Passive Samplers Provide a Better Prediction of PAH Bioaccumulation in Earthworms and Plant Roots than Exhaustive, Mild Solvent, and Cyclodextrin Extractions. Jose L. Gomez-Eyles, †,‡, * Michiel T. O. Jonker, § Mark E. Hodson, † and Chris D. Collins † † School of Human and Environmental Sciences, Soil Research Centre, University of Reading, Reading, RG6 6DW, Berkshire, United Kingdom ‡ Department of Chemical, Biochemical and Environmental Engineering, University of Maryland Baltimore County, 1000 Hilltop Circle, Baltimore, Maryland 21250, United States § Institute for Risk Assessment Sciences, Utrecht University, P.O Box 80177, 3508 TD Utrecht, The Netherlands * S Supporting Information ABSTRACT: A number of extraction methods have been developed to assess polycyclic aromatic hydrocarbon (PAH) bioavailability in soils. As these methods are rarely tested in a comparative manner, against different test organisms, and using field-contaminated soils, it is unclear which method gives the most accurate measure of the actual soil ecosystem exposure. In this study, PAH bioavailability was assessed in ten field-contaminated soils by using exhaustive acetone/hexane extractions, mild solvent (butanol) extractions, cyclodextrin extractions, and two passive sampling methods; solid phase micro extraction (SPME) and polyoxymethylene solid phase extraction (POM-SPE). Results were compared to actual PAH bioaccumulation in earthworms (Eisenia fetida) and rye grass (Lolium multif lorum) roots. Exhaustive, mild solvent and cyclodextrin extractions consistently overpredicted biotic concentrations by a factor of 10-10 000 and therefore seem inappropriate for predicting PAH bioaccumulation in field contaminated soils. In contrast, passive samplers generally predicted PAH concentrations in earthworms within a factor of 10, although correlations between predicted and measured concentrations were considerably scattered. The same applied to the plant data, where passive samplers also tended to underpredict root concentrations. These results indicate the potential of passive samplers to predict PAH bioaccumulation, yet call for comparative studies between passive samplers and further research on plant bioavailability. ■ INTRODUCTION Polycyclic aromatic hydrocarbons (PAHs) are a class of widely distributed organic pollutants, which are ubiquitous in soils in low (μg/kg) concentrations, but which can also exist locally in very high (mg-g/kg) levels. PAHs are generally released into the environment as byproducts of combustion and pyrolysis processes (pyrogenic PAHs) or via spills of petroleum products, like diesel or oil (petrogenic PAHs). Pyrogenic PAHs are usually emitted within a matrix of tar, pitch, or black carbon-like products such as coke or soot, while petrogenic PAHs are released within a nonaqueous phase liquid (NAPL) matrix. These matrixes have been shown to provide strong sorption domains for PAHs, 1-4 and therefore have the potential to greatly reduce their bioavailability to soil organisms. 5 Measuring the total concentration of PAHs in soils using exhaustive solvent extractions and predicting risks using generic organic carbon-normalized sorption coefficients as is common practice in most countries, can therefore lead to over- conservative risk assessments. 6,7 This may result in unnecessary remediations or hinder the redevelopment of brownfield sites. Over the past decade, several extraction methods have been developed to address this issue by attempting to measure only bioavailable PAH concentrations. These methods include mild solvent extractions, 8,9 hydroxypropyl-β-cyclodextrin (HPCD) extractions, 10 Tenax extractions, 11 solid phase micro extractions (SPME), 6,7 polyoxymethylene solid phase extractions (POM- SPE), 7 supercritical fluid extractions (SFE), 5 and persulphate oxidation. 12 A number of studies have demonstrated how some of these methods provide a prediction of PAH concentration that is closer to what is actually bioavailable than traditional exhaustive extractions. Most studies so far have focused on testing a single chemical-analytical method, which was usually evaluated by comparing how well the method approximated or correlated with the amount of PAHs degraded by micro- organisms 10,12 or the PAH concentration accumulated in a single organism, like earthworms. 5,6 Also most studies were Received: October 3, 2011 Revised: December 5, 2011 Accepted: December 13, 2011 Published: December 13, 2011 Article pubs.acs.org/est © 2011 American Chemical Society 962 dx.doi.org/10.1021/es203499m | Environ. Sci. Technol. 2012, 46, 962-969