Hydroxyl radical formation from bacteria assisted Fenton chemistry at neutral pH under environmentally relevant conditions

Dark Fenton chemistry is an important source of hydroxyl radicals (OH center dot) in natural waters in the absence of sunlight. Hydroxyl radical production by this process is very slow in many bodies of water, owing to slow reduction and low solubility of Fe III at neutral and near-neutral pH. We have investigated the effects of the iron-reducing bacteria Shewanella oneidensis (SO) on OH center dot production rates from Fenton chemistry at environmentally relevant hydrogen peroxide (H2O2) and iron concentrations at neutral pH. In the presence of 2.0 x 10(-4) M H2O2, OH center dot production rates increased from 1.3 x 10(-10) to 2.0(-10) x 10(-10) Ms-1 in the presence of 7.0 x 10(6) cells mL(-1) SO when iron (at a concentration of 100 mu M) was in the form of Fe-II, and from 3.6 x 10(-11) to 2.2 x 10(-10) M s(-1) when iron was in the form of Fe-III. This represents rate increases of factors of 1.5 and 6 respectively. We measured OH center dot production rates at a range of H2O2 concentrations and SO cell densities. Production rates depended linearly on both variables. We also demonstrate that bacteria-assisted Fenton chemistry can result in rapid degradation of aromatic pollutants such as anthracene. Our results suggest that iron-reducing bacteria such as SO may be important contributors to radical formation in dark natural waters.