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Response to Comment on “Biodegradation of r-Pinene in Model Biofilms in Biofilters” We would like to thank Ronald Hites for his comment on our paper. We would agree with his assessment that the unknown in our samples is more likely to be 2,6-dimethyl-1,3,5,7octatetraene (also known as cosmen or cosmene). This compound was not in our database and we do agree that it does have a better match with our mass spectrum. Also, based on the papers he cited by Ozel et al. (1) and Veriotti and Sacks (2), the GC retention times appear to be in line with what we found with our unknown. Both these papers show cosmene with a significantly longer retention time than R-pinene which is similar to our results (pinene at about 3.5 min, unknown at about 8.5 min) on a similar (DB-5) column. While these are not definitive tests, they do support Ronald Hites’ comment. We should point out that we still think that this unknown is a biologically mediated transformation product that supports our basic model for biodegradation where a hydrophobic pollutant undergoes rapid conversion to a less volatile, more soluble compound that can then penetrate deeper into the biofilm (3). The unknown was never detected in the control with pinene only or in samples where complete degradation took place. Also, the compound elutes at a much later time on the DB-5 column than pinene and has a lower
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vapor pressure (0.79 vs 3.49 Torr for pinene estimated at 25 °C (4)) which suggests that it will have a lower air/water partition coefficient.
Literature Cited (1) Ozel, M. Z.; Gogus, F: Hamilton, J. F.; Lewis, A. C. The essential oil of Pistacia ver L. at various temperatures of direct thermal desorption using comprehensive gas chromatography coupled with time-of-flight mass spectrometry. Chromatographia 2004, 60, 79-83. (2) Veriotti, T.; Sacks, R. High-speed GC and GC/time-of-flight MS of lemon and lime oil samples. Anal. Chem. 2001, 73, 43954402. (3) Miller, M. J.; Allen, D. G. Biodegradation of R-pinene in model biofilms in biofilters. Environ. Sci. Technol. 2005, 39, 58565863. (4) Calculated using Advanced Chemistry Development (ACD/ Labs) Software V8.14 for Solaris (1994-2006 ACD/Labs), as cited in SciFinder Registry (www.cas.org) January 6, 2006.
D. Grant Allen and Martha J. Miller Department of Chemical Engineering and Applied Chemistry University of Toronto Toronto Ontario Canada ES060135Q
10.1021/es060135q CCC: $33.50
2006 American Chemical Society Published on Web 02/17/2006
