COMARE Statement on Benbecula

 

Cobalt-60 has been used to assess the performance of missiles tested at the Royal Artillery Range near Benbecula in the Western Isles of Scotland. Missiles were fired out to sea and a Radioactive Miss Distance Indicator (RAMDI) showed how closely they approached the target. Authorisation for the use of RAMDIs was given in 1967; their use commenced about 1970 and terminated in 1981. MoD estimates that about 5600 missiles were fired, each of which had about 1.85 GBq or 640 MBq of Cobalt-60. The lower activity was used in the later stages of the testing, but the date when it was introduced is uncertain. Most of the activity reached the sea, but some leaked before the missiles were fired.

MoD has asked COMARE to make a statement on the likelihood of any health effects resulting from the use of cobalt-60 on the Benbecula range and to advise on whether any further work is required.

Three studies of cancer incidence in the Benbecula area were undertaken in the 1990s by the Scottish Information and Statistics Division (ISD). It is understood that these studies were stimulated by Chernobyl, or general concerns about cancer levels in the area. These studies involve small populations and the statistical uncertainties are inevitably substantial. Nevertheless, there was no strong suggestion of any increase in cancers overall or of any of the sub-groupings considered over the period of the study. Indeed, cancer incidence in the Western Isles is somewhat lower than in Scotland as a whole.

Very recently (August 2004), COMARE was notified of a new study which examined the incidence of all malignant neoplasms (taken together) for the period 1975 to 2001 (all years combined). The study considers cancer incidence in males and females in all of the ten postcodes comprising the Western Isles. Comparisons are made with the Western Isles as a whole. None of the standardised incidence ratios was significantly elevated.

COMARE believes that the methodology of the studies carried out by ISD is appropriate, given the constraints on such small area studies.

Cobalt-60 has a physical half-life of about five years. If released into the environment, much of the dose to people is typically delivered by external radiation, but some activity may be ingested or inhaled. If it is taken up into the body it will irradiate body organs until it decays away or is excreted. Doses are reasonably uniform across the body; about 70% of the dose is delivered in the first year and doses are about 95% complete within five years of intake. It is likely that the doses from the Benbecula releases must have been substantially complete by the mid 1980s with a peak five or ten years earlier.

COMARE is not aware of any evidence suggesting that the local population received significant doses from the cobalt releases in the Benbecula area. Nor do the completed epidemiological studies suggest that there are elevated levels of cancer. COMARE does not believe that there is any reason to think that the health of the local population has suffered perceptibly as a result of these releases. Nevertheless, despite the problems of small numbers, it would be sensible to continue epidemiological monitoring for another few years in order to be quite sure that no late excess of cancers emerges. It would also be sensible to update the most recent analysis for broad sub-groups of malignancies, perhaps for all postcodes combined, so as to combat problems of small numbers and multiple significance testing.

As long as the site remains secure, there is no need for further environmental monitoring.



17 January 2005

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