An updated study of mortality among workers at a petroleum manufacturing plant

Our plain-English summary of An updated study of mortality among workers at a petroleum manufacturing plant, by Y. Honda, E. Delzell, P. Cole (Journal of Occupational and Environmental Medicine, 1995).

The study

• Authors: Y. Honda, E. Delzell, P. Cole
• Journal: Journal of Occupational and Environmental Medicine
• Published: 1995;37(2):194-200
• Cited by: 56 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

This study evaluated mortality among 9796 white male workers at a petroleum-manufacturing plant. The main purpose was to examine recent patterns in leukemia mortality, for which an increase had been reported in an earlier investigation. Compared to U.S. white men, the cohort had an excess of leukemia in 1940-1979 (38 observed/23 expected; standardized mortality ratio = 168; 95% confidence interval = 119-230). In the 1980s, there was a deficit of leukemia (8 observed/14 expected; standardized mortality ratio = 55; 95% confidence interval = 24-108). However, this was balanced by an excess of myelofibrosis and myelodysplasia (4 observed, < 1 expected). These results indicate that any occupational leukemogenic exposures at the plant have been reduced to a point at which they are insufficient to cause leukemia. Hourly workers also had an excess of deaths from mesothelioma in the 1980s (8 observed, about 2.5 expected), possibly because of exposure to asbestos in the past.

In plain English

This study updated the mortality follow-up of 9796 white male workers at a petroleum-manufacturing plant in southern Illinois. It compared their deaths through 1989 with rates for U.S. white men, and its main focus was leukemia. Overall, the workers had fewer deaths than expected from all causes and from all cancers. Leukemia deaths were above expectation in 1940–1979 (38 observed, 23 expected; SMR 168, 95% CI 119–230) but below it in 1980–1989 (SMR 55, 95% CI 24–108). Hourly workers had more deaths than expected from myelofibrosis or myelodysplastic syndrome. Reviewing death certificates, the authors found nine mesothelioma deaths, all in hourly workers and eight in or after 1980. Several of these men had jobs such as pipefitter, insulator or carpenter that may have involved asbestos exposure. With expected numbers estimated from cancer-incidence rates, the mesothelioma SMR was 200 (CI 92–380) overall and 320 (CI 138–630) for the 1980s. The authors said these figures may be underestimates. They suggested the excess may be due to asbestos, and concluded that any leukemia-causing exposures at the plant had been reduced below the level needed to cause leukemia.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Updated retrospective mortality follow-up (cohort) study comparing the workers' death rates with those of the U.S. white male population, using standardized mortality ratios (SMRs)
• Who was studied: 9796 white male workers at a petroleum-manufacturing plant in southern Illinois. They had worked at least 6 months before 1990, and were either hourly workers employed at any time from 1942 through 1989 or salaried workers employed at any time through 1989. Follow-up ran to January 1, 1990.
• Exposure: Employment at a plant doing crude oil refining and making fuels, lubricating oils, asphalt and petrochemicals including benzene. No exposure measurements were reported. Asbestos was considered only through the job titles of the men who died of mesothelioma, several of whose jobs may have entailed asbestos exposure.
• Main results:
  • Overall cohort, 1940–1989: all-causes SMR 79 (3627 deaths) and all-cancers SMR 88 (868 deaths), both statistically significant deficits
  • Overall cohort: leukemia excess in 1940–1979, 38 observed versus 23 expected (SMR 168, 95% CI 119–230)
  • Overall cohort: fewer leukemia deaths than expected in 1980–1989 (SMR 55, 95% CI 24–108)
  • The 1980–1989 leukemia deficit came from hourly workers: 4 leukemia deaths compared with 12 expected
  • Salaried workers had a statistically significant leukemia excess, restricted to 1940–1984: 11 observed versus 5.1 expected (SMR 216, 95% CI 108–386)
  • Hourly workers: six deaths from myelofibrosis or myelodysplastic syndrome (MF/MDS) in 1940–1989, four of them in 1985–1989. The approximate expected number was less than 0.50 for each period and less than 1.0 overall; the increases were statistically significant for 1985–1989 and 1940–1989.
  • Death-certificate review found nine mesothelioma deaths in the cohort, eight of them in or after 1980
  • All the men with mesothelioma were hourly workers, and all but two started work at the plant before 1950
  • Mesothelioma, using SEER incidence rates to estimate expected numbers (about 0.5 for 1942–1969, 1.5 for 1970–1979 and 2.5 for 1980–1989): SMR 200 (CI 92–380) overall
  • Mesothelioma SMR for the 1980s: 320 (CI 138–630)
  • The authors suggested the mesothelioma excess may be due to asbestos, an established cause of mesothelioma, because several of the men had potential for asbestos exposure in their jobs
• The authors' conclusion: The authors concluded that any occupational leukemia-causing exposures at the plant had been reduced to a point at which they are insufficient to cause leukemia
• Limitations the authors state:
  • Expected mesothelioma deaths could not be calculated from national mortality rates because these are not available for this cancer. Expected numbers were instead estimated from SEER incidence rates, assuming that rates before 1970 were one-half the 1973–1980 rates or lower.
  • The mesothelioma SMRs may be underestimates, because incidence rates in the general population are higher than mortality rates
  • The leukemia deficit in the 1980s may be due to chance, or to problems with certifying leukemia as the underlying cause of death
  • The slight leukemia excess among salaried workers in 1980–1989 (4 observed versus 2.4 expected) was based on small numbers

Topics

Medical terms in this study, explained in our Lexicon: standardized mortality ratio (SMR), confidence interval, Mesothelioma.

Related studies

• An updated mortality study of workers at a petroleum refinery in Beaumont, Texas — G.K. Raabe, K.W. Collingwood, et al. (1998)
• Updated mortality among diverse operating segments of a petroleum company — R.J. Lewis, A.R. Schnatter, et al. (2000)
• Asbestos exposure and cancer mortality among petroleum refinery workers: a Poisson regression analysis of updated data — F. Montanaro, M. Ceppi, et al. (2004)
• Long-term follow-up mortality study of petroleum refinery and chemical plant employees — S.P. Tsai, E.L. Gilstrap, et al. (1996)
• Updated epidemiological study of workers at two California petroleum refineries, 1950-95 — K.P. Satin, W.J. Bailey, et al. (2002)
• Update of a prospective study of mortality and cancer incidence in the Australian petroleum industry — R.T. Gun, N.L. Pratt, et al. (2004)

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