Title: Creation of a Quantitative Historical Job-Exposure Matrix for Plutonium Workers and Feasibility of its Use with Reconstructed Occupational Histories for Epidemiological Purposes
Funder: Department of Health (England)

Abstract: The purpose of this proposed study is to establish a useful exposure surrogate which can be validated by plutonium dosimetry measurements and provide a quantitative and meaningful proxy for directly estimated dosimetry to be used in planned future epidemiological studies of the complete Sellafield cohort of over 12,500 workers. The alpha-particle-emitting isotopes of plutonium are of great patho-biological interest because of their heterogeneous distribution in the body and the high biological damage along the short paths of the alpha particles, leading to potential outcomes such as lung cancer (for inhaled material). The public health implications arise both from the relatively large numbers of workers potentially exposed, but also because of analogous exposures (to radon daughters) in the general population. However, epidemiologic study is hampered by serious exposure misclassification, leading to the dilemma of either determining incorrect risk estimates based on a large proportion of inaccurately estimated doses or else the conduct of studies with limited power when restricted to only subjects with accurate dose estimates. This proposal aims to solve this dilemma. It will be an essential first step towards estimating internal radiation dose (research priority D), but will also be important for deriving accurate low dose estimates necessary for research priorities A and C. The study aims to use available accurate urine sample dosimetric data available for a subset of the Sellafield workforce from a measurement programme started soon after the start of the facility in 1951. Using established algorithms these will be used to derive estimates of internal plutonium dose to create a 3-axes (job/task, time and exposure) historical, quantitative Job-Exposure Matrix (JEM) [1,2]. Correlations (that may differ depending on context) between internal plutonium dose and airborne plutonium measurements from the same periods and locations [3,4] will be utilized to complete the JEM. Furthermore, these data will be used to overcome, or minimize, the effect of misclassification in urinary samples prior- (reusable glass) and post- (disposable plastic) 1971 in a more sophisticated way than applying a uniform factor 3 [5]. Subsequently, the JEM will be validated using an a priori withheld random set of the urinary samples. The feasibility of deriving accurate plutonium career-exposure estimates using the JEM for future epidemiological research in this population will be demonstrated by re-creating full occupational histories from a sub-cohort of the workforce (N=578); those with at least one urinary sample taken before 1963. These have been selected because (a) workers have been employed in all sections of the facility, (b) start and duration of employment are expected to be the most challenging in terms of recovering full occupational data, (c) will have urinary samples for pre- and post-1971 periods, and (d) they have been involved in early plutonium operations with relatively high exposures. In addition to occupational histories, information on occupational confounding factors, including asbestos and organic solvents exposure, will be evaluated and where possible collected. Further, the opportunity will be taken to assess the possibility of inaccurate and unrecorded exposures to external sources, in particular to neutrons. The research team consists (University of Manchester, Health Protection Agency and Sellafield Sites Ltd) has longstanding expertise in occupational, environmental, and radiation epidemiology, including exposure estimation and statistics. The potential impact of this work arises mainly from because it will provide the basis for far better risk estimates for the consequences of exposure to (internal) alpha emitters and particularly over protracted periods. This may have implications beyond historically exposed workers i.e. extending to future workers in the industry and to the general population who may be exposed to alpha emitters. Exposure limits may eventually need to be reviewed by the relevant policymakers.


Research activity codes: 4.2 EVALUATION OF MARKERS AND TECHNOLOGIES
Health categories: GENERIC HEALTH RELEVANCE