Environmentally Persistent Free Radicals: Linking Air Pollution and Poor Respiratory Health?

Epidemiological relations between exposure to air pollution (both indoor and outdoor) and adverse respiratory outcomes, are examined. Although oxidative stress (OS) is presumed to be involved, a direct culprit is lacking. A proposal of a recently recognized by-product of thermal and combustion process that is capable of inducing OS as the missing link between exposure and respiratory disease, is presented. These products are called environmentally persistent free radicals (EPFRs). However, EPFRs persist in both the environment and biological systems for prolonged periods of time. An increasing number of studies are demonstrating the presence of EPFRs in a variety of environmental settings which include traffic-related air pollution (TRAP), coal dust and other combustion residues.