Mortality patterns among industrial workers exposed to chloroprene and other substances: II. Mortality in relation to exposure
Introduction
Chloroprene (2-chloro-1,3 butadiene) (CD) is a monomer used almost exclusively for the production of synthetic rubber and latexes [1]. The chemical structure of CD is similar to that of vinyl chloride, a known human carcinogen [2]. CD is classified by the International Agency for Research on Cancer as a possible human carcinogen (group 2B) based on sufficient evidence of carcinogenicity in experimental animals [3]. Epidemiological data on the carcinogenicity of CD are available from five cohort studies of chloroprene production workers in the U.S. [4], China [5], Armenia [6] and France [7], and the study of shoe manufacturing workers in Russia [8]. An increased risk of liver [5], [6], [8], [9] and lung cancer [7] has been suggested by some of these studies. The inherent methodological limitations in the previous epidemiology studies raise questions; however, about their significance regarding human cancer risks [10], [11].
To provide more definitive and comprehensive epidemiological evidence regarding the long-term health effects of exposure to CD, a four-plant, multi-national epidemiologic study of workers with potential exposure to CD was commissioned in 1999 by the International Institute of Synthetic Rubber Producers (IISRP). The exposure assessment component of the study was conducted at the University of Oklahoma (UOk) and the University of Illinois at Chicago (UIC); the epidemiology and biostatistics component was conducted at the University of Pittsburgh (UPitt). Our analysis of general mortality patterns among the CD cohort, reported in a companion paper [12], found no evidence of elevated mortality risks from any of the causes of death examined, including all cancers combined and lung and liver cancer, the sites of a priori interest. We report here the results of our detailed analysis of mortality from all cancers combined, lung and liver cancer in relation to quantitative measures of CD and VC exposure.
Section snippets
Study sites and subjects
The chloroprene (CD) cohort included all workers (n = 12,430) with potential CD exposure at one of four CD production sites from plant start-up date through the end of 2000 (1999 for one site). The sites include two DuPont/Dow Elastomers LLC (DDE) plants in the U.S. (Louisville, KY and Pontchartrain, LA), one DDE plant in Maydown, Northern Ireland (NI) and one Enichem Elastomers France plant in Grenoble, France (FR) (called here plants L, P, M and G). CD production dates for each plant were: L
Results
Table 4, Table 5, Table 6, Table 7, Table 8 show for plants L, M, P and G, respectively, the results of our exposure-response analyses based on internal and external comparisons. Results for the internal comparisons include for each category of the exposure measures considered, the number of observed deaths (cases) and associated non-cases summed across individual risk sets. The external comparisons include the number of person-years accumulated in each exposure category. For plant L (Table 4),
Discussion and conclusions
As described in detail in our analysis of general mortality patterns [12], our historical cohort study of workers from four CD production sites in the U.S. and Europe represents the largest and the most comprehensive and rigorous investigation of the long-term health effects of exposure to CD conducted to date. It overcomes most of the shortcomings and uncertainties noted by Rice and Bofetta [10] and Acquavella and Leonard [11] that have limited the interpretation of findings from the five
Acknowledgements
The International Institute of Synthetic Rubber Producers (IISRP) sponsored this research, but the design, conduct, analysis and conclusions are those of the authors. Sponsoring companies were DuPont Dow Elastomers LLC and Enichem Elastomers France. We would like to acknowledge the cooperation and support of the representatives and consultants of IISRP and its member companies, in particular, Sheila Jones, Robin Leonard, Mike Lynch, Stuart Pollard and Paul Poullet. Our special thanks to Dr.
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