A review of the toxicology of air pollutants: toxicology of chemical mixtures.

On a temporal basis, air has immense capacity for moving a large mass of pollutants. Mammals and birds are exposed to pollutants in air by the inhalation (nose and mouth), cutaneous or ocular routes. Most laboratory studies on air pollutants have been limited to single air pollutants and very little research has been done on the complex mixture of compounds that exist in ambient air. Complex mixtures are further complicated by dynamic chemical reactions that occur after the emissions leave point sources. Exposure parameters are also important in the toxicity of air pollutants. Intermittent exposure of monkeys to ozone increased the adverse pulmonary effects. Superimposing spikes of 0.8 ppm nitrogen dioxide on a baseline of 0.2 ppm, as occurs on a calm winter day, increased the susceptibility of mice to bacteria-induced pneumonia. Sulfur dioxide at concentrations of 5 ppm increased pulmonary resistance by 39%. Sulfuric acid is the predominate acid particle in the atmosphere. Exposure for 1 h to > 200 micrograms sulfuric acid/m3 depressed bronchomucociliary clearance. Concentrations of 100 micrograms/m3 of photochemical products caused headaches and 510 micrograms/m3 produced cough and chest pain. For chemical interactions in dose response, nitrogen dioxide is synergistic with ozone and ammonium sulfate. When all 3 chemicals are used in mixture, the response was 340%. Atmospheric conditions, such as fog, can alter the toxicity of air pollutants. The dose response to a single chemical can be altered by chemical mixtures and pre-existing disease conditions. Understanding these relationships is important for establishing no observable adverse effect levels. Mechanisms for multiple chemical interactions are multifaceted. One chemical may interfere with the metabolism or detoxification of another. Others may interact at cell receptors. To understand the effects of multiple chemical interactions of air pollutants, there is a need for a blend of epidemiological, laboratory and field studies. Studies are expensive. In the rural agricultural settings, the economic and environmental health risks are high. Should field observations and chemical problems be used as "red flags" for action?