962 Environmental Toxicology and Chemistry, Vol. 21, No. 5, pp. 962–971, 2002  2002 SETAC Printed in the USA 0730-7268/02 $9.00 + .00 PREDICTING BIOAVAILABILITY AND BIOACCUMULATION WITH IN VITRO DIGESTIVE FLUID EXTRACTION DONALD P. WESTON*² and K EITH A. MARUYA‡ ²University of California, Berkeley, Department of Integrative Biology, 3060 Valley Life Sciences Building, Berkeley, California 94720-3140, USA ‡Skidaway Institute of Oceanography, 10 Ocean Science Circle, Savannah, Georgia 31411, USA ( Received 24 May 2001; Accepted 21 October 2001) Abstract—Bioavailability of sediment-associated contaminants was assessed in parallel tests by means of a bivalve (Macoma nasuta) bioaccumulation assay and a novel in vitro digestive fluid extraction procedure. Digestive fluid was obtained from the deposit-feeding polychaete Arenicola brasiliensis and used to extract sediments from a U.S. Navy facility. Both the digestive fluid extraction and the bivalve bioaccumulation test identified Cd, Pb, high molecular weight polycyclic aromatic hydrocarbons (HPAHs), and polychlorinated biphenyls (PCBs) as the contaminants of concern; both procedures indicated that As, Cu, Hg, Ni, Zn, and low molecular weight polycyclic aromatic hydrocarbons were rarely, if ever, of concern. The only contaminant for which the techniques consistently differed was Cr, a result attributable to constraints on intestinal absorption of the metal by the bivalves. For Cd and Pb, the concentration attained in digestive fluid during a brief extraction was highly correlated with concentration attained in the bivalve after a 28-d exposure; correlation was marginal for HPAHs and was nonsignificant for PCBs. However, bulk sediment concentrations were equally good predictors of bioaccumulation because of minimal differences in bioavailability from the most contaminated sediments. In vitro contaminant extraction with the digestive fluid assay has potential as a screening tool to predict relative bioaccumulation risk, and has several advantages over traditional tests. Keywords—Bioaccumulation Bioavailability Macoma Risk assessment Digestive fluid extraction INTRODUCTION Assessment of the ecological risk posed by dredged ma- terial and other contaminated aquatic sediments often involves bioaccumulation testing. In freshwater sediments, the oligo- chaete Lumbriculus variegatus often is used, and in marine sediments, the bivalve Macoma nasuta or the polychaete Neanthes virens are often the test organisms. The long duration of the tests (often 28 d) and their extensive analytical require- ments often make bioaccumulation testing the most time-con- suming and costly component of sediment testing. In vitro digestive fluid extraction recently has been pro- posed as a good predictor of bioavailability for both organic compounds [1,2] and trace metals [3,4]. In this procedure, the digestive fluid of a deposit-feeding organism is obtained by dissection and then used as an extractant in in vitro incubation with the sediment of concern. The contaminant concentration attained in the digestive fluid is determined, and can be used to place a maximum limit on the bioavailable contaminant fraction via ingestion and digestion. Unlike conventional chemical extractions, which are intended to achieve complete recovery, digestive fluid extraction provides an estimate of the amount of contaminant solubilized in vivo by digestive pro- cesses and thus available for subsequent absorption and bio- accumulation. The fraction of contaminant extracted by di- gestive fluid is far less than that extracted by conventional organic solvents or strong acids, and far more than is extract- able by water [5]. In some instances, a weak acid extraction may yield comparable trace metal solubilization as digestive fluid, although mechanistically the two approaches have little in common because deposit-feeder digestive fluid is often near * To whom correspondence may be addressed: (dweston@uclink4.berkeley.edu). neutral pH [5]. Extraction with the digestive fluid of deposit- feeding polychaetes (Arenicola brasiliensis or Arenicola ma- rina) has been shown to be a good predictor of polycyclic aromatic hydrocarbon (PAH) bioaccumulation by the poly- chaete A. brasiliensis [1] and mercury bioaccumulation by the amphipod Leptocheirus plumulosus [3]. This study was designed to compare the relative bioavail- ability and bioaccumulation of contaminants from a variety of sediments by means of digestive fluid extraction with estimates of these parameters obtained from traditional 28-d bioaccu- mulation tests with M. nasuta. Thirteen in situ–contaminated estuarine sediments were assessed by both procedures, and the ability of digestive fluid extraction to predict contaminant up- take by M. nasuta was evaluated with respect to PAHs, po- lychlorinated biphenyls (PCBs), and eight trace metals. MATERIALS AND METHODS Sediment collection Sediments were collected in 1997 at the former Naval Air Station Alameda (now known as Alameda Point) in San Fran- cisco Bay (CA, USA), which was in the process of conversion to civilian use. Two areas of the base, Seaplane Lagoon and the Landfill Wetlands, were evaluated. Seaplane Lagoon is an embayment of San Francisco Bay and the location of two large outfalls that discharged industrial wastewater and storm runoff from the base [6]. The harbor areas in front of both outfalls were sampled, and designated as East Lagoon and West La- goon. The second area on the base, known as the Landfill Wetlands, was the site of past solid waste disposal but is now a wetland with no visible evidence of historical disposal. Sed- iments of three ponds at the site (designated as wetland ponds 1, 2, and 3) were sampled. Wetland pond 1 is connected to