Significance of 1,3-butadiene to the US air toxics regulatory effort.

Because of its prevalence, particularly as a combustion by-product, 1,3-butadiene is a particularly important air toxic. It plays a significant role in all air toxics regulatory efforts in the US. The various requirements of the Federal Clean Air Act (CAA) dealing with air toxics are reviewed and the significance of 1,3-butadiene in each area is discussed in light of what is known about its emissions and health effects. The impacts of the changes in the understanding of 1,3-butadiene cancer potency over the past 15 years demonstrates the possible impact of such benchmarks and the importance of using the best science in understanding public health risks.