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 ϫ 10 Ϫ3 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 ϫ 10 Ϫ7 M nitrobenzene to the samples prior to illumination. Estimated sunlight • OH formation rates range from 16 M h Ϫ1 to 265 M h Ϫ1 . Estimated sunlight steady-state • OH concentrations range from 6.7 ϫ 10 Ϫ15 to 4.0 ϫ 10 Ϫ12 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.

Role of the photo-Fenton reaction in the production of hydroxyl radicals and photobleaching of colored dissolved organic matter in a coastal river of the southeastern United States

“…∑ OH production in the Satilla River water (4 x 10 -10 M s -1 ) agrees with that found for other similar waters from the southeastern US, the Ogeechee River (White, 2000) and the Everglades . The ∑ OH production rate in the New Jersey Pine Barrens sample was very high (10 -9 M s -1 ), approaching that observed in waters contaminated with acid mine drainage (Allen et al, 1996). ∑ OH pro- 1.0 ± 0.2 ¥ 10 -3 6.5 ¥ 10 -4 120 1.2 ¥ 10 -3 6.8 ¥ 10 -4 410 E. M. White, P. P. Vaughan and R. G. Zepp Photo-Fenton produced ∑OH and CDOM photobleaching duction in Mississippi River Plume water was on the same order of magnitude (10 -11 M s -1 ) as waters from Biscayne Bay and Vineyard Sound as well as various lakes (Haag and Hoigné, 1985;Zepp et al, 1987;Mabury, 1993).…”

“…Our findings suggest that this mechanism for ∑ OH production also is important in other iron-rich natural waters that are mildly acidic. For example, waters which receive acid mine drainage will likely have high steady-state ∑ OH concentrations due to photo-Fenton production (Allen et al, 1996;McKnight et al, 1988). In waters with high rates of ∑ OH photoproduction it seems likely that ∑ OH may play a significant role in the photoreactions of CDOM and aquatic pollutants.…”

Indirect Photochemistry in Sunlit Surface Waters: Photoinduced Production of Reactive Transient Species

“…OH] −1 is very high. Furthermore, the pH trend of the ⋅ OH yields in the Fenton and photo‐Fenton reactions partially explains (together with the HNO 2 /NO 2 − equilibrium) the considerable enhancement of ⋅ OH photogeneration in acidified surface waters 128. 129…”

A Model to Predict the Steady‐State Concentration of Hydroxyl Radicals in the Surface Layer of Natural Waters

“…23,25 The degradation kinetics of many dissolved molecules can be influenced by • OH, and the relevant half-life time would depend on [ • OH] and the second-order rate constant k OH for reaction between the molecule and • OH. [33][34][35] It is relatively easy to derive the relationship between the different quantities, but it should be considered that the model described here is valid for 22 W m − 2 sunlight UV intensity, while outdoor intensity is variable. Considering that [ • OH] is directly proportional to the irradiation intensity, 22 it was possible to derive that 9.5 h irradiation under 22 W m − 2 sunlight UV would be equivalent to a summer sunny day (15 July, 45°N latitude).…”