Sorption of hydrophobic contaminants to soils and subsurface solids is a significant limitation for the in situ chemical oxidation (ISCO) remediation of contaminated sites. A recently developed ISCO reagent, activated persulfate, was investigated for its potential to provide enhanced treatment of sorbed contaminants, a phenomenon that has previously been observed in catalyzed H(2)O(2) propagations (CHP; modified Fenton's reagent). Perchloroethylene (PCE) and hexachlorocyclopentadiene (HCCP) were sorbed to diatomaceous earth and treated with CHP, iron (II)-citrate-activated persulfate, and base-activated persulfate. Gas-purge desorption was used to measure the maximum natural rate of desorption of the compounds. Enhanced treatment of both sorbed probe compounds was observed in CHP reactions, with PCE and HCCP destruction occurring more rapidly than their respective rates of gas-purge desorption. However, probe compound loss in both formulations of activated persulfate was equal or less than the rates of gas-purge desorption, indicating that enhanced treatment of the sorbed contaminants did not occur in the persulfate reactions. Activated persulfate treatment is likely ineffective for hydrophobic compounds that are sorbed to soils and subsurface solids, and is probably more effective for compounds that are not limited by desorption.