Formation of hydroxyl radical (·OH) in illuminated surface waters contaminated with acidic mine drainage

Abstract

Formation rates and steady-state concentrations of hydroxyl radical (·OH) in illuminated surface water samples collected in west-central Indiana that receive acidic mine drainage runoff are reported. Formation rates for ·OH in samples were measured by the addition of 1 × 10−3 M benzene prior to illumination in order to effectively scavenge all of the ·OH formed, thereby yielding phenol. The ·OH formation rates were calculated from the measured phenol formation rates. Steady-state concentrations of ·OH were measured by the addition of 5 × 10−7 M nitrobenzene to the samples prior to illumination. Estimated sunlight ·OH formation rates range from 16 μM h−1 to 265 μM h−1. Estimated sunlight steady-state ·OH concentrations range from 6.7 × 10−15 to 4.0 × 10−12 M. Both the formation rates and steady-state concentrations for ·OH are thus two to three orders of magnitude higher than values reported in the literature for other sunlit surface water samples. Due to the very high rates of formation and steady-state concentrations for ·OH in these samples, we conclude that aqueous-phase reactions involving ·OH represent a significant pathway by which organic pollutants in illuminated surface waters receiving acidic mine drainage runoff may be consumed.