Abstract-The ability to predict accumulation levels of sediment-sorbed hydrophobic organic contaminants (HOCs) by depositfeeding organisms based on sediment concentrations is limited in part by an incomplete understanding of the chemistry that controls assimilation efficiency. This study was designed to test the hypothesis that desorption is an important process that controls the bioavailability of HOCs to deposit-feeding organisms; we planned to do so by conducting desorption and bioavailability experiments with field-contaminated sediments collected from New York Harbor, New York, USA. Three classes of organic contaminants, polychlorinated biphenyls (PCBs), polycyclic aromatic hydrocarbons (PAHs), and linear alkylbenzenes (LABs) were studied. In order to address the effects of contaminant aging, we compared the contaminant desorption rates from sediments collected from surface and at depth in an area of known high-sediment accumulation to retarded intraparticle model predictions. Measured desorption rates of the LABs and the most hydrophobic PCBs compare well with model predictions. However, the PAH and less hydrophobic PCB desorption rates range from one to four orders of magnitude slower than model predictions. We postulate that these compounds are present in a resistant sedimentary phase and may represent only a small fraction of what was originally sorbed. The fraction of PCBs, PAHs, and LABs desorbed after 48 h correlate well with measured biota-sediment factors (BSFs) in Yoldia limatula that were exposed to the same sediments, indicating that desorption rate-limited assimilation. Several studies have related field BSFs with log K ow and have observed a maximum at intermediate K ow s (ϳ6.0-6.5). This maximum may be due to predictably slow desorption of high-K ow compounds and may be lower than predicted rates and extent of desorption of the low-K ow compounds because of association with resistant phases.

Solubilization of sediment-bound hydrophobic contaminants (HOCs) by gut fluids of deposit-feeding polychaetes greatly exceeds solubilization by seawater. We present evidence that digestive surfactants exert a central role in HOC desorption, and that the degree of in vitro solubilization by gut fluids is an excellent predictor of HOC absorption efficiency (AE) by the respective worm species. We compared in vitro solubilization of sediment-bound 14 C-hexachlorobenzene (HCB) and 14 C-tetrachlorobiphenyl (TCBP) by gut fluids of 2 deposit-feeding polychaete species, Nereis (Neanthes) succinea and Pectinaria (Cistenides) gouldii, to AEs measured in live worms by pulsechase methodology. N. succinea desorbed 72% HCB and 79% TCBP in vitro (during 6 h incubations), and absorbed both compounds with 73% efficiency, while P. gouldii desorbed only 37% HCB in 6 h, and analogously absorbed only 37% HCB. Higher desorption and absorption efficiencies of N. succinea were accompanied by greater gut-fluid surfactancy and higher micelle concentration (determined by drop contact angle) compared to P. gouldii. Calibration of desorption efficiencies with a synthetic surfactant, sodium dodecyl sulfate (SDS), showed that N. succinea gut fluid desorbed a similar amount of HOC as a 1% (ca 3.5 mM) SDS solution, whereas P. gouldii gut fluid was equivalent to a 0.25% (ca 0.9 mM) SDS solution. Detailed analysis of the kinetics of HOC desorption (after 1, 45 and 360 min) showed that gut fluids from both polychaetes desorbed more than two-thirds of the bioavailable HOC within the first minute, suggesting that digestive desorption occurs rapidly and that gutresidence time has only minor influence on the degree of desorption or absorption of sediment-bound HOCs.

The ability to predict accumulation levels of sediment‐sorbed hydrophobic organic contaminants (HOCs) by depositfeeding organisms based on sediment concentrations is limited in part by an incomplete understanding of the chemistry that controls assimilation efficiency. This study was designed to test the hypothesis that desorption is an important process that controls the bioavailability of HOCs to deposit‐feeding organisms; we planned to do so by conducting desorption and bioavailability experiments with field‐contaminated sediments collected from New York Harbor, New York, USA. Three classes of organic contaminants, polychlorinated biphenyls (PCBs), polycyclic aromatic hydrocarbons (PAHs), and linear alkylbenzenes (LABs) were studied. In order to address the effects of contaminant aging, we compared the contaminant desorption rates from sediments collected from surface and at depth in an area of known high‐sediment accumulation to retarded intraparticle model predictions. Measured desorption rates of the LABs and the most hydrophobic PCBs compare well with model predictions. However, the PAH and less hydrophobic PCB desorption rates range from one to four orders of magnitude slower than model predictions. We postulate that these compounds are present in a resistant sedimentary phase and may represent only a small fraction of what was originally sorbed. The fraction of PCBs, PAHs, and LABs desorbed after 48 h correlate well with measured biota‐sediment factors (BSFs) in Yoldia limatula that were exposed to the same sediments, indicating that desorption rate‐limited assimilation. Several studies have related field BSFs with log Kow and have observed a maximum at intermediate Kows (∼6.0‐6.5). This maximum may be due to predictably slow desorption of high‐Kow compounds and may be lower than predicted rates and extent of desorption of the low‐Kow compounds because of association with resistant phases.

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