The dissolution of naphthalene, phenanthrene, and pyrene from viscous organic phases into water was studied in continuous-flow systems for time periods ranging from several months to more than 1 year. By selecting nonaqueous phases ranging fromlow viscosity to semisolid, i.e., from a light lubricating oil to paraffin, the governance of mass transfer was shown to vary from water phase control to nonaqueous phase control. An advancing depleted-zone model is proposed to explain the dissolution ofPAHs from a viscous organic phase wherein the formation of a depleted zone within the organic phase increases the organic phase resistance to the dissolution of PAHs. The experimental data suggest the formation of a depleted zone within the organic phasefor systems comprising a highviscosity oil (~1000 cP at 4O ℃), petrolatum (petroleum jelly), and paraffin. Organic phase resistance to naphthalene dissolution became dominant over aqueous phase resistance after flushing for several days. Such effectswere not evident for low viscosity lubricating oil (86 cP at 40 ℃). The transition from aqueous-phase dissolution control to nonaqueous-phase dissolution control appears predictable, and this provides a more rational framework to assess longterm releaseof HOCs from viscous nonaqueous phase liquids and semisolids.
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