The mixture of particulates and chemicals found in urban air is more toxic to lung cells than a common test suggests, report researchers at the University of North Carolina, Chapel Hill (Environ. Sci. Technol., DOI: 10.1021/es301431s). The finding sheds light on how the complex blend of particulates, gases, and semivolatile species in urban air may affect health.
Atmospheric chemist Harvey E. Jeffries and collaborators used a sunlit rooftop chamber to combine freshly generated car diesel exhaust with a mix of volatile organic chemicals simulating urban air. They compared two methods for measuring the concoction’s toxicity: directly exposing human lung cells to particulates in chamber air with an electrostatic system and a widely used method—filtering the air, resuspending filtered particulates in a solution, and applying this mixture to lung cells.
Cells directly exposed to the particulates in the chamber react with inflammation; those treated with resuspended particulates have no such response, the researchers found. On the basis of liquid chromatography/mass spectrometry analyses, the team attributes the difference to semivolatile carbonyl compounds, which coat particles in air but are lost during filtration.
Secondary organic compounds such as the semivolatile carbonyls form when sunlight reacts with volatile organic chemicals in air. Previous studies show that a coating of such compounds makes particulates more toxic. Exhaust particles coated with the compounds can potently deliver them to the lungs, Jeffries says.
Developing an exposure system that “represents the real world but can be replicated for experimental purposes is a tough challenge,” says Joel D. Kaufman, an epidemiologist at the University of Washington, Seattle. The researchers have demonstrated one of many particle properties that might have toxic importance that the filtration method misses, he says.
Many toxicologists are shifting to similar exposure systems or to in vivo studies using direct inhalation of pollutant mixtures, Kaufman says.
The North Carolina group has patented a breadbox-sized version of their system, which is designed for field-based studies. They plan to market it through a new company called BioDeptronix, says founder and study coauthor William Vizuete.