Complexation of iron by humic-like substances in lung tissue: role in coal workers' pneumoconiosis.

Deposition of coal dust in the lungs during the mining of this energy resource can cause an inappropriate fibrosis. Those characteristics of the coal responsible for lung injury are not known. The hypothesis was tested that 1) humic-like substances (HLS) in coal complex iron cations, which subsequently catalyze oxidant generation; and 2) the accumulation of this metal in the lungs of coal miners is associated with collagen deposition. In vitro measurements of ionizable ferric ion concentration ([Fe3+]) and oxidant generation by 10 standard coal dusts increased with the concentration of HLS. Dust mass, nonheme [Fe3+], and hydroxyproline concentrations in lung tissue were significantly higher in the lungs of coal miners, relative to matched controls. Although hydroxyproline concentrations increased with both dust mass and tissue nonheme [Fe3+], the association with the latter appeared greater. HLS in coal dusts sequestered in human lungs may be associated with injury as a result of their capacity to complex metals, which catalyze oxidant generation.