Radioactivity, most importantly I, Cs and Po, was carried to the East by prevailing westerly winds, though the wind speed and direction varied during the course of the accident.1,2 Deposition to the ground across Northern England ‘‘was dominated by 131I (half-life of 8.04 days) with deposits above 4 kBq m~2 extending about 75 km east northeast and 140 km south southeast of the site, covering an area of about 12000 km2’’ (Jones2 citing Chamberlain).3 Iodine-131 was measured across the North Sea in Holland and Belgium, though concentrations were much lower than in England. Figure 1 shows a map of the iodine release. A recent re-analysis of air monitoring data in Norway4 showed that the radioactive plume reached Norway on the 15th and 16th October. These authors noted that maximum observed deposition was comparable to the level of deposition from atmospheric nuclear weapons testing in 1958. It has been estimated by Garland and Wakeford1 that no more than 10% of the total 131I passed across the East coast of England to the North Sea and Europe.

As the accident progressed, in the early hours of October 11th, the regional police chief constable was notified.5,6 A review of the accident6 concluded that, after the uncertainty and confusion of the initial incident, the aftermath was handled well: ‘‘community warnings and communications were handled efficiently and promptly, environmental survey teams and equipment were assembled and dispatched promptly, and there was an atmosphere of quiet professionalism’’.

Assessment of external radiation doses showed that these were not high enough to require evacuation (Jackson and Jones7 citing Dunster et al.8), but

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Figure 1 Time integrated concentrations of 131I in air following the Windscale acci­dent up to 12.00 on the 15th of October 1957. (Reprinted from Johnson et al. with kind permission of Elsevier).

high levels of radioactivity (principally 131I) in milk implied potentially significant ingestion doses. The majority of iodine ingested by the body is accu­mulated in the thyroid, so radioactive iodine intake results in a risk of thyroid cancer. At the time, no intervention level for 131I in milk had been set, so, in the words of Jones2 ‘‘hasty, but effective, consultations and calculations” determined a maximum permissible level of 0.1 pCi l 1 (3700 Bq l 1). A sampling campaign was set up to determine levels of radioactivity in milk across a large area of the UK. In the local area on the 11th and 12th of October, observed 131I activity concentrations in milk reached 30000Bq l 1, but rapidly declined over the
following weeks. Similar maximum activity concentrations were observed in other foodstuffs.7 Levels in public drinking water sources were not expected to be high.

Approximately three million litres of milk were discarded over an area of around 500 km2 (ref. 7). Restrictions were finally lifted on the 23rd of November, approximately six weeks after the accident.2 It is probable that, at present day intervention levels, the area in which milk consumption was banned would have been much greater7 and temporary precautionary bans on food­stuffs, including meat and milk, would also have been implemented as a consequence of radiocaesium contamination.7,9