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Response to Comment on “Reactions of Polynuclear Aromatic Hydrocarbons on Soil” SIR: Kopinke and Mackenzie have quite correctly identified an important variable in any polymerization reaction, namely, the mobility of the monomeric reactants. As stated in the paper (1), our experiments were intended to study the solventrich conditions that would prevail after a spill on surface soil. Under such spill conditions, polynuclear aromatic hydrocarbons (PAHs) are mixed with a variety of other components in a liquid organic phase. With time, this mixture can undergo many compositional changes, including evaporation, oxidation, and biodegradation. The mobility of PAHs for reactions, such as polymerization, would tend to change with time. Clearly, additional studies would be required to evaluate the change in reaction rate with changing composition of the nonaqueous phase liquid. Kopinke and Mackenzie suggest that spiking of pure compounds onto soil without solvent is representative of the situation in the environment. This assertion is true in some cases, but not in the case of a spill of liquid on soil, which
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was the intent of our study. The diffusivity of anthracene in dichloromethane will differ from anthracene oil or a more weathered NAPL phase, but diffusivity will be far higher than in a spiked soil where anthracene mainly interacts with the soil organic matter. We are delighted at the additional observations of Kopinke and Mackenzie on reactions during low-temperature treatment. Their elegant approach to demonstrating the importance of redox reactions and radical or radical-ion species is a most welcome support for our proposed mechanism.
Literature Cited (1) Karimi-Lotfabad, S.; Pickard, M. A.; Gray, M. R. Environ. Sci. Technol. 1996, 30, 1145-1151.
S. Karimi-Lotfabad, M. A. Pickard, and M. R. Gray* University of Alberta Edmonton, Alberta, Canada T6G 2E9 ES962015W
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