Health effects of subchronic inhalation exposure to simulated downwind coal combustion emissions

Abstract

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/m³ were mostly partially neutralized sulfate.

Results: Only17 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.

Keywords::

• Air pollution
• coal
• particulate matter
• sulfate
• sulfur dioxide
• nitrogen dioxide
• nitrogen oxides
• lung
• respiratory
• bronchoalveolar lavage
• alveolar macrophages
• micronucleus
• clotting factors
• bacterial clearance
• respiratory allergy
• systemic immunity

Acknowledgments

The authors thank the many members of the LRRI technical staff who developed and operated the exposure system, maintained the animals, and performed the biological measurements. The coal was obtained and processed by the Energy and Environmental Research Center of the University of North Dakota.

Declaration of interest

The authors report no conflicts of interest. As noted above, this research was funded jointly by multiple government and industry sponsors. This work was supported by the National Environmental Respiratory Center, which was funded by numerous industry, state, and federal sponsors, including the U.S. Environmental Protection Agency (Office of Research and Development), U.S. Department of Energy (Office of Freedom Car and Vehicle Technologies and National Energy Technology Laboratory). Decisions and approvals regarding experimental strategy and design were vested in an advisory committee independent from sponsorship. Neither the committee nor the sponsors reviewed this manuscript before submission. This manuscript has not been reviewed by any sponsor and is not intended to represent the views or policies of any sponsor.