1,3-Butadiene, a high-production volume chemical used largely in the manufacture of
synthetic rubber, is a multiple organ
carcinogen in rats and mice. In inhalation studies conducted in mice by the National Toxicology Program, high rates of early lethal
lymphomas occurring at exposure levels of 625 ppm or higher reduced the development and expression of later developing
tumors at other sites. Use of survival-adjusted
tumor rates to account for competing risk factors provided a clearer indication of the dose responses for 1,3-butadiene-induced
neoplasms. An increase in lung
tumors in female mice was observed at exposure concentrations as low as 6.25 ppm, the lowest concentration ever used in a long-term carcinogenicity study of this gas. Human exposures to
1,3-butadiene by workers employed at facilities that produce this chemical and at facilities that produce
styrene-butadiene rubber have been measured at levels higher than those that cause
cancer in animals. Furthermore, epidemiology studies have consistently revealed associations between occupational exposure to
1,3-butadiene and excess mortality due to lymphatic and hematopoietic
cancers. In response to the carcinogenicity findings for
1,3-butadiene in animals and in humans, the Occupational Safety and Health Administration has proposed lowering the occupational exposure standard for this chemical from 1000 ppm to 2 ppm. Future work is needed to understand the mechanisms of
tumor induction by 1,3-
butadiene; however, the pursuit of this research should not delay the reduction of human exposure to this chemical.