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 Cumulati ve Exposure Project (1990 data). Monitoring data consisted of samples of vo latile organic compounds, carbonyls, and particulate matter less than or eq ual 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 pollutan ts exceeded health benchmark values at one or more sites by modeling, monit oring, 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 cent er of the Minneapolis-St. Paul metropolitan area; however, many smaller cit ies throughout the state also had elevated concentrations. Where direct com parisons were possible, monitored values often tended to exceed model estim ates. 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 1 1.0 x 10(-5) (using a smaller set of monitored carcinogens). Screening nonc ancer hazard indices summed over all end points ranged from 0.2 to 58.1 (mo deling) and 0.6 to 2.0 (with a smaller set of monitored pollutants). For co mmon sets of pollutants, the concentrations, cancer risks, and noncancer ha zard indices were comparable between model-based estimates and monitored va lues. The inhalation cancer risk was apportioned to mobile sources (54%), a rea sources (22%), point sources (12%), and background (12%). This study pr ovides evidence that air toxics are a public health concern in Minnesota.