A major ingredient used in manufacturing synthetic rubber and resin, 1,3-butadiene, has been found to cause cancer in laboratory rodents. About 70,000 workers in the chemical and rubber industries are potentially exposed to this compound.

The present OSHA standard for 1,3-butadiene, codified as 29 CFR 1910.1000, Table Z-1, was adopted in 1971 under the authority of Section 6(a) of the Occupational Safety and Health Act. This OSHA standard for 1,3-butadiene is an 8-hour time-weighted average exposure limit of 1,000 parts per million parts of air (1,000 ppm).

In 1976, the International Institute of Synthetic Rubber Producers, Inc. (IISRP) commissioned 90-day and 2 year inhalation toxicology studies on rats at Hazelton Laboratories, United Kingdom. In 1980, a teratology study on rats was initiated at Hazelton Laboratories, U.K. The carcinogenicity study was completed in November 1981. IISRP also commissioned an epidemiologic study of synthetic rubber workers. The study was performed by the School of Public Health, Johns Hopkins University, and the findings were reported in June 1982.

In 1981, the National Toxicology Program (NTP) initiated a laboratory animal (mice) inhalation study at Battelle Northwest. The final report is not yet available. Results of the studies commissioned by IISRP demonstrated the potential for 1,3-butadiene to cause cancer and reproductive effects in rats of exposure levels of 1,000 and 8,000 ppm. Preliminary findings from the NTP study confirm the carcinogenic potential at exposure levels of 625 and 1,250 ppm in mice.

The retrospective mortality study contracted at John Hopkins University assessed the mortality experience of workers in production plants in the United States and Canada during the period 1943-1979. The final study population was 13,920 workers. The study results showed all cancer mortality to be less than that for the general population. There was no statistically significant elevation in standardized mortality ratios for specific cancers. There were no statistically significant findings based on latency analysis. No attempt was made to include work environment exposure information in the analyses because information was not reliable or not available.

In addition to the above information, OSHA is aware that Meinhandt et. al. (Scand. J. Environ Health 8, 1982, 250-259) has published results of an environmental epidemiologic investigation of the styrene-butadiene rubber industry. No statistically significant excess in cause-specific mortality was reported in the study.

The results of the rodent toxicology studies triggered concern within OSHA regarding the adequacy of the existing OSHA exposure standard for 1,3-butadiene. On September 15, 1983, representatives from unions, industry, government and the university community concerned with the adequacy of the existing OSHA standard met at OSHA headquarters in Washington, D.C. The meeting was held in order to discuss the significance of available information as it is gathered. On January 5, OSHA published an announcement in the Federal Register stating that OSHA is joining with the Environmental Protection Agency (EPA) in requesting that interested parties submit to the public docket data and comments relevant to the determination of risks associated with potential adverse health effects resulting from 1,3-butadiene exposure. The comment period ended on March 5, 1984. A Federal Register notice announcing the extension of the comment period is being prepared.

IISRP has submitted worker exposure data for 1,3-butadiene which were collected in eight North American polymer plants between 1978 and 1984. The total number of measurements determined was 1,672 for a variety of 1,3-butadiene occupational exposures. Worker exposures were 25 ppm or less in 97.5 percent of the 8-hour time-weighted average exposures evaluated. Levels for 94.7 percent of the exposures measured were 10 ppm or less. It is our understanding that additional exposure information will be provided in the near future as a result of EPA contractor and National Institute for Occupational Safety and Health (NIOSH) workplaces studies.