MASS TRANSFER LIMITATIONS ON BIOAVAILABILITY OF PAHS FROM CONTAMINATED ESTUARINE SEDIMENTS David S. Kosson*, Dept. of Civil and Environmental Engineering, Vanderbilt University, Nashville, TN Leslie M. Shor, Dept. of Chemical and Biochemical Engineering, 2 Rutgers University, Piscataway, NJ Karl J. Rockne, Dept. of Chemical and Biochemical Engineering, 2 Rutgers University, Piscataway, NJ Wenhsin Liang, BIOTECH Center, Rutgers University, New Brunswick, NJ Gary L. Taghon, Institute of Marine and Coastal Sciences, Rutgers University, New Brunswick, NJ Lily Y. Young, BIOTECH Center, Rutgers University, New Brunswick, NJ *speaker INTRODUCTION Limitations on the rate and extent of biodegradation of polycyclic aromatic hydrocarbons (PAHs) present in sediments are frequently attributed to slow desorption from the solid phase. However, partly because natural systems are so complex, few studies have been able to isolate and establish the relative contributions from each of several proposed mechanisms. Several recent studies have included model sorbents dosed with contaminants and aged for various periods of time in desorption and bioavailability experiments. (Calvillo & Alexander 1996; Cornelissen et al. 1998; Farrel & Reinhard 1994a; Farrel & Reinhard 1994b; Guerin & Boyd 1997; Nam & Alexander 1998; Scow & Alexander 1992). While these studies have utilized simplified conditions to uncover important trends, they are potentially limited by the difficulty in applying the results to natural soil or sediment systems and/or because of the shortcomings in trying to accurately reproduce field-aged behavior using laboratory-amended materials (Hatzinger & Alexander 1995; Pignatello et al. 1993). The alternative is to find other ways to isolate competing mechanisms in field-aged soil or sediment. In this study, field-aged PAH-contaminated sediments from two sites were divided into 36 different portions by size- and density-fractionation and extensively characterized for physical and chemical parameters likely to affect desorption. Rate and extent of PAH desorption and equilibrium partition coefficients were measured for many of the fractions. These results will be compared to ongoing independent PAH biodegradation experiments using similar sediment fractions to more effectively identify the mechanisms controlling slow desorption and limiting bioavailability. EXPERIMENTAL Two sampling locations in the New York Harbor Estuary were chosen because they possess vastly different physical, chemical, and biological characteristics. Piles Creek, a tributary of Arthur Kill, runs through a marshy area with abundant emergent vegetation. Newtown Creek is an industrial waterway in Queens NY. Both sites had been exposed to PAHs for decades. The sediments were fractionated into 5 size classes (>500 um, 500-300 um, 300-125 um, 125-63 um, and <63um) by wet sieving in clean seawater. The low- and high-density fractions of each of these samples plus whole sediment were separated by equilibrium flotation/settling in a saturated CsCl (p=1.8 g/ml) (see Rockne et al. 1999). The size- and density-separation resulted in 18 fractions from each site, for a total of 36 sub- samples. Chemical Characterization. On each fraction, total organic carbon was measured using a Carlo Erba elemental analyzer as described previously (Mayer et al. 1993). PAHs were extracted from all sediment fractions using a novel hot acetonitrile extraction procedure. Sediments were dewatered by centrifugation (8000g) and extracted in sealed Teflon Oak Ridge centrifuge tubes with boiling acetonitrile (85° C, 120 min) in an ultrasonic bath. This procedure was verified to provide high extraction efficiency with a NIST PAH-contaminated sediment standard. PAHs in the acetonitrile extract were analyzed by HPLC with fluorescence and photodiode array detection/identification.