The mortality and cancer morbidity experience of employees at theChapelcross plant of British Nuclear Fuels plc, 1955-95

Abstract

The results presented here are from the follow-up of the cohort of workersever employed at the Chapelcross site of British Nuclear Fuels plc (BNFL)between 1955 and 1995. The study cohort consists of 2628 workers, 2249 of whomwere male, who were first employed at the plant before 1 January 1996, and whohave 63 967 person-years of follow-up. The mean follow-up period is24.3 years. The 2209 members of the cohort (84%) classified as radiationworkers accumulated 185.1 person-sieverts of external radiation; their mediancumulative dose was 39.1 mSv, and 95% of their cumulative doses were lessthan 339.3 mSv. The Chapelcross workers show the usual `healthy worker'effect. To the end of 1995, there were 528 deaths among the total cohort(20%), including 449 (20%) amongst the radiation workers. When the dose wasunlagged, a statistically significant association was noted between cancerregistrations of the buccal cavity and pharynx and dose, based on five cases.When the dose was lagged by 10 years, a statistically significant excessrelative risk was noted between all cancer morbidity and dose, 1.80 Sv-1 (0.03 to 4.45), based on 162 cases. This result is driven by thenon-significant, but high excess relative risk estimates from the 12 prostaticcancer registrations. A statistically significant association is noted betweenthe eight deaths amongst radiation workers who had prostatic cancer as theunderlying cause of mortality and cumulative external radiation dose when thedose was lagged by 0, 2 and 10 years. The association is unlikely to becausal. The finding has little biological plausibility as the strength of theassociation weakened as the dose lagging increased; it was strongest when thedose was unlagged and disappeared when the dose was lagged by 20 years. Noneof the workers who was registered for or died from prostatic cancer had everbeen monitored for exposure to tritium or to 51Cr, 59Fe,60Co or 65Zn. There is no evidence to date amongst theChapelcross cohort of increased risk for cancers considered to be radiogenicbased on studies of populations exposed to high levels of radiation.