Retrospective cohort mortality study and nested case-control study of workers exposed to creosote at 11 wood-treating plants in the United States.

OBJECTIVE

The objective of this study was to assess both malignant and nonmalignant mortality risks of workers exposed to creosote. For background, a literature review is also presented.

METHODS

The retrospective cohort study consisted of 2179 employees at 11 plants in the United States where wood (primarily railroad ties and utility poles) is treated with creosote-based preservatives. The observation period covered 1979-2001. Mortality data in the cohort study were analyzed in terms of cause-specific standardized mortality ratios (SMRs) and 95% confidence intervals (95% CIs), with expected deaths based on U.S. national cause-, gender-, race-, year-, age-specific mortality rates. In addition to the cohort investigation, a nested case-control study of lung cancer and multiple myeloma was conducted. Information on tobacco consumption and detailed employment (job titles) was obtained for cases and matched controls. Jobs were classified into 5 categories according to potential for exposure to creosote. Odds ratios (ORs) and 95% CIs were calculated for job categories and length of exposure.

RESULTS

Overall mortality for the entire cohort was lower than expected (293 observed deaths vs. 325.37 expected, SMR = 90.1, 95% CI = 80.0-101.0). Close to 90% employees were hourly, whose potential for exposure was generally much higher than that of salaried employees. Among hourly employees, except for multiple myeloma, none of the specific cancer sites showed any significant increase. Furthermore, detailed analysis by length of employment did not reveal any significant mortality excess or upward trend. Six deaths were from multiple myeloma, whereas 1.50 deaths were expected (SMR = 401.1, 95% CI = 147.2-873.1). However, analysis by length of employment did not show any upward trend for multiple myeloma. No significant mortality increase was reported for any nonmalignant disease, and analysis by length of employment did not reveal any upward trend. In the case-control study, an increased risk of lung cancer was associated with tobacco consumption (OR = 4.92) but not with any job/exposure category. For example, the lung cancer odds ratio for routine exposure to creosote-based wood preservatives was 0.58 (95% CI = 0.11-3.03). Similarly, case-control analyses of multiple myeloma did not reveal any association with employment at the plants or with exposure to creosote-based wood preservatives or to creosote-treated products.

CONCLUSIONS

Based on the present investigation and other studies, there was no evidence that employment at the 11 wood-treating plants or exposure to creosote-based wood preservatives was associated with any significant mortality increase from site-specific cancers or nonmalignant diseases. Some results should be interpreted with caution because they were based on small numbers.