Mortality Studies "B"

NIOSH Cohort vs. Dow Cohort Comparison

The NIOSH study,  MA Fingerhut, et al, 1991¹, is an excellent study that compares the mortality experience of 5172 chemical workers at 12 plants in the US that produced chemicals contaminated with TCDD.

The NIOSH study found elevated cancer rates in twenty five (25) categories of cancers, including the extremely important “All Malignant Neoplasms”. The NIOSH report made this comment, “Moreover, a significantly increased SMR for all cancers combined is unusual in occupational studies of chemical workers. Results similar to ours were observed in a study of German workers workers exposed to TCDD after a 2,4,5-trichloropehnol reactor accident in 1953. A subgroup of the workers with chloracne (used as a surrogate for exposure) and at least 20 years of latency had an SMR of 201 … for all cancers combined, based on 14 deaths [7 expected]. This is the only other industrial cohort with both substantial exposure to TCDD and a long period of latency during which mortality was examined.”

Dow Chemical responded to the NIOSH study in GG Bond, Dioxin: A Case Study². 

“The results showed total mortality and cancer mortality among the 2,092 Dow employees in the study group to be comparable to expected levels; however, cancer mortality among the remaining 3,080 members of the cohort was elevated, particularly among men who worked for 1 year or longer in areas of potential exposure.”

It should be noted that the Dow article does not dispute that higher rates of cancer for the other 3,080 workers have been linked to TCDD exposure.

A side by side comparison of the mortality of the Dow employees and the employees of the other eleven companies has been summarized in an Excel spreadsheet.  Link to Dow-NIOSH Comparison

The comparison shows that Dow's cohort of chemical workers exposed to TCDD also has an elevated mortality (SMR 102) for All Malignant Neoplasms.  The comparison further shows that the Dow employees had the higher mortality for eight (8) cancer categories while the employees in the other eleven companies had the higher mortality in only five (5) cancer categories.

Comparison of Dow Mortality Studies

Dow has posted seven epidemiology studies that pertain to the health of its workers. Although, two of the studies are not dioxin-exposure specific, these two studies do provide valuable insight into the mortality of more than 35,000 Dow employees that worked in Dow's Midland and Bay City, MI sites.  The two non-dioxin studies show an elevated mortality from several cancers that are also elevated in the dioxin-related studies.  More information on these two studies can be found in "Mortality Studies - C"

A side-by-side comparison of all seven studies is extremely interesting in that the comparison clearly shows that mortality from several cancers is elevated across several studies. 

Although Dow might argue that some of the elevations are not "statistically significant", I believe that the clustering of elevated mortalities is a clear indication that the health of Dow employees has been adversely impacted by exposure to dioxins and even by chemical exposure in general.

The comparison only shows cancer categories that have a standardized mortality ratio equal to or greater than 110 (10% increase over expected).  Cancer categories that have a SMR = 110 in three studies have been shaded. 

           Link to Comparison of Dow Employee Mortalities

References

1. MA Fingerhut, et al, Cancer Mortality In Workers Exposed to 2,3,7,8-Tetrachlorodibenzo-p-dioxin, New England Journal of Medicine, Jan. 24, 1991, 212-218

2. GG Bond, Dioxin: A Case Study, Am Jour Indust Med, 23: 177-182 (1993)