Wakeford blames extreme cluster on population mixing
Full copy of Richard Wakeford's essay in Journal of Radiological Protection
blaming population mixing for Fallon leukaemia cluster
News and information
Extreme childhood leukaemia cluster at Fallon, Nevada
When, in 1983, Yorkshire Television announced its discovery of a pronounced excess of cases of childhood leukaemia in the coastal village of Seascale, adjacent to the Sellafield nuclear complex (formerlyWindscale and CalderWorks) in Cumbria, there was considerable concern that the current system of radiological protection may be seriously deficient. The Black Advisory Group was immediately established to investigate the ten cases in the village over thirty years, and a whole raft of scientific studies was launched. This concern also led to the creation of the UK Government’s independent expert advisory Committee on Medical Aspects of Radiation in the Environment(COMARE)in 1985. That comprehensive assessments carried out by the National Radiological Protection Board could not begin to account for the excess cases in terms of radiation exposure due to radioactive discharges from Sellafield was taken by some as an indication that substantial and fundamental flaws underlie the radiation risk models derived by authoritative bodies such as the International Commission on Radiological Protection. Concern was heightened in 1986 when an excess of childhood leukaemia was reported as having occurred around the Dounreay nuclear establishment in northern Scotland, particularly in the town of Thurso. There followed a number of reports (of varying quality) of raised levels of childhood leukaemia near certain other nuclear installations, but, as at Sellafield, radiological assessments found that radiation exposures were substantially less than would be required to explain the excess cases. Scientific investigations have failed to find errors in these assessments that would be large enough to infer that radiation exposure was the cause of the extra cases. The idea that the risk from radioactive material in discharges, such as plutonium and fission products, might have been grossly underestimated seemed unlikely when studies of the effect of fallout from atmospheric nuclear weapons testing did not find an unexpectedly large rise in childhood leukaemia, and what initially appeared to be an important finding of a statistical association with occupational irradiation of fathers before the conception of their children was not confirmed by subsequent studies.
Despite the failure of scientific investigations to find serious shortcomings in the radiological assessments, many have been reluctant to dismiss radiation as playing a role in the excesses of childhood leukaemia, particularly in the cluster of cases at Seascale. It just seemed that this role must be a complex one that remains to be understood. Indeed, in the absence of an alternative explanation, this position has its attractions. However, in 1988, Professor Leo Kinlen proposed that childhood leukaemia is a rare response to a common, but unidentified, infection. When substantial numbers of infected and susceptible individuals come into contact, as when urban and rural populations mix, localised epidemics of the infection can occur giving rise to additional cases of the rare response, childhood leukaemia. The areas around Sellafield and Dounreay are certainly isolated and remote, and have experienced influxes of large numbers of ‘outsiders’; but it was the confirmation by Kinlen and his colleagues of significant excesses of childhood leukaemia in each recent instance of large-scale population mixing in Britain that provided the most striking support for this hypothesis (see Kinlen 2000 Radiol. Prot. Bull. 226 9–18). This evidence is supported by the findings of studies carried out in other countries, most recently by those conducted around La Hague in France (Boutou et al 2002 Br. J. Cancer 87 740–5) and in isolated rural counties of the USA (Wartenberg et al 2004 Br. J. Cancer 90 1771–6). The evidence for an infective process underlying childhood leukaemia is compelling.
Now, a remarkable observation of an exceptional cluster of childhood leukaemia in the USA may lend further weight to the idea that population mixing increases the risk of childhood leukaemia. In remote and sparsely-populated Churchill County, Nevada, 11 cases of childhood leukaemia occurred during 1999–2001 when less than one case would be expected (Steinmaus et al 2004 Environ. Health Perspect. 112 766–71). The nominal Poisson probability associated with this excess (p = 4.3 × 10-9) makes this cluster the most extreme ever to have been observed anywhere in the world by a considerable margin—a cluster this extreme would only occur by chance in the USA once in every 22,000 years! The extreme rarity of the cluster would be even greater were attention confined to the small town of Fallon, where many of the cases occurred. Of special interest to the population mixing hypothesis is the nearby Fallon military airbase, which, since the mid-1990s, has specialised in training. In 2000, a staggering 55,000 persons attended Fallon airbase for training, coming from many parts of the world. Given the background evidence for the impact of population mixing upon the risk of childhood leukaemia, the large numbers of people of diverse origins passing through the Fallon airbase is an attractive explanation for the childhood leukaemia cluster in its highly rural vicinity.
So, the childhood leukaemia cluster at Seascale may not be attributable to radiation, as initially might have seemed, and the radiological protection community was right to stand its ground. Nonetheless, much good scientific work has been conducted on the basis of the concern about a possible shortcoming in radiation risk assessments, and radiological protection is the stronger for it. But what a contrast between the publicity given to Seascale, next door to a nuclear installation, and that given to Fallon. I suspect that not many reading this will have heard of the Fallon cluster, but all will have heard of the one at Seascale. No doubt this disproportionate media, and consequent public, interest in a possible link between the Seascale cluster and operations at Sellafield has led to a similarly disproportionate level of funding to investigate radiation at the expense of other possible causes. Could be that the money was put on the wrong horse.
Richard Wakeford
J. Radiol. Prot. 24 (2004) 183–188 www.iop.org/Journals/jr
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