Mortality of power workers exposed to phenoxy herbicides and polychlorinated biphenyls in waste transformer oil

Herbicide spray crews employed by a Canadian power company between 1950 and 1967 had a higher than expected death rate, with a standardized mortality ratio of 157% (CI 130%-194%). In 1991, the cohort consisted of 225 former sprayers of whom 127 were still alive and 98 had died. Eligibility for inclusion in the cohort was based on employer records; and a history of spraying for 30 days or more in at least one spray season. Deaths expected were based on age-specific population mortality rates for New Brunswick. The all-age SMR for the total cohort was 159%. After 1958, however, waste transformer oil was added to the phenoxy-herbicide spray mixture, the oil representing 10% of the final mixture. Spray crews wore no protective clothing. Subdividing the cohort into spray years 1950-1958 and 1959-1967 yielded SMRs of 146% (CI 115%-184%); and 215% (CI 139%-318%), respectively. The transformer oil was used during the period 1959-1967. Most excess deaths were due to cardiovascular disease.