Dissolved organic matter inhibition of sonochemical degradation of aqueous polycyclic aromatic hydrocarbons

Sonochemical degradation of aqueous polycyclic aromatic hydrocarbons (PAHs) was found to be rapid in the absence of other dissolved compounds (k = 0.006-0.015 s-1). In the presence of 20 mg Cl-1 fulvic acid, first-order PAH degradation rate constants decreased from 2.3- to 3.7-fold. Similar results were obtained with added benzoic acid, a crude analog for fulvic acid. In natural waters, PAH degradation was almost completely inhibited. Analysis of the kinetic behavior and reaction products indicates that PAHs are most likely degraded through a radical cation mechanism. Hydroxyl radical appeared to play an insignificant role in the degradation. Inhibited degradation was probably the result of either altered cavitation processes or isolation of the PAH away from cavitation sites.