Wastewater exposure and health--a comparative study of two occupational groups.

AIMS To investigate whether wastewater workers are at increased risk of developing cancer. METHODS Two cohorts of workers employed by the City of Copenhagen, 591 wastewater workers and 1545 water supply workers (controls), were followed from 1965 until 1998. These two cohorts were compared in terms of cause specific mortality and cancer incidence. RESULTS The wastewater workers' mortality exceeded that of the controls (relative risk (RR) = 1.25, 95% CI: 1.03 to 1.51). A similar small excess was seen for cancer incidence (RR = 1.27, 95% CI: 0.97 to 1.67). Though rare, there was a strongly increased incidence of primary liver cancer among the wastewater workers (RR = 8.9, 95% CI: 1.5 to 51.5). CONCLUSION The excess mortality seen among the wastewater workers was smaller than originally feared. It may partly have been due to their occupational exposure, and for preventive purposes, exposure to wastewater and sludge should be minimised. The possibility that sewage exposure confers an increased risk of primary liver cancer deserves further investigation.