhood cancer in the vicinity of nuclear power plants is... confirmed.”
Ms Thomson goes on to question why only power reactors (which produce electricity) were included in the COMARE study and not experimental or reprocessing sites such as Calder Hall, Sellafield, Winfrith, Dounreay, etc, and adds, “...there is one very good reason why the excluded nuclear plants should be included and the sites studied as a whole – the elevated cancer data is highly relevant if new power plants are to be located at these excluded sites. The discharges from a new power reactor at Sellafield, for example, will be cumulative in the environment with the existing discharges and pollution from reprocessing.”
Here then, is the implied association between leukaemia clusters on the one hand and “discharges and pollution” on the other. Unfortunately, some critical research findings that bear directly on the issue of leukaemia clusters in the vicinity of nuclear plants, and which might have been used to provide a more balanced perspective, is entirely missing from Ms Thomson’s article.
The following are a few germane points:
1: The Dounreay cluster was first reported in 1986 in a study commissioned by the Scottish health services which looked at the incidence of leukaemia among individuals aged 0-24 years living within 25 kilometres of Dounreay during a 17-year period from 1968 to 1984. Six cases of leukaemia were observed compared with the three expected on the basis of Scottish national averages.
All six cases occurred between 1979 and 1984 and most were centred on the west side of Thurso where the majority of newcomers to the community resided. A key point here is the numbers are very small and reflect observations conducted over an extended time period. Although the difference between the observed and expected cases qualifies as a cluster from a scientific point of view, such small numbers accumulated over such a lengthy period are not what most people understand by the term “cluster”.
2: No definitive scientific evidence has ever been presented that any nuclear plant or reprocessing facility in the world, operating under normal conditions, has caused a single cancer in any person – of any age. With the exception of the 1986 Chernobyl accident, the same is true for power plants that have occasionally operated under abnormal conditions.
3: The KiKK study makes no claim of any relationship between environmental radioactivity and the reported increased incidence of childhood leukaemia. To the contrary, the KiKK and German government reports explicitly state the findings do not allow the conclusion radiation emitted from nuclear reactors is the cause.
4: Several scientific bodies, including COMARE, have noted shortcomings in the KiKK design including the use of distance from a power plant as a substitute for measured radiation levels, problems in selecting appropriate controls, the failure to take account of residential histories, and the absence of possible confounding factors such as population mixing from the published report – all of which reduce confidence in the findings.
5: Consistent with the 14th COMARE report, most studies conducted in other nations have found no increase in the incidence of childhood leukaemia around nuclear plants.
6: A previous COMARE study (fourth report, 1996) focused on childhood leukaemia in the Sellafield area and concluded “on current knowledge, environmental radiation exposure from authorised or unplanned releases could not account for the excess” (of leukaemia and non-Hodgkin’s lymphoma). Both the Sellafield and Dounreay facilities are the subject of ongoing studies by COMARE.
7: Many types of childhood cancers occur in clusters rather than in a random fashion. Such clustering occurs at all population levels throughout the world, down to local levels.
8: Both in Germany and the UK, an increased incidence of childhood leukaemia has been observed in areas where nuclear plants had been planned but not yet built, and the magnitude of the increases is similar to that reported in the vicinities of several operating plants.
9: Studies of leukaemia clustering near nuclear stations command widespread media attention but clustering in non-nuclear areas go largely unnoticed. For example, epidemiologists at Newcastle University located five clusters in the North of England, one around Sellafield and four at locations remote from nuclear installations. The latter are seldom mentioned.
10: Several follow-up studies of the Chernobyl nuclear accident in 1986, in which many areas of Europe, the Ukraine and Russia were heavily contaminated with radioactive fallout, showed no convincing evidence of an increased incidence of leukaemia in children under five years who were exposed after birth. Two other reports suggested a minor effect for children yet unborn but this was not confirmed in three separate studies.
11: A large and ever-increasing body of medical evidence suggests leukaemia clustering in young children in rural areas arises from the mixing of a historically stable local population with a high diversity of incomers from urban areas.
The hypothesis is that such population mixing sometimes sets the stage for unusual patterns of infectious disease which marginally increases the risk of acute leukaemia. Other related hypotheses, such as the lack of childhood immunity to infectious agents, have been advanced.
((BLOB)) In addition to Dounreay incomers, population mixing in the Thurso area has been associated with North Sea oil exploration.
One study concluded the increased incidence of leukaemia observed during the 1979-1984 period in and around Thurso is most likely due to intense population mixing among oil workers employed away from home in a community where the proportion of such workers was previously low.
((BLOB)) A recent Oxford University study has confirmed marked population mixing in 12 studies in six different countries in which an increased incidence of childhood leukaemia was observed in a non-nuclear setting, as well as four of five cases (including the Dounreay
While clusters of leukaemia and other childhood malignancies are prevalent throughout the world, and are occasionally observed in the vicinity of nuclear power plants, conclusive evidence of an underlying cause is invariably lacking.
Indeed, childhood leukaemia is not a single disease but rather a group of closely related diseases, each with a unique and complex pattern of genetic abnormalities, and it would be unreasonable to expect a simple and universal triggering mechanism such as ionizing radiation.
Although interesting theories abound, the fact remains no definitive evidence exists at the present time to support any relationship between childhood leukaemia and radiation exposure at Dounreay or, indeed, at any nuclear power reactor or reprocessing facility operating under normal conditions anywhere in the world.
The good news is steady progress has been made in the treatment of acute lymphocytic leukaemia in children and the disease is now 90 per cent curable.
David Farquhar,
Professor of cancer research,
University of Texas,
Houston,
Texas, USA.
