Cancer mortality in 40,761 employees of three UK nuclear industry facilities who had been monitored for external radiation exposure was examined according to whether they had also been monitored for possible internal exposure to
tritium,
plutonium or other
radionuclides (
uranium,
polonium,
actinium or other unspecified). Death rates from
cancer were compared both with national rates and with rates in radiation workers not monitored for exposure to any
radionuclides. Among workers monitored for
tritium exposure, overall
cancer mortality was significantly below national rates [standardized mortality ratio (SMR) = 83, 165 deaths; 2P = 0.02] and none of the
cancer-specific death rates was significantly above either the national average or rates in non-monitored workers. Although the overall death rate from
cancer in workers monitored for
plutonium exposure was also significantly low relative to national rates (SMR = 89, 581 deaths; 2P = 0.005), mortality from pleural
cancer was significantly raised (SMR = 357, nine deaths; 2P = 0.002); none of the rates differed significantly from those of non-monitored workers. Workers monitored for
radionuclides other than
tritium or
plutonium also had a death rate from all
cancers combined that was below the national average (SMR = 86, 418 deaths; 2P = 0.002) but
prostatic cancer mortality was raised both in relation to death rates in the general population (SMR = 153, 37 deaths; 2P = 0.02) and to death rates in radiation workers who had not been monitored for exposure to any
radionuclide [rate ratio (RR) = 1.65; 2P = 0.03]. Mortality from
cancer of the lung was also significantly increased in workers monitored for other
radionuclides compared with those of radiation workers not monitored for exposure to
radionuclides (RR = 1.31, 164 deaths; 2P = 0.01). For
cancers of the lung, prostate and all
cancers combined, death rates in monitored workers were examined according to the timing and duration of monitoring for
radionuclide exposure, with rates of radiation workers not monitored for any
radionuclide forming the comparison group. In
tritium-monitored workers, RRs for
prostatic cancer varied significantly according to the number of years in which they were monitored (2P = 0.03). In workers monitored for
plutonium exposure, RRs for all
cancers combined increased with the number of years in which they were monitored (2P = 0.04) and with the number of years since first monitoring (2P = 0.0003). There was little suggestion of systematic variation in RRs for workers monitored for other
radionuclides in relation to the timing or duration of monitoring, nor did it appear that their raised rates of
cancer of the lung and prostate were explained by external radiation dose. These analyses of
cancer mortality in relation to monitoring for
radionuclide exposure reported in a large cohort of nuclear industry workers suggest that certain patterns of monitoring for some
radionuclides may be associated with higher death rates from
cancers of the lung, pleura, prostate and all
cancers combined. Some of these findings may be due to chance. Moreover, because of the paucity of related data and lack of information about other possible exposures, such as whether
plutonium workers are more likely to be exposed to
asbestos, firm conclusions cannot be drawn at this stage. Further investigations of the relationship between
radionuclide exposure and
cancer in nuclear industry workers are needed.