STUDIES OF THE CHRONIC INHALATION OF COAL FLY ASH BY RATS

Abstract Respiratory disease-free rats were exposed in two experiments to respirable (mass median aerodynamic diameter MMAD about 2 μ) aerosols of size-classified power plant fly ash at average concentrations of up to 4.2 mg m -3 for 8 h per day for up to 180 consecutive days. The aerosols were characterized with respect to both physical and chemical properties. Immediately after exposure, the animals were evaluated biochemically, morphologically and with other sensitive biological tests to detect effects associated with fly ash inhalation when compared with unexposed controls. Lung burdens of up to 4 mg of ash were found. Macrophages lavaged from lungs of exposed rats were more numerous and yielded more progenitor cell colonies in culture (at the 10% confidence level based on the Mann-Whitney rank-sum test) than from controls. Tracheal mucous glycoprotein secretion was decreased at 7,50 and 90 days of exposure and increased at 180 days. Clumping of fly ash in cells in the lungs was observed. There were no apparent untoward health effects from inhaled fly ash, since the observed differences between exposed and control rats did not constitute an adverse response.