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Response to Comment on “Modeling Maximum Adsorption Capacities of Soot and Soot-like Materials for PAHs and PCBs” We appreciate the interest in our work demonstrated by Fetzer in his comment on our paper (1). We fully agree with him that one has to take great care when choosing a solvent for extraction of PAHs from pyrolytic materials because (i) different solvents may extract different amounts of PAHs and (ii) solvent extracts do not reflect bioavailable fractions by definition. In fact, in another recent paper (2), two of us have shown that large differences in PAH extraction recoveries from soot-like materials were observed among seven different solvents. It was proposed that differences in extraction recoveries originated from both differences in soot-swelling and PAH displacement capacities among solvents to release entrapped PAHs. Still, alkanes (as represented by an hexane/ acetone mixture) on average were able to extract 50-80% (relative to the amount extracted by the most optimal solvent) of PAHs present in soot-like materials. Therefore, we disagree with Fetzer where he suggests that an alkane could be the solvent of choice for the determination of available PAHs for risk assessment purposes. Also note that many studies have been published to demonstrate that solvent extraction does not mimic uptake by organisms. Other types of extraction that are more closely related to some aspects of the process of uptake by organisms do however offer the possibility for the determination of available PAHs (see, e.g., refs 3 and 4). We also doubt the theory of Fetzer that “PAHs adsorb more strongly than just due to van der Waal’s forces through the interactions of the π electrons with those of the partially graphitic structures in soots and other solid combustion products”. In fact, this may not be the case as it has been shown (5), and cited in ref 1, that adsorption of aromatic compounds onto carbon surfaces can be quantitatively described on the basis of van der Waals interactions only. We conclude that the comments of Fetzer do not affect the conclusions drawn in ref 1. His comments do, however,
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illustrate that further work is needed on both the molecular characterization of adsorption on carbon surfaces and on the morphological characteristics of carbon sorbents influencing this sorption. Such work will strengthen our understanding of adsorption onto carbon surfaces in soot-like materials, coals, active carbon, soils, and sediments.
Literature Cited (1) van Noort, P. C. M.; Jonker, M. T. O.; Koelmans, A. A. Environ. Sci. Technol. 2004, 38, 3305-3309. (2) Jonker, M. T. O.; Koelmans, A. A. Environ. Sci. Technol. 2002, 36, 4107-4113. (3) ten Hulscher, Th. E. M.; Postma, J.; den Besten, P. J.; Stroomberg, G. J.; Belfroid, A.; Wegener, J. W.; Faber, J. H.; van der Pol, J. J. C.; Hendriks, A. J.; van Noort, P. C. M. Environ. Toxicol. Chem. 2003, 10, 2258-2265. (4) Hawthorne, S. B.; Poppendieck, D. G.; Grabanski, C. B.; Loehr, R. C. Environ. Sci. Technol. 2002, 36, 4795-4803 (5) van Noort, P. C. M. Environ. Toxicol. Chem. 2003, 22, 11791188.
Paul C. M. van Noort* Department of Chemistry and Ecotoxicology Institute for Inland Water Management and Wastewater Treatment Lelystad, The Netherlands
Michiel T. O. Jonker Toxicology Division Institute for Risk Assessment Sciences Utrecht University Utrecht, The Netherlands
Albert A. Koelmans Aquatic Ecology and Water Quality Management Group Department of Environmental Sciences Wageningen University Wageningen, The Netherlands ES040521C
10.1021/es040521c CCC: $27.50
2004 American Chemical Society Published on Web 10/16/2004
