Rates of Hydroxyl Radical Production from Transition Metals and Quinones in a Surrogate Lung Fluid

Hydroxyl radical ((OH)-O-center dot) is the most reactive, and perhaps most detrimental to health, of the reactive oxygen species. (OH)-O-center dot production in lungs following inhalation of particulate matter (PM) can result from redox-active chemicals, including iron and copper, but the relative importance of these species is unknown. This work investigates (OH)-O-center dot production from iron, copper, and quinones, both individually and in mixtures at atmospherically relevant concentrations. Iron, copper, and three of the four quinones (1,2-naphthoquinone, phenanthrenequinone and 1,4-naphthoquinone) produce (OH)-O-center dot. Mixtures of copper or quinones with iron synergistically produce (OH)-O-center dot at a rate 20-130% higher than the sum of the rates of the individual redox-active species. We developed a regression equation from 20 mixtures to predict the rate of (OH)-O-center dot production from the particle composition. For typical PM compositions, iron and copper account for most (OH)-O-center dot production, whereas quinones are a minor source, although they can contribute if present at very high concentrations. This work shows that Cu contributes significantly to (OH)-O-center dot production in ambient PM; other work has shown that Cu appears to be the primary driver of HOOH production and dithiothreitol (DTT) loss in ambient PM extracts. Taken together, these results indicate that copper appears to be the most important individual contributor to direct oxidant production from inhaled PM.