Synergistic Effects on Rat Lungs of Mixtures of Oxidant Air Pollutants (Ozone or Nitrogen Dioxide) and Respirable Aerosols

Abstract

A hitherto unexpected synergism between the oxidant air pollutants ozone or nitrogen dioxide and a respirable-sized aerosol of ammonium sulfate was observed during controlled exposures of rats to these substances. Response of rat lungs to these pollutants was quantitated by measurement of apparent collagen synthesis rates in vitro by lung minces from exposed animals. Dose-response curves to either O₃ or NO₂ were altered in the presence of 5 mg/m₃ of (NH₄)₂SO₄ aerosol. Morphometric and histologic observations of lungs from rats exposed to high levels of ozone, with and without concurrent exposure to the (NH₄)₂SO₄ particles, confirmed such synergistic effects. In a separate set of experiments, rats were exposed at near ambient levels to mixtures of ozone and sulfuric acid aerosol (submicron-sized aerosol). Potentiation of ozone effects on lung collagen synthesis rates was also observed in these experiments. These observations may have broad implications for the appropriate evaluation of laboratory data in the setting of ambient air quality standards and/or threshold limit values for occupational safety.