Polybrominated diphenyl ether (PBDE) flame retardants have become distributed ubiquitously in the environment. High concentrations have been reported in U.S. sewage sludge (biosolids). The burgeoning practice of land-applying biosolids as fertilizer creates an avenue for reintroduction of PBDEs to surface waters and aquatic sediments. Bioavailability of biosolids- and sediment-associated PBDEs was assessed using the freshwater oligochaete, Lumbriculus variegatus. Oligochaetes were exposed to composted biosolids (1,600 ng/g total PBDEs) and artificial sediment spiked with penta- and deca-brominated diphenyl ether (BDE) formulations (1,300 ng/g total PBDEs). Uptake (28-d exposure) and depuration (21 d) of eight congeners were studied. Polybrominated diphenyl ethers in both substrates were bioavailable, but bioaccumulation was 5 to 10 times greater from spiked artificial sediment. The congeners BDE 47 and BDE 99 were the most prevalent congeners in oligochaetes after exposure. Congener BDE 47 was more bioaccumulative, possibly due to the threefold greater depuration rate of BDE 99. Bioaccumulation of penta- and hexa-brominated congeners appeared to be affected more strongly by substitution pattern than degree of bromination. Uptake of BDE 209, the dominant congener in deca-BDE, was minimal. Accumulation of certain PBDE congeners from biosolids and sediments by benthos provides a pathway for transfer to higher trophic levels, and congener discrimination may increase with each trophic transfer.