The committee’s discussion on this topic focused on epidemiological studies that appear to show higher incidences of cancers, including childhood leukaemias, in coastal areas of the UK and near estuaries. The hypothesis to be examined is these higher incidences are linked to inhalation of radioactive particulates originating from effluent discharges to sea from nuclear sites, especially sites where nuclear fuel is or was reprocessed (ie Sellafield and Dounreay). Particulates could be transferred from seawater to land via seaspray. It is also known that radionuclides discharged to sea tend to accumulate in mud banks. Particles from these banks could move back into the water and be washed ashore. It is also possible that when mud banks are uncovered at low tide particles could be blown inland by the wind. The radionuclides of concern include isotopes of plutonium and other alpha emitters. Particulates containing these radionuclides can lead to high radiation doses to very small volumes of body tissues, rather than the low uniform doses to larger volumes of tissues assumed in current models, and it has been suggested that the risks from intakes of such particulates have been underestimated.

The epidemiological work to date has shown clear excesses of childhood leukaemia near Sellafield and Dounreay but findings for other UK coastal nuclear sites are less clear. Some studies have shown increased incidences of cancers but others have not. There are some specific questions about leukaemia incidence around estuaries that the committee will need to return to at a later meeting.

There have been a number of studies of levels of plutonium in people’s bodies that are potentially relevant to the epidemiological findings. Measurements of plutonium concentrations in body tissues made available from autopsies have shown some elevated levels in people living in West Cumbria. Analyses of the ratios of plutonium-239 to plutonium-240 indicated that the source of the plutonium was discharges to air from Sellafield, not sea to land transfer. Measurements of plutonium levels in the urine of children from the Dounreay and Glasgow areas showed that there was no difference between children from the two areas, nor between children who had leukaemia and those who did not.

There have also been measurements of plutonium in children’s teeth (deciduous teeth and those extracted by dentists). These show higher levels in West Cumbria than elsewhere. The committee understands that work is in progress to determine the plutonium-239 to plutonium-240 ratios in these teeth. It is hoped that this will provide information on whether the dominant source of the plutonium is Sellafield discharges to air, Sellafield discharges to sea or weapons test fallout. The committee is contacting the research team involved to obtain details of this work and its preliminary findings.


The government-funded body that collects and analyses health statistics for small areas is the Small Area Health Statistics Unit (SAHSU). This body was set up in 1987, largely to implement a recommendation made in Sir Douglas Black’s report on the possible increased incidence of cancer in West Cumbria. SAHSU maintains a database of post-coded health data, with databases on occupational and environmental exposure to carcinogens and mutagens, carries out research and provides expert advice to government departments and agencies. In recent years there have been criticisms of the way in which SAHSU operates and the methodologies it uses for analyses of data related to radioactivity in the environment. Unresolved differences between SAHSU’s findings and those of NGOs have caused concern and distrust in communities around nuclear installations. Also, NGOs have encountered difficulties in obtaining the small area cancer incidence data from the Cancer Registry that are given to SAHSU.

The committee is considering how research might be carried out in future so as to avoid these problems. The suggestions being examined include one that there should be new studies of areas around one or more nuclear installations. In these studies the hypothesis to be tested and the cancer incidence data to be used would be agreed in advance, and the analysis would be carried out by researchers from a range of organisations, including NGOs. Ways would need to be found to preserve the confidentiality of data for post-code areas so that individuals who have cancer could not be identified when the results are published. The committee will continue to consider the feasibility of these and other studies, with a view to developing specific proposals for future research.


‘Relative biological effectiveness’, RBE, is the term used for the capacities of various types of radiation to lead to biological damage. (For example, the RBE of alpha particles is much greater than that of beta particles.) RBEs are determined from experiments and observations. They are used in specifying the ‘radiation weighting factors’ that form part of the definitions of ‘equivalent dose’ and ‘effective dose’ that are used in radiological protection. RBE values depend on, amongst other factors, the biological endpoint chosen and the dose and dose rate, and most RBEs have been obtained from experiments on rodents or rodent cells. As a result, there are uncertainties in using them.

In discussing the nature and size of uncertainties in RBEs, the committee took the view that it is important to distinguish between two types of situation:

1. those in which general estimates of radiation doses and risks are required (for example, for routine control and planning purposes);
2. those in which detailed estimates of radiation doses and/or risks are required (for example, for use in analyses of epidemiological data).

In the first case broad-brush values of RBE are likely to be sufficient. In the second case it is preferable to use RBE information that is, as far as possible, specific to the energy of the radiation, the radionuclide and the tissues or cells of interest.

ICRP is concerned primarily with the first type of situation. CERRIE has learnt that an ICRP report on relationships between RBE and radiation weighting factors will be published for consultation in late 2002 or early 2003. CERRIE will consider this ICRP report when it is issued. It is not yet clear to the committee whether ICRP will offer advice for the second type of situation. There appears to be a particular need to address RBEs for low energy photons and electrons, high energy photons and Auger emitters, taking into account microdosimetric information and quantifying both variability and uncertainty.


The committee discussed second event theory at both its fourth and fifth meetings but, for simplicity, the discussions are reported together here. Low LET radiation (beta particles and gamma rays) and high LET radiation (alpha particles) were considered separately.


As reported in the summary of the third meeting [insert link], published calculations give different estimates of the factor by which the damage from strontium-90/yttrium-90 is predicted by the second event theory to be greater than that caused by the same dose of external gamma radiation. The committee has ascertained the reason for this difference: it is in the assumptions made about the volume of space occupied by cells and the location of the strontium within the space. The conclusion reached is that the calculations that indicate that 30 times more damage from strontium-90/yttrium-90 than from gamma radiation do not support the second event theory as currently formulated. Also, the theory predicts that the number of double events from gamma radiation would increase with the square of the dose, but the committee has not identified any evidence to indicate that this prediction is true. This is not to say that second events are unimportant. It could be that a reformulated version of the theory is substantially correct.


Calculations carried out for the committee showed that small plutonium particles (0.5 microns) could be a factor of about 15 more likely to cause second events than the ICRP models based on uniform exposure predict, but this is only the case if cell killing is ignored. If the capability of the alpha-emitting plutonium particles to kill cells near to them is taken into account and the cells are not replaced, the ICRP approach predicts greater hazard for the uniform exposure than the particles. The question to be answered is thus the extent to which cell killing and replacement is observed.


The committee has commissioned a review of the existing literature to find out whether there is biological evidence that sheds light on the importance or otherwise of second events. Members will also examine existing mouse tissue data for evidence of local cell killing and fibrosis by plutonium particles.

Next (Meeting 6)