Context: There have been no animal studies of the health effects of repeated inhalation of mixtures representing downwind pollution from coal combustion. Environmental exposures typically follow atmospheric processing and mixing with pollutants from other sources.
Objective: This was the fourth study by the National Environmental Respiratory Center to create a database for responses of animal models to combustion-derived pollutant mixtures, to identify causal pollutants-regardless of source.
Methods: F344 and SHR rats and A/J, C57BL/6, and BALB/c mice were exposed 6 h/day 7 days/week for 1 week to 6 months to three concentrations of a mixture simulating key components of "downwind" coal combustion emissions, to the highest concentration filtered to remove particulate matter (PM), or to clean air. Emissions from low-sulfur subbituminous coal were modified to create a mixture recommended by an expert workshop. Sulfur dioxide, nitrogen oxides, and PM were the dominant components. Nonanimal-derived PM mass concentrations of nominally 0, 100, 300, and 1000 µg/m(3) were mostly partially neutralized sulfate.
Results: Only 17 of 270 species-gender-time-outcome comparisons were significantly affected by exposure; some models showed no effects. There was strong evidence that PM participated meaningfully in only three responses.
Conclusion: On a total mass or PM mass basis, this mixture was less toxic overall than diesel and gasoline exhausts or wood smoke. The largely sulfate PM contributed to few effects and was the sole cause of none. The study did not allow identification of causal pollutants, but the potential role of NOx in some effects is suggested by the literature.