Groups of 50 male and 50 female B6C3F1 mice were exposed 6 hours per day, 5 days per week, for 60 to 61 weeks to air containing 0, 625, or 1250 parts per million 1,3-butadiene. These concentrations are somewhat below and slightly above the Occupational Safety and Health Administration standard of 1000 parts per million for butadiene. The study was designed for 104-week exposures but had to be ended early due to cancer-related mortality in both sexes at both exposure concentrations. There were early induction and significantly increased incidences of hemangiosarcomas of the heart, malignant lymphomas, alveolar-bronchiolar neoplasms, squamous cell neoplasms of the forestomach in males and females and acinar cell carcinomas of the mammary gland, granulosa cell neoplasms of the ovary, and hepatocellular neoplasms in females. Current workplace standards for exposure to butadiene should be reexamined in view of these findings.

This workshop provided a forum for discussion of methods and data needed to improve risk assessments of endocrine disruptors, with special emphasis on perturbations occurring during critical stages of development and on characterizing potential health effects at environmental exposure levels. Workshop participants were asked to suggest ways to make better use of our current knowledge on endocrine signaling pathways for quantitative evaluations of potential linkages between exposure to chemicals that perturb endocrine function and adverse health effects. Reports in the scientific literature and in the media have raised concerns that certain persistent environmental chemicals may be producing adverse effects in wildlife and in humans by interfering with the endocrine system. Some of the effects include reproductive and developmental abnormalities, increases in certain hormone-related cancers (breast, prostate, testis), and declines in wildlife populations. The term endocrine disruptors is used to describe exogenous agents that act by mimicking or antagonizing natural hormones in the body that are responsible for maintaining homeostasis and controlling normal development. Because hormone receptor systems are similar in humans and animals, effects observed in wildlife species raise concern of potential human health effects. Evaluating potential low-dose effects of environmental estrogens was identified as a major research priority at the 1997 NIEHS conference "Estrogens in the Environment." The format of the present workshop, as well as the specific issues that needed to be addressed, was conceived by an organizing committee composed of K.

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