Inhibited hydroxyl radical degradation of aromatic hydrocarbons in the presence of dissolved fulvic acid

Degradation of aqueous aromatic compounds with hydroxyl radical produced by Fenton chemistry is inhibited by dissolved fulvic acid. The degree of inhibition is significantly greater than that expected, based on a simple model in which the fraction of aromatic compound bound to fulvic acid is considered to be unreactive. The reaction of three aromatic compounds (phenol, fluorene, and phenanthrene) with hydroxyl radical was monitored as a function of Suwannee River fulvic acid concentration. Steady state hydroxyl radical concentration was produced by Fenton chemistry (H2O2+Fe2+→Fe3++HO−+HO•) with continuous addition of hydrogen peroxide to Fe2+ solutions. Separation of the hydroxyl radical formation sites from the location of the aromatic compound is believed to be the reason for the observed reduction in rate constants, indicating that these systems are heterogeneous on a microenvironmental scale. The larger than expected inhibition of Fenton degradation by fulvic acid indicates that natural organic matter presents a significant impediment to remediation of pollutants in natural waters and soils.