827 Research Article Received: 8 December 2008 Revised: 1 February 2009 Accepted: 2 February 2009 Published online in Wiley Interscience: 6 April 2009 (www.interscience.wiley.com) DOI 10.1002/jctb.2160 Effect of vegetable oil addition on bioaccessibility and biodegradation of polycyclic aromatic hydrocarbons in historically contaminated soils Kerstin E Scherr, a* Marion Hasinger, a Philipp Mayer b and Andreas P Loibner a Abstract BACKGROUND: Bioaccessibility is often the limiting factor for the biodegradation of polycyclic aromatic hydrocarbons (PAH) in soils. The present study explores the potential of amending canola oil, an economically and ecologically attractive soil additive, for the enhancement of bioaccessibility and, in consequence, biodegradation of PAH in historically contaminated, bioaccessibility limited soils. RESULTS: The amendment of canola oil (1% and 5%, w/w) to contaminated soils increased the bioaccessibility and the subsequent biodegradation of PAH with up to four rings. Residual concentrations of pyrene and fluoranthene in oil-treated soils were 38 – 53% lower compared to the unamended tests. The continuous removal of bioaccessible PAH with a passive sampling system confirmed that oil amendment indeed increased bioaccessibility, leading to a lower non-accessible PAH fraction. Canola oil amendment did, by contrast, not increase the bioaccessibility of high molecular weight PAH, likely due to their strong binding to soil organic carbon compounds. CONCLUSION: Canola oil can be used efficiently in low concentrations to render PAH up to four rings accessible for biodegradation in historically contaminated soils. Contaminants remaining in soil after treatment may pose a significantly lowered environmental risk, as is indicated by the lack of mobilisation by a solubilising agent such as canola oil. c  2009 Society of Chemical Industry Keywords: bioremediation; soil; polycyclic aromatic hydrocarbons; bioaccessibility; canola oil; passive sampling INTRODUCTION Polycyclic aromatic hydrocarbons (PAH) are a widely distributed class of hydrophobic organic contaminants in the environment. Owing to the mutagenic and carcinogenic effect that is assigned particularly to high molecular weight congeners, 1,2 PAH pose a serious threat to environmental receptors and human health. In the 1980s, 16 polycyclic aromatic compounds were listed as priority pollutants by the US Environmental Protection Agency (16 EPA PAH 3,4 ). The considerable impact of PAH as environmental contaminants has led to the development of sophisticated remediation technologies for the clean-up of contaminated soils and sediments, such as bioremediation, which is based on supporting the natural capability of microorganisms to metabolise organic contaminants. The recalcitrance of PAH to biological degradation processes increases with increasing ring number. 5–7 However, the extent of PAH biodegradation and resulting residual concentrations in the subsurface is strongly dependent on, besides microbial factors, PAH bioavailability, which is often the delimiting parameter for PAH biodegradation in the subsurface. Numerous methodical and systematic approaches for the determination of contaminant bioavailability have been published. 8–13 Recently, the distinction of two incommensurable aspects of bioavailability has been proposed. 14 The chemical activity of a compound, on the one hand, provides a measure for the chemical’s potential to undergo spontaneous physicochemical processes such as partitioning and diffusion, and can be precisely defined. 15 The close relationship between the chemical activity and the toxicity of PAH to small soil invertebrates has recently been demonstrated. 16 The bioaccessible quantity of a contaminant, on the other hand, describes the quantity of the contaminant that can be released from the soil and become available for biological processes, such as uptake or biodegradation. 14 Bioaccessibility will always remain operationally defined, since it depends on ∗ Correspondence to: Kerstin E Scherr, University of Natural Resources and Applied Life Sciences, Department of Agrobiotechnology, Institute of En- vironmental Biotechnology, Konrad Lorenz Strasse 20, 3430 Tulln, Austria. E-mail: kerstin.scherr@boku.ac.at a University of Natural Resources and Applied Life Sciences, Department of Agrobiotechnology, Institute of Environmental Biotechnology, Konrad Lorenz Strasse 20, 3430 Tulln, Austria b National Environmental Research Institute, Aarhus University, Frederiksborgvej 399, DK-4000 Roskilde, Denmark J Chem Technol Biotechnol 2009; 84: 827–835 www.soci.org c  2009 Society of Chemical Industry