Cytotoxicity of size-density fractionated coal fly ash in rat alveolar macrophages cultured in vitro.

The cytotoxicity of coal fly ash particles was investigated in rat alveolar macrophages cultured in vitro. Fly ash particles of a similar diameter (1-5 mum) were selected and then separated into five groups with respect to density (i.e. <1.6, 1.6-2.0, 2.0-2.4, 2.4-2.8 and >2.8 g/cm(3)). The exclusion of trypan blue and the extracellular release of lactate dehydrogenase were used as indicators of cell viability. The fraction of fly ash particles with the highest density (>2.8 g/m(3)) was most cytotoxic. The degree of cytotoxicity appeared to be correlated with the amount of particles taken up by macrophages as well as with their heavy metal concentrations. Morphological observation of the surface of the macrophages by scanning electron microscopy revealed a decrease in the number of filopodia and microvilli and an enhancement of the ruffled membrane. These morphological changes became more obvious with increasing concentrations of fly ash particles, but there was no characteristic change specific to each fraction of fly ash.