ESR spin-trapping with 100 mM DMPO. The structure of DMPO adducts are drawn on the figure. Fenton generated (125 μM H2O2 & 25 μM Fe2+) •OH reacts with DMPO to form the DMPO-OH radical adduct (A). In the absence of •OH, ferric iron (100 μM) also produces the DMPO-OH radical adduct (B). Reaction of •OH with 30% ethanol results in the DMPO-CH(CH3)OH radical adduct (C). In the absence of •OH, but presence of 100 μM ferric iron and ethanol, DMPO-OCH2CH3 results (D). Pyrite (12.5 g/L) mixed with DMPO (without addition of H2O2) shows formation of DMPO-OH (E). The addition of ethanol reveals peak contributions from the DMPO-OH (marked with plus signs) and •OH-dependant DMPO-CH(CH3)OH radical adducts (marked with asterisks) (F). The experiment was conducted in the presence of O2. The raw ESR data are available as an additional file, Cohn_Fig 1 ESR data.XLS.