An assessment of air toxics in Minnesota

We used monitoring and modeling to assess the concentrations of air toxics in the state of Minnesota. Model-predicted concentrations for 148 hazardous air pollutants were from the U.S. Environmental Protection Agency Cumulative Exposure Project (1990 data). Monitoring data consisted of samples of volatile organic compounds, carbonyls, and particulate matter less than or equal to 10 mu m in aerodynamic diameter collected at 25 sites throughout the state for varying periods of time (up to 8 years; 1991-1998). Ten pollutants exceeded health benchmark values at one or more sites by modeling, monitoring, or both (including acrolein, arsenic, benzene, 1,3-butadiene, carbon tetrachloride, chromium, chloroform, ethylene dibromide, formaldehyde, and nickel). Polycyclic organic matter also exceeded the benzo[a]pyrene health benchmark value assumed to represent this class of pollutants. The highest modeled and monitored concentrations of most pollutants were near the center of the Minneapolis-St. Paul metropolitan area; however, many smaller cities throughout the state also had elevated concentrations. Where direct comparisons were possible, monitored values often tended to exceed model estimates. Upper-bound excess lifetime inhalation cancer risks were estimated to range from 2.7 x 10(-5) to 140.9 x 10(-5) (modeling) and 4.7 x 10(-5) to 11.0 x 10(-5) (using a smaller set of monitored carcinogens). Screening noncancer hazard indices summed over all end points ranged from 0.2 to 58.1 (modeling) and 0.6 to 2.0 (with a smaller set of monitored pollutants). For common sets of pollutants, the concentrations, cancer risks, and noncancer hazard indices were comparable between model-based estimates and monitored values. The inhalation cancer risk was apportioned to mobile sources (54%), area sources (22%), point sources (12%), and background (12%). This study provides evidence that air toxics are a public health concern in Minnesota.