Air Toxics Matter to More than Just Air

The U.S. EPA regulates hazardous air pollution under the Clean Air Act, designating 188 substances as ‘air toxics’. Despite this designation, air pollutants may partition to other environmental compartments and present risks through exposure routes other than inhalation. We use the USEtox multi-media fate model to determine which exposure routes contribute to overall intake fraction and disease risk for 60 air toxics that are present in the model. Inhalation was the dominant exposure route for intake fraction for the majority of air toxics considered, but for 13 cases (>20%), ingestion was dominant, particularly through consumption of above-ground produce. Disease risk showed similar patterns, with a contribution from inhalation of higher than 90% for approximately half of the air toxics considered and higher than 50% for another quarter, but with a dominant contribution from ingestion for the remaining quarter of substances. The results emphasize the continued need for careful communication of chemical risks that reflects complex partitioning and multiple potential exposure routes.