Brominated diphenyl ethers (BDEs) are organic chemicals used as flame retardants that have become ubiquitous in the environment. Sediment exposure assessments have not been conducted for BDEs and are necessary for understanding their potential impacts in coastal environments. Field studies and laboratory experiments were conducted to determine the bioavailability of BDEs from sediments to deposit-feeding invertebrates in order to investigate potential transfer to higher trophic levels in estuarine environments. In field studies, accumulation of congeners in the Penta-BDE mixture was similar to PCBs with similar Kow. BDE 209, the dominant congener in sediments, was not detected in invertebrates despite sediment concentrations up to 4000 ng/g dry weight. In 28 and 56 day exposures to Baltimore Harbor sediments, PCBs, PAHs, butyltins and metals were bioavailable to the polychaete worm Nereis virens and the amphipod Leptocheirus plumulosus. However, BDE accumulation was low and BDE 209 was not detected in either species despite sediment concentrations up to 300 ng/g dry weight. To elucidate the mechanism(s) limiting the bioavailability of BDE 209 and determine the relative bioavailability of congeners in the Penta-BDE and Deca-BDE (>97% BDE 209) commercial mixtures, 28 day bioaccumulation experiments were conducted in which N. virens were exposed to spiked sediments, spiked food or field sediments. Selective accumulation of congeners in the Penta-BDE mixture over BDE 209 and other components of the Deca-BDE mixture from spiked sediments support the prevalence of the Penta-BDE congeners reported in higher trophic level species. Bioaccumulation from the spiked substrates demonstrated that BDE 209 is capable of crossing the gut wall. Bioavailability was highly dependent on the exposure conditions however since accumulation of BDE 209 from field sediments did not occur in 28 days (<0.3 ng/g wet weight). When exposed to Deca-BDE in spiked sediments also containing the Penta-BDE commercial mixture and PCB 209, bioaccumulation of BDE 209 was reduced compared to exposure to Deca-BDE alone. The mechanism responsible for limiting accumulation of BDE 209 remains unclear but appears to involve characteristics of the sediment matrix and low transfer efficiency in the digestive fluid and across the gut wall.