Mobilization of iron from coal fly ash was dependent upon the particle size and the source of coal

Particulate air pollution, including coal fly ash, contains iron, and some of the pathological effects after inhalation may he due to reactive oxygen species produced by iron-catalyzed reactions. The objective of this study w as to determine whether iron, present in coal fly ash, was mobilized, leadi ng to ferritin induction in human airway epithelial cells, and whether the size of the particles affected the amount of iron mobilized. Three types of coal were used to generate the three size fractions of fly ash collected. The Utah coal fly ash was generated from a bituminous b coal, the Illinois coal fly ash from a bituminous c coal, and the North Dakota coal ny ash fro m a lignite a coal, Three size fractions were studied to compare the amount of iron mobilized in human airway epithelial (A549) cells and by citrate i n cell-free suspensions. The size fractions selected were fine (<2.5 mu m) and coarse (2.5-10 mu m) components of PM10, airborne particulate matter < 1.0 mu m in diameter, and the fraction greater than 10 mu m. Coal fly ash s amples were incubated with 1 mM citrate to determine if iron associated wit h coal fly ash could be mobilized. Iron was mobilized by citrate from all t hree size fractions of all three coal types to levels as high as 56.7 nmol of Fe/mg of coal fly ash after 24 h, With all three coal types, more iron w as mobilized by citrate from the <2.5 mu m fraction than from the >2.5 mu m fractions, Further, the mobilized iron was in the Fe(III) form. Tn determi ne if iron associated with the coal fly ash could be mobilized by A549 cell s, cells were treated with coal fly ash, and the amount of the iron storage protein ferritin was determined after 24 h. Ferritin levels were increased by as much as 11.9-fold in cells treated with coal fly ash. With two of th e three types of coal studied, more ferritin was induced in cells treated w ith the <2.5 mu m fraction than with the >2.5 mu m fractions. Further, inhi bition of the endocytosis of the coal fly ash by the cells resulted In ferr itin levels that were near that of the untreated cells, suggesting that iro n was mobilized intracellularly, not in the culture medium. The results of this study suggest that differences in particle size and speciation of iron may affect the release of iron in human airway epithelial cells.