Chronic Bronchitis in the Cohort of Mayak Workers First Employed 1948–1958

Abstract

Incidence of chronic bronchitis has been studied in a cohort of 12,210 workers first employed at one of the main plants of the Mayak nuclear facility during 1948-1958 and followed up to 31 December 2005. Information on external gamma doses is available for virtually all of these workers; in contrast, plutonium body burden was measured only for 30% of workers. During the follow-up period in the study cohort 1,175 incident cases of chronic bronchitis were verified. The analyses of nonradiation factors revealed that the underlying risk of chronic bronchitis incidence increased with increasing attained age and was higher among smokers compared with never-smokers as would be expected. The most interesting finding in relationship to nonradiation factors was a sharp increase in the baseline chronic bronchitis risk before 1960. The cause of this is not clear but a number of factors may play a role. Based on the follow-up data after 1960, the analysis showed a statistically significant linear dose response relationship with cumulative external gamma-ray dose (ERR/Gy = 0.14, 95% CI 0.01, 0.32). Based on the same subset but with an additional restriction to members with cumulative internal lung dose below 1 Gy, a statistically significant linear dose response relationship with internal alpha-radiation lung dose from incorporated plutonium was found (ERR/Gy = 2.70, 95% CI 1.20, 4.87). In both cases, adjustment was made for nonradiation factors, including smoking and either internal or external dose as appropriate. At present there are no similar incidence studies with which to compare results. However, the most recent data from the atomic bomb survivor cohort (the Life Span Study) showed statistically significant excess mortality risk for respiratory diseases of 22% per Gy and this value is within the confidence bounds of the point estimate of the risk from this study in relation to external dose.

Chronic bronchitis incidence in the extended cohort of Mayak workers first employed during 1948–1982

“…When compared with the previous study of MWC:1948–1958, 8 the size of MWC:1948–1982 has increased by 45% with follow-up period extended by 3 years. Table 1 shows summary characteristics of both cohorts.…”

“…As medical criteria to diagnose CB as well as ICD, in particular, the rules to code respiratory diseases, were changed over the studied follow-up period, CB diagnosis originally registered in medical records might not be sufficiently reliable for an epidemiological analysis 8. Thus, all cases in MWC:1948–1982 were retrospectively reviewed by experts similarly to the previous study.…”

“…Findings from the first analysis8 of CB incidence (491 code of the 9th revision of International Classification of Diseases)9 in the cohort of workers first employed at one of the Mayak PA main plants, that is, reactors, plutonium or radiochemical, in 1948–1958 and followed up through the end of 2005 based on occupational radiation dose estimates from Doses-2005 dosimetry system were published elsewhere. Hereinafter, this cohort is referred to as MWC:1948–1958 .…”

Biological Effectiveness of Ionizing Radiation: Acute vs. Protracted Exposures

“…and digestive systems, was reported in [22], which can be seen as circumstantial evidence in favor of dose-related differences in medical surveillance and self-reporting, a phenomenon noticed also by other researchers in populations exposed to radiation [28], discussed in [29]. In the author's opinion, the dose-effect relationships with non-neoplastic diseases [30][31][32][33][34] call in question such relationships with cancer, reported e.g. in the studies [23,24,[35][36][37][38][39][40][41][42][43] including those cited in [2,25] in support of the DDREF lowering.…”

“…Although there may be some risk of cardiovascular disease at high dose and dose-rate exposures [16], existing data are insufficient to confirm a cause-effect relationship between radiation and cardiovascular diseases at doses below 1-2 Gy, while plausible biological mechanisms are unknown [44]. Average doses in the epidemiological studies [30][31][32][33][34] were lower. As mentioned above, people knowing their relatively high dose estimates would probably be on average more motivated to visit medical institutions (self-selection bias), being at the same time given more attention.…”