Workers exposed to asbestos may encounter radiation as radon or from other sources. Both asbestos and radiation are etiologic agents in pulmonary fibrosis. The aim of this study is to determine whether concomitant radiation exposure in asbestos workers increases the incidence of pulmonary fibrosis.
2263 asbestos exposed former nuclear weapons workers from a medical surveillance program form the study cohort. PA chest radiographs and spirometry were performed for screening. Fibrosis was defined by B-read opacity profusion category on chest radiographs > 1/0, or spirometric evidence of restrictive or mixed disease. The cohort is largely male (91.0%) with an average age of 63.3 years. 1157 workers had complete work histories, including external radiation badge doses and laboratory data.
The demographic and fibrosis endpoints were similar in the entire cohort vs. the 1157 analyzed. Asbestos exposure based upon years in a potentially exposed job was divided into low (< 13 years) and high ( >13 years) dose groups. 31 (5.4%) of the high dose vs.24 ( 4.1%) of the low dose group had ILO scores > 1/0 indicating pulmonary fibrosis while 147 (25.7%) of the high dose group verses 121 (20.7%) of the low dose group met the case definition of pulmonary fibrosis (restrictive or mixed spirometry and/or parenchymal disease) (p < 0.05). In a 2 × 4 table analysis (binary fibrosis x binary asbestos and radiation exposure) 90 (32.3%) in the high asbestos/ high radiation (> 20mSv deep dose) group met the cases definition for fibrosis vs. 81 (19.2%) in the low/low group (p =0.065). A dose response was seen for fibrosis risk with increasing radiation at exposure rates around the occupational standard.
Deep dose external radiation may add to the fibrotic effect of asbestos in workers exposed to both toxicants. The effect appears to be additive suggesting similar biological mechanisms for pulmonary fibrosis.
Worker protection standards are based upon single exposures not accounting for the constellation of exposures frequently encountered in the workplace.
T.K. Takaro, None.