It will come as no surprise that a ‘precautionary approach’ should be taken to internal radiation. That was the recent conclusion of the Committee Examining Radiation Risks of Internal Emitters (CERRIE), a body set up under the wing of the UK’s Committee on Medical Aspects of Radiation in the Environment (COMARE), an independent group that advises government on such matters.

What may be surprising is the scope of the uncertainty in our knowledge. The CERRIE report states that although current thinking on risks is not substantially wrong, uncertainties about the risks mean that in some cases we might be exposed to ten times the risk previously thought, while in other cases the risk may be almost zero.

More surprising still is the controversy that the outcome of the CERRIE report has been mired in. Disagreements between the committee members escalated to the point that the drafting of the final report almost descended to a fist fight. Two members decided they could not be associated with the majority view and even went as far as publishing a CERRIE Minority Report and claiming that the “nuclear project cannot function without freedom to dump and pollute.”

UNCERTAINTY

On the main business of dose and risk estimates, the committee’s opinion was that insufficient attention had been paid in the past to uncertainties for internal emitters. Indeed, reliable estimates of uncertainties in dose coefficients for a range of radionuclides were not yet available.

Uncertainties in estimating equivalent dose were significant and varied in magnitude from factors of two in the most favourable case to more than ten in the least favourable, above and below the central estimate. This would depend on factors such as the type of radionuclide, its chemical form, the mode of exposure and the body organ under consideration. Thus, under some circumstances the equivalent dose may be substantially greater, or substantially smaller, than current best estimates.

For effective doses, there were additional uncertainties in the use of tissue weighting factors. Further work was required to quantify uncertainties in dose estimates for important radionuclides, with transparent identification of all the underlying contributions to overall uncertainties and how to compound them. The committee concluded that dose and risk estimates should contain an explicit indication of the uncertainties involved. This approach would help identify those situations in which a precautionary approach was appropriate, which was preferred to the use of conservative assumptions in models.

Current models used for dose and risk estimation are particularly limited in their treatment of radionuclides that emit very short-ranged particles, causing inhomogeneities of dose within tissue on a microscopic scale. These include alpha emitters, low-energy beta emitters and Auger electron emitters.

NOVEL EFFECTS

CERRIE also considered a number of novel aspects of radiation biology that had emerged since the International Commission on Radiological Protection (ICRP) made its 1990 recommendations, which currently form the basis for radiation protection in the UK. These aspects include: induced genomic instability (whereby radiation can induce an ongoing long-term increase in mutation rate in cells and their progeny, which may contribute towards cancer), bystander effects (whereby unhit cells in the vicinity of cells that have been hit by radiation may also be affected by the radiation), and minisatellite mutation induction in the germline (which leads to inherited DNA changes that may have health effects). The committee agreed that these were real biological phenomena, which could in principle have implications for assessments of radiation risk. CERRIE members’ views on the likely implications of these effects differed, but the committee agreed that these differences were primarily due to lack of firm information at present. The effects could in principle lead to underestimation, or overestimation, of risk at low doses under some circumstances.

Almost half the committee was of the view that the biological evidence on these mechanisms was not adequately reflected in current ICRP models. Current risks could therefore be underestimated at least to some degree, and perhaps significantly for some nuclides. Of the remainder of members, some were inclined to the view that risks were adequately taken into account in current models and epidemiological observations. These differences of view existed because of current lack of knowledge, particularly for these effects at low doses of radiation in in vivo situations. The committee were agreed that new findings on novel effects should be included in consideration of health risks at low doses and their quantitative uncertainties.

Almost half the committee considered that the biological evidence on these new effects had immediate implications for radiological protection standards and that government should consider the precautionary principle, while others supportive in general of the precautionary principle, did not agree because they perceived a current lack of coherence in the experimental data and an absence of clear links with health effects.

A few months before publication, CERRIE’s final report was leaked to New Scientist magazine which ran a news story explaining that “risk from exposure inside the body could be ten times higher than is allowed for in calculating international safety limits.” CERRIE members Richard Bramhall of the UK Low-Level Radiation Campaign and Chris Busby of the Green Audit wrote a letter in response saying that was a “massive understatement” and the “notorious” leukaemia cluster around the English village of Seascale, near Sellafield, has “no credible alternative explanation other than that radiation” from the plant was the cause. Amazingly, their letter cited their membership and was published in September 2004, over a month before the final report itself.

TROUBLESOME MEMBERSHIP

CERRIE was established in 2001 following concerns about the health risks of internal radiation, including reports of increased incidences of cancer near nuclear sites and after the Chernobyl accident by the then environment minister Michael Meacher. In line with draft government policy, Meacher specified that the committee membership should be widely representative and contain members with a range of views, some of which may not be represented on other committees. The nuclear power industry was represented alongside scientists associated with environmental groups, the National Radiological Protection Board and independent academics.

The remit of CERRIE was “to consider present risk models for radiation and health that apply to exposure to radiation from internal radionuclides in the light of recent studies and to identify any further research that may be needed.” Implicit in that remit was the expectation that it would examine a number of hypotheses proposed over the past decade by two members of the committee: Bramhall and Busby.

A COMARE statement on CERRIE expresses “reservations about how the committee was set up, particularly how its composition was influenced by a minister rather than under the guidance of the Office of the Commissioner of Public Appointments.”

With thinly-veiled frustration, CERRIE’s press briefing states that much of the committee’s time and effort was spent examining these theories in considerable detail. These theories included hot particle theory, biphasic dose responses, and the theory that differences exist between man-made and natural radionuclides as classes. The most interesting, however, was the second event theory (SET) described by Busby in his 1996 work, Wings of Death. The SET is based on the assumption that during 90Sr-90Y decay the first beta particle serves to create a sub-population of radiosensitive cells. A subsequent hit from the second 90Sr-90Y decay series during this time window would then provide for extremely high mutational response.

In order to explore more fully the biological plausibility of the SET, the committee commissioned an external review of experimental data from Barrie Lambert, a radiation expert from St Bartholomew’s Hospital, London. The review concluded that it is not possible to totally exclude unexpectedly increased radiobiological effects attributable to the SET, but that the bulk of evidence tends to argue against this proposition.

The committee, apart from Bramhall and Busby, considered that none of these theories were supported by the available scientific evidence. The final report even goes as far as to say that the evidence substantially contradicted the SET. The CERRIE report cites a lack of biological plausibility for the basic preconditions of the SET; a lack of supporting evidence in the proponents’ reviews of the SET; weakness in the few studies cited in support of the SET; and the Lambert review as its grounds for rejection.

EPIDEMIOLOGICAL EVIDENCE

A number of epidemiological studies that had been put forward as definitive evidence of inadequacy of predictions of risk from ICRP models were considered. Further analyses were also carried out on the incidence of infant leukaemia in Great Britain after the Chernobyl accident, and on trends in childhood leukaemia incidence in Great Britain to include the period after radioactive fallout from atmospheric nuclear weapons testing in the northern hemisphere.

The analysis found no indication at all of any increase in childhood leukaemia in Britain associated with weapons fallout. Whilst its other study produced results that are generally in the direction expected from Chernobyl contamination increasing the risk of infant leukaemia, the increase is not statistically significant; numbers of cases are so small that the findings cannot exclude the possibility of there being no increase in risk at all.

The committee agreed with the standard view that epidemiological evidence is compelling for there being a raised risk of adverse health effects in those exposed to moderate and high levels of internally incorporated radionuclides. For low-level intake of radionuclides, all but one member of the committee accepted that there was probably some increased risk of adverse health effects as a result of the internal irradiation of organs and tissues, although this increase may be undetectably small.

The report states that “only two CERRIE members” thought that current models underestimate epidemiological risks from intakes of radionuclides by very large factors, the rest considered such possible errors to be modest or not even shown by the evidence.

Some studies that showed a correlation between incidence of childhood leukaemia and proximity to a nuclear installation were discounted because they had not been published in scientific journals or peer reviews. Unsurprisingly, some of these were authored by Busby and this proved to be a significant source of controversy: there were “differences of view” about the appropriateness of the data and methodologies used in epidemiological studies and from different interpretations of the findings.

A core methodological limitation of many of the epidemiological studies was their reduced statistical power at low levels of exposure and risk. In addition, the use of some reports was hindered by a lack of scientific method and error checking. Peer review was considered essential.

The “two members” thought that radionuclides disposed of at sea during reprocessing activities could make their way back to land by a variety of natural means and go on to cause cancers.

About half the committee pointed to other leukaemia clusters away from nuclear sites and to nuclear sites where there were no clusters. They believed a possible explanation was the hypothesis of population mixing which supposes that child leukaemia is a response to an as-yet unknown infection to which rural populations are more susceptible. The hypothesis has been tested at many nuclear sites (Burghfield, Dounreay, La Hague) as well as other non-nuclear rural construction sites where similar mixing has occurred, and other circumstances such as the evacuation of children during wartime. Although CERRIE did not specifically address the hypothesis, COMARE’s 2002 report stated: “The currently available evidence indicates that population mixing is responsible for a substantial part of the excess of leukaemia and non-Hodgkin’s lymphoma among young people in Seascale. There is strong circumstantial evidence for the involvement of infectious agents in the population mixing effect, although the biological mechanism is not yet clear.”

MINORITY REPORT

When it came to drafting the final report, committee members found that it was very difficult to agree a wording to express all their views. Bramhall and Busby requested that a dissenting statement be included in the report – and the committee as a whole agreed. Sadly, over a period of three months, negotiations on the wording of the statement deteriorated to a shouting match where the dissenters told the committee they must accept their latest draft or nothing. The Times reported that lawyers acting for the UK government’s Department for Environment, Food and Rural Affairs (Defra) sent letters to all 12 committee members warning them that they could be sued for defamation if they included the statement in the final report.

The report states:

In the end, the committee decided not to include in its report any of the draft versions of a dissenting statement for a number of reasons. First, the drafts did not adequately identify the reasons for the disagreement with the committee’s report. In addition, the committee’s members, as scientists, had a professional duty not to be party to the publication of incorrect statements of fact. Furthermore, some members were reluctant to expose their employers to vicarious legal liability for their actions if the committee were to publish the dissenting statement as it stood.

The dissenting members stated their wish that it be recorded that the committee’s report did not adequately reflect their views. The dissenting members said that they would not endorse the committee’s report.

In addition to Bramhall’s and Busby’s dissent, a member of the committee secretariat, Marion Hill, resigned over the matter. In her resignation letter she alleged that the committee chairman, Dudley Goodhead, and another secretariat member, Ian Fairlie, were excluding her from work processes and that this has serious consequences in terms of bias. Hill’s letter was included in the Minority Report, which claimed a rather different different remit for the committee: “To identify areas where consensus could not be reached, to explain the reasons for any areas of disagreement and suggest ways to resolve them.”

Meacher, speaking at the launch of the Minority Report, for which he wrote an introduction, said he would write to the current environment minister, Elliot Morley, for an explanation of the dissenters’ exclusion from the official report which he said did not “accommodate a full and fair representation of all views.” He added: “It is very worrying, for it is hard to conjecture that if the child leukaemia peak in Europe was real, anything other that radiation from Chernobyl could have caused it.” He said that the idea of CERRIE had been “to examine all the questions, and where there was disagreement to recommend further research. It is criminally irresponsible not to allow all the evidence to come out so there can be a properly organised public debate.”

At the launch of the official report, the chair of the committee, Dudley Goodhead, said: “The report examines the views of all members, including hypotheses for very large risks put forward by two members, who finally dissented from the report. The committee concluded that the available scientific evidence did not support these hypotheses and, in many cases, substantially contradicted them.” He continued: “Apart from these two members, there was an encouraging degree of consensus among the remaining ten members who included representatives from the NRPB, the nuclear industry, environmental groups and scientists with strongly independent views.”