Bioavailability of iron from coal fly ash: Mechanisms of mobilization and of biological effects

Particulate air pollution contains iron that may be involved in the patholo gical effects after inhalation. This article reviews work demonstrating tha t ambient particulate samples (Standard Reference Material [SRM] 1648 and S RM 1649, from the National Institute of Science Science and Technology) con tain iron that can be mobilized from the particle in vitro and inside human lung epithelial (A549) cells. The mobilized iron can then catalyze the for mation of reactive oxygen species (ROS). Work is also reviewed on the gener ation and sire fractionation of coal fly ash (CFA) from three commercially important coal types, as well as size fractionation of three types of nonco mbustion particles. The availability of iron from these particles to A549 c ells was measured by citrate mobilization in vitro and induction of the iro n storage protein Ferritin in particle-treated cells. The amount of bioavai lable iron decreased with increasing particle size. The ability of particle s to induce synthesis of the proinflammatory cytokine interleukin-8 (IL-8) was also determined. As with the bioavailability of iron, there was an inve rse correlation with size. Further work showed that iron in CFA is responsi ble for IL-8 induction. Mossbauer spectroscopy of a CFA sample before and a fter desferrioxamine B treatment to remove bioavailable iron showed that th e bioavailable iron was associated with the glassy aluminosilicate fraction of the particle. In conclusion, this work shows that bioavailable iron is responsible for ROS production by SRMs and IL-8 induction by CFA in A549 ce lls. The source of this bioavailable iron in CFA is glassy aluminosilicates , which are found at higher levels in smaller sizes of CFA.