Scenario 

     Sellafield nuclear processing plant, on the Cumbrian coast in UK, was constructed in 1942 and commenced in September 1947, originally for the production of weapon grade plutonium, and later operating as a decommission and reprocessing plant which separate uranium, plutonium and fission products from spent nuclear fuel from commercial reactors.

     The workers are potentially at risk for the exposure to radiation either externally from the radioactive wastes (mostly gamma-rays) or internally by inhalation of radioisotopes (mostly plutonium). The external dose has been monitored by dosimeters (e.g., film badge) for workers in area of the plant in which radioactive materials were present. The uptake of plutonium was estimated principally in urine samples. For the plutonium, there are two ways of exposure; one is alpha-emitting isotopes (^238/239/240Pu, in which ²³⁹Pu is a major component) and anther is ²⁴¹Pu which decays by beta particle emission to the alpha-emitting ²⁴¹Am.

     For example, the followings are the annual levels of (A) average external radiation and (B) average uptake of plutonium studied for cancer risk in over 14,000 workers employed during 1947-1975. Among all radiation workers, approximately 50% are plutonium workers, in which 89% have been assessed for plutonium dose. ([A], Douglas, A. J. et al., Br. J. Cancer, 70:1232-1243, 1994; [B], Omar, R. Z. et al., Br. J. Cancer, 79:1288-1301, 1999).

Blood samples were obtained from 54 plutonium workers. According to the plutonium body burden as measured by urine analysis, they were divided into three groups. Lymphocyte chromosome aberrations were analyzed by G-banding method. As a result, it was suggested that significant deposition of plutonium do cause an increase in chromosome aberrations. 

Tawn, E. J., Hall, J. W. and Schofield, G. B. (1985): Chromosome studies in plutonium workers. Int. J. Radiat. Biol., 47:599-610. 

Chromosome aberration analysis 

      Chromosome aberration analysis in peripheral blood lymphocytes was carried out using G-banding method. Two groups of plutonium workers were selected depending on their plutonium levels; one with 20-50% maximum permissible body burden (MPBB) and another with higher than 50% MPBB. Each group was compared with age-matched workers with comparable level of external dose alone (external dose controls) and workers with neither plutonium nor external dose (unexposed controls). Blood samples were obtained between February 1988 and October 1991 (except for one case sampled in 1986).
     Significant elevation of translocations was found for plutonium workers and external dose controls as compared with the unexposed controls. 

Whitehouse, C. A., Tawn, E. J. and Riddell, A. E. (1998): Chromosome aberrations in radiation workers with internal deposits of plutonium. Radiat. Res., 150:459-468. 

Observations: Significant elevation of translocations was found for plutonium workers and external dose controls as compared with the unexposed controls. 

     Tawn, E. J. and Whitehouse, C. A. (2005): Chromosome intra- and inter-exchanges determined by G-banding in radiation workers with in vivo exposure to plutonium. J. Radiat. Prot., 25:83-88.
     Whitehouse, C. A. and Tawn, E. J. (2001): No evidence for chromosomal instability in radiation workers with in vivo exposure to plutonium. Radiat. Res., 156:467-475. 

     Chromosome aberration analysis was carried out by FISH method on the retired male workers (Ex-workers) from Sellafield nuclear processing facility. Chromosome aberrations in peripheral blood lymphocytes were carried out by FISH-painting technology using whole chromosome painting probes fro chromosomes 1, 3 and 4.

    [1] External exposure: In the first set of study (ref. 1), a total of 294 Ex-workers were categorized into 3 groups according to their lifetime occupational external doses as measured by film badge reading. They were a high-dose group with >500 mSv, an intermediate-dose group with 200-350 mSv and a control group with <50 mSv. In this study (i.e., examination of the effects of low-LET external occupational radiation exposure), any individuals with known histories of substantial intake of radionuclides or who had received radiotherapy were excluded. All samples were obtained between February 1997 and February 2000.

     [2] Pu internal exposure: In the second set of study (ref. 2), 46 retired plutonium workers (Pu Ex-workers) were selected from the male Ex-workers with assessed internal bone marrow doses over 60 mSv. The included 34 workers having robust RBM dosimetry and 12 workers whose internal doses were less reliable. For comparison, age-matched 34 workers with similar recorded external doses but negligible internal dose for externa dose controls, and 34 workers with negligible radiation exposure for unexposed controls.  

     (1) Tawn, E. J., Whitehouse, C. A. and Tarone, R. E. (2004): FISH chromosome aberration analysis on retired radiation workers from the Sellafield nuclear facility. Radiat. Res., 162:249-256.
     (2) Tawn, E. J., Whitehouse, C. A. and Riddell, A. E. (2006): FISH chromosome analysis of plutonium workers from the Sellafield nuclear facility. Radiat. Res., 165:592-597.