Abstract
Objectives:To assess whether cancer incidence, mainly from lymphohaematopoietic tumours and breast cancer, and mortality were increased in a cohort of Swedish sterilant workers exposed to low levels of ethylene oxide (EtO), updated with 16 more years of follow up.Methods:The mortality and cancer incidence 1972–2006 experienced by a cohort of 2,171 male and female workers employed for at least one year in two plants producing medical equipment sterilised with EtO were investigated. Individual cumulative exposure to EtO was assessed by occupational hygienists. Cause-specific standardized rate ratios were calculated using the regional general population as a comparison for mortality (SMR) and cancer incidence (SIR). Internal Poisson-regression analyses were performed for selected causes.Results:The median cumulative exposure to EtO was 0.13 ppm-years. The overall cancer incidence was close to unity (SIR 0.94, 95% CI 0.82–1.08). Eighteen cases of lymphohaematopoietic cancer were observed (SIR 1.25, 95% CI 0.74–1.98). A healthy worker effect was indicated from a significantly decreased overall mortality and mortality from cardiovascular diseases. Internal analyses found significantly increased rate ratios for breast cancer for the two upper quartiles of cumulative exposure as compared to the lowest 50% of the cohort (IRR 2.76, 95% CI 1.20–6.33 and IRR 3.55, 95% CI 1.58–7.93).Conclusions:The findings from this updated study indicate limited or low risks for human cancer due to occupational exposure from ethylene oxide at the low cumulative exposure levels in this cohort. However a positive exposure-response relation with breast cancer was observed though.
Highlights
Internal analysis of cancer incidence (Incidence rate ratio, Incidence Rate ratio (IRR)) between exposure categories within the cohort were performed by means of Poisson regression [19] using EGRET software (Statistics and Epidemiology Research Corporation, Seattle)
The Standardized Incidence Ratio (SIR) for overall cancer incidence in the external comparisons was close to unity, with 203 observed malignant tumours, compared with 216 expected (SIR 0.94, 95% confidence intervals (95% CIs) 0.82–1.08)
Eighteen cases of lymphohaematopoietic cancer were observed (SIR 1.25, 95% CI 0.74–1.98)
Summary
The cohort comprised 2,171 workers (1,309 females and 862 males), employed for at least one year prior to 1986, at two plants producing medical equipment sterilised with EtO. Vital status in the cohort was determined on 31 December 2006 (Table 1). In plant A the sterilisation operations started in 1970 and ceased in 1994. The initial exposures in 1970 could be as high as 40 ppm. Thereafter, the levels have continuously decreased, and since 1985 only sterilisers have had eight hour time-weighted exposures exceeding 0.2 ppm. Plant B started sterilising in 1964, and the process ceased in 2002. With initial peak exposure levels of 75 ppm in 1964 plant B has had a continuous decrease of exposure, and since 1985 only sterilisers and some store workers have had eight hour time-weighted exposures >0.2 ppm
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