Estimating cancer risk from outdoor concentrations of hazardous air pollutants in 1990

A public health concern regarding hazardous air pollutants (HAPs) is their potential to cause cancer. It has been difficult to assess potential cancer risks from HAPs, due primarily to lack of ambient concentration data for t he general population. The Environmental Protection Agency's Cumulative Exp osure Project modeled 1990 outdoor concentrations of HAPs across the United States, which were combined with inhalation unit risk estimates to estimat e the potential increase in excess cancer risk for individual carcinogenic HAPs, These mere summed to provide an estimate of cancer risk from multiple HAPs. The analysis estimates a median excess cancer risk of 18 lifetime ca ncer cases per 100,000 people for all HAP concentrations. About 75% of esti mated cancer risk was attributable to exposure to polycyclic organic matter , 1,3-butadiene, formaldehyde, benzene, and chromium. Consideration of some specific uncertainties, including underestimation of ambient concentration s, combining upper 95% confidence bound potency estimates, and changes to p otency estimates, found that cancer risk may be underestimated by 15% or ov erestimated by 40-50%. Other unanalyzed uncertainties could make these unde r- or overestimates larger. This analysis used 1990 estimates of concentrat ions and can be used to track progress toward reducing cancer risk to the g eneral population.