Commercially Available Chemicals That Mimic a Deposit Feeder’s ( Arenicola marina) Digestive Solubilization of Lipids IAN M. VOPARIL* ,† AND LAWRENCE M. MAYER Darling Marine Center, University of Maine, Walpole, Maine 04573 To develop a simple and cost-effective bioavailability test for sediment-bound contaminants, the solubilization strengths of mixtures of four commercially available surfactants and four proteins were compared to that of digestive fluids from a deposit-feeding benthic polychaete Arenicola marina. Initial tests indicated that sodium taurocholate, a vertebrate bile salt, was the most accurate mimic of A. marina gut fluids’ solubilization of individual polycyclic aromatic hydrocarbons (PAH). Further testing with nutritional lipids and other hydrophobic contaminants confirmed the similarities of these fluids. Bovine serum albumin (BSA) solubilization of PAH was the most efficient of all the proteins tested. A cocktail of sodium taurocholate and BSA was compared to A. marina’s solubilization of 12 PAH from four different contaminated sediments (from Boston, Charleston, Jacksonville, and San Diego harbors). The two solutions released most PAH to similar extents; 40 of 48 PAH-sediment combinations were released at amounts within a factor of 2 in cocktail and gut fluid solutions. Therefore, the cocktail may serve as a surrogate for real gut fluids and allow easier adoption of the in vitro incubation approach to bioavailability testing. Introduction In vitro incubations ofthe digestive fluids ofdeposit feeders with sediments can be used to quantify those contaminants that become digestively available to an animal during gut passage (1).After mixingsediment and digestive fluidsunder physiologically reasonable conditions, one quantifies the amount of contaminant desorbed into the fluid, based on the presumption that contaminants must first be solubilized bydigestivefluidsin orderto bebioavailable.Forhydrophobic compounds in general, solubilization in the gut is thought to be the limitingstep duringassimilation,asuptake into the cells lining the gut is a passive process and a function of concentration in the digestive fluid (2).Forveryhydrophobic organic compounds such as polycyclic aromatic hydrocar- bons (PAH; 3) and chlorinated hydrocarbons (4), gut fluid solubilization has thus far been shown to be equivalent to bioaccumulation. The gut fluid extraction approach has a number of advantagesoverconventionalbioaccumulation studiesusing live animals for sediment risk assessment (5). First, in vitro incubations can be consistently applied to sediments with a wider range of abiotic parameters (e.g., salinity, sediment grain size, total organic carbon) than could be tolerated by any single animal species for bioaccumulation studies. Second, bioaccumulation experiments often run for 28 days while in vitro incubations last only a few hours, with associated cost savings and faster data availability. However, the limited quantity of gut fluid available from most animals makes use of the in vitro technique difficult. Even when usinglarge polychaetes such as Arenicola m arina, usually only 1 mL of fluid is available per individual (6, 7). The small volume of gut fluid available from each animal becomes problematic when attempting to assay numerous samples as well as a threat to communities of animals compelled to support this endeavor. Therefore, we sought to develop a “cocktail” of com- mercially available substances that would mimic solubili- zation bydigestive agents in gut fluids.Such a cocktailwould offer the advantages of gut fluid incubations without the difficulties of animal collection and dissection. For the bioavailability of hydrophobic chemicals, important con- stituents of the cocktail are likely surfactants and proteins (7). For the nonselective, deposit-feeding polychaete A. marina (lugworm), surfactant micelles are responsible for 80-90% of the solubilization of the PAH benzo[a ]pyrene by gut fluids, with the rest likely due to globular proteins (8). A solution of sodium dodecyl sulfate (SDS) has been used to mimic bioaccumulation of two organic contaminants (hexachlorobenzene and tetrachlorobiphenyl)bytwo deposit feeders, Nereis succinea and Pectinaria gouldii (4). We modeled the cocktail after gut fluids from A. m arina because this animal appears to be a good general model for benthic macroinvertebrates. For example, A. m arina’s diges- tive mobilization of sedimentary contaminants occurs at concentrationsatthemedian amountsolubilized bygutfluids of a 17 other species of benthic invertebrates (7). Although individualanimalsoften showplasticityin digestive strength due to a number of factors including age (6) and diet (10), incorporation of such variability would be confounding at this early stage of cocktail development. Therefore, we compiled gut fluids from many individuals to create a gut fluid “standard”. Our approach was to start simply by testing gut fluid’s and commerciallyavailable compounds’abilitiesto mobilize individual PAH. The most successful surfactant mimic was challenged with an expanded set ofhydrophobiccompounds. Our study ultimately reached practical and environmental relevance with testing of four contaminated sediments collected from the field.In this paper,we refer to the collection ofhydrophobiccompoundsstudied as“lipids”,in accordance with the operational definition of this group of compounds (11). Materials and Methods Arenicola marina Gut Fluids. A. m arina (Linnaeus, 1758) (lugworm) individuals were collected from sandflats near Lubec, ME, in July 1999. Animals were stored in seawater for up to 4 h, and mid-gut fluids were removed by dissection. Fluids from the mid-gut have maximalenzyme activities and surfactant concentration (6).Individuals’fluidswere pooled, passed through a 0.45 μm PTFE membrane filter, decanted into plastic containers, and stored at -80 °C until use. The surfactancy of gut fluid was measured using the contact angle technique (6). The critical micelle dilution (CMD) was 15% for this fluid, which indicates a surfactant concentration of approximately 13.3 mM in the original gut *Correspondingauthor phone: (831)459-1533,fax: (831)459-4882; e-mail: ivoparil@es.ucsc.edu. † Present address: Ocean Sciences Dept., University ofCalifornia Santa Cruz, Santa Cruz, CA 95064. Environ. Sci. Technol. 2004, 38, 4334-4339 4334 9 ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 38, NO. 16, 2004 10.1021/es049506y CCC: $27.50  2004 American Chemical Society Published on Web 07/09/2004