Objectives To investigate possible associations between silica dust exposure and death from chronic obstructive pulmonary diseases (COPD) and silicosis in German uranium miners.
Methods The cohort consists of 58,672 miners comprising 2,167,600 person-years and 25,239 deaths in the follow-up period 1946–2008. A detailed job-exposure matrix was used to estimate the cumulative exposure to crystalline silica in mg/m3-years. The total numbers of underlying causes of death from COPD (ICD-10 code: J40-J44) or silicosis (J62-J65) was determined based on certificates of death and autopsy files. Internal Poisson regression with baseline-stratification by age, calendar year and duration of employment was used to estimate the relative risk (RR) and 95% confidence limits (CI) in different categories of cumulative exposure to silica dust for mortality from COPD and silicosis.
Results Nearly all cohort members were exposed to silica dust at some stage with a wide exposure range (mean = 5.9, max = 56 mg/m³-years). No increase in risk with increasing cumulative silica dust was found for COPD as underlying cause of death only (n = 719), whereas statistically significantly increased RR’s in exposure categories above 10 mg/m3-years were found when COPD was considered as underlying or contributing cause of death (n = 2,675). The corresponding RR in the highest exposure category of 30 or more compared to less than 0.5 mg/m3-years was 2.2 (95% CI: 1.6–2.8). The RR for silicosis as underlying cause of death (n = 976) compared to the reference category 0–2 mg/m3-years increased systematically with increasing exposure from RR = 2.8 (95% CI: 1.03–4.6) to 118.1 (95% CI: 50.3–188.0) in the exposure categories 2–5 and 30 or more mg/m3-years, respectively.
Conclusions Mortality of silicosis is confirmed to be associated with cumulative silica dust exposure even at low levels. Results indicate that death from COPD is related to silica dust, when considering underlying and contributing causes of death.
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