Correlations of soluble neprilysin (NEP) activity in subject sputum (N =11) with mining dust particulates (OS) and diesel exhaust (DE) exposure [concentrations, mg/m3 X time, min. (C X T)]. DE exposure was not corrected for pre-exposure levels in NEP activity (Data not shown). Cell-free NEP activity in induced sputum was measured spectrophotometrically. Personal particulate exposure was performed during OS mucking, using SKC aluminum cyclones in the subjects’ breathing zone attached to sampling pumps (SKC AirChek 2000, Eighty Four, PA). DE was collected on precleaned 37mm open-face quartz fiber filters (SKC, Eighty Four, PA) with MSA personal sampling pumps (Escort Elf, Pittsburgh, PA) and analyzed for elemental carbon according to NIOSH method 5040 by the Wisconsin State Hygiene Laboratory (Madison, WI). *Statistically significant.