Human health risk assessment for exposures to 1,3-butadiene in the United States with input from an independent science advisory panel.

A human health risk assessment was conducted for potential cancer and noncancer effects of 1,3-butadiene (BD) using best available science, data, and methodologies. An independent panel of experts was engaged to provide input and guidance on key decisions made in the quantitative assessment. BD biomarker data played an important role in quantifying species differences, human variation, and quantifying smoking exposures. The assessment included consideration of nineteen scenarios for potential worker exposures, each of which include characterization of the impact of respirator use, and seven scenarios for aggregate exposures to BD across pathways. Monte Carlo methods were used to characterize uncertainty and variation risks and hazards from exposures to BD. The results of this assessment support three general conclusions: (1) ambient air is generally not an important source of BD exposure to the U.S. population when compared to other sources; (2) exposures to BD in the US are not expected to pose an unreasonable risk of cancer or noncancer effects; and (3) the existing OSHA PEL of 1 ppm is considered to be protective of the potential cancer risks and noncancer hazards from BD exposures.