Cancer incidence in the wastewater treatment plant of a large chemical company

Objectives To evaluate cancer incidence among employees assigned to BASF’s wastewater treatment plant. Methods We conducted a retrospective cohort study including 477 male employees who had ever worked in the facility for at least 1 year since the start of operations in 1974. Cancers were identified by review of occupational medical records and a standardized questionnaire completed by the participants or their next of kin. Confirmation through hospital records was sought for all reported cases after obtaining informed consent. Standardized incidence ratios (SIR) and 95% confidence intervals (CI) were computed using comparison data provided by the Saarland Cancer Registry. Further comparisons were made between three different subgroups of employees, working in maintenance, wastewater processing, and sewage sludge treatment. Results A total of 50 cancers were observed (SIR 1.14, CI 0.85–1.51). Colorectal (1.14, 0.42–2.48), bronchial (1.40, 0.67–2.57) and prostate (1.15, 0.42–2.50) were the most frequently observed cancers. Five cases of bladder cancer were found in the total cohort (1.75, 0.57–4.09), with four of them occurring in the sewage sludge treatment area (6.82, 1.86–17.46). Allowing for a 10-year lag did not significantly change the results. Conclusions The overall cancer experience among employees of the wastewater treatment plant was similar to that of the corresponding general population. The finding of an excess risk for bladder cancer in one subgroup of workers was unexpected with regard to the available literature. There is no straightforward explanation for this finding, and it may be due to chance. An extended follow-up of this cohort will take place after 5 years. Annual bladder cancer screening is offered to active and retired employees from this plant for the time being. The current working conditions and work practices have been re-assessed by occupational hygienists and deemed to be safe.