The research by the University of Edinburgh measured the impact of diesel exhaust fumes on healthy volunteers at levels that would be found in heavily polluted cities. The team compared how people reacted to the gases found in diesel fumes—such as carbon monoxide and nitrogen dioxide—with the ultrafine chemical particles from exhausts.

The research, funded by the British Heart Foundation, shows that the particles, and not the gases, impaired the function of blood vessels that control how blood is channelled to the body’s organs.

A number of pollutants in diesel exhaust emissions are considered harmful to human health including fine particles, nitrogen dioxide, sulfur dioxide, and volatile organic compounds. The scientists had earlier shown that exposure to nitrogen dioxide, at levels in excess of those found in the present study, does not alter vascular function. However, they noted, it would not be possible to assess the importance of all the components of diesel exhaust individually “and such a strategy would not account for potentially important synergistic interactions between pollutants.”

The present study was thus designed specifically to determine the role of nanoparticulate emissions, and whether the organic and inorganic surface compounds, or the carbonaceous particles themselves, are the main arbiter of the adverse cardiovascular effects.

When assessed in the clinic, we showed that the vascular dysfunction associated with diesel exhaust inhalation is prevented by particle filtration. However, the nature of the particles appears to be critical since a pure carbon nanoparticulate exposure alone had no discernible effect on vascular function. Investigating this further, we were able to demonstrate that combustion-derived diesel exhaust nanoparticulate causes direct vascular dysfunction in vitro and this appears to be attributable to both soluble and insoluble fractions present on the surface of the particulate. Taken together, our findings suggest that the adverse vascular effects of diesel exhaust inhalation are predominantly mediated by combustion-derived nanoparticulate.

...The particles in diesel exhaust are laden with surface organic compounds from unburned hydrocarbon fuels, and coated with oxidized transition metals added to the fuels to improve efficiency. Experimental studies have established that diesel exhaust particles induce cellular oxidative stress and up-regulate pro-inflammatory pathways.

Particle size, surface area, and surface chemistry are thought to be important determinants of these cellular effects. Whether inhaled nanoparticulate is capable of translocation into the circulation in humans remains uncertain, but many of the chemical species on the surface of these particles are hydrophilic, could diffuse across tight junctions into the pulmonary interstitium, and be released into the circulation to affect vascular function directly. In particular, the organic species absorbed on the surface of combustion-derived particles are chemically active and potentially harmful to human health.

—Mills et al.

The researchers noted that it is not possible to speculate further on the identity of the harmful surface constituents, but suggest that a better understanding of the detrimental components of diesel exhaust particulate will be necessary for the future evaluation of technologies designed to modify vehicle exhaust emissions.

Our research shows that while both gases and particles can affect our blood pressure, it is actually the miniscule chemical particles that are emitted by car exhausts that are really harmful. These particles produce highly reactive molecules called free radicals that can injure our blood vessels and lead to vascular disease. We are now investigating which of the chemicals carried by these particles cause these harmful actions, so that in the future we can try and remove these chemicals, and prevent the health effects of vehicle emissions.

—Dr. Mark Miller, of the University of Edinburgh’s Centre for Cardiovascular Science

The researchers suggest that their findings provide a rationale for testing environmental health interventions to reduce particulate emissions to establish whether they can reduce the incidence of cardiovascular events.

Resources

• Nicholas L. Mills, Mark R. Miller, Andrew J. Lucking, Jon Beveridge, Laura Flint, A. John F. Boere, Paul H. Fokkens, Nicholas A. Boon, Thomas Sandstrom, Anders Blomberg, Rodger Duffin, Ken Donaldson, Patrick W.F. Hadoke, Flemming R. Cassee, and David E. Newby (2011) Combustion-derived nanoparticulate induces the adverse vascular effects of diesel exhaust inhalation. Eur Heart J doi: 10.1093/eurheartj/ehr195