Our previous research on atmospheric samples suggested that Lake Ontario might receive significant amounts of Dechlorane Plus (DP), a highly chlorinated flame retardant, from the atmosphere and from inputs from DP's manufacturing facility in Niagara Falls, New York. To confirm this suspicion, a sediment core from the central basin of Lake Ontario was analyzed for the two isomers of DP, for polybrominated diphenyl ethers (PBDEs), and for 1,2-bis-(2,4,6-tribromophenoxy)ethane (TBE). The results showed that the concentration of DP in sediment increased rapidly starting in the mid-1970s and reached its peak concentration (310 ng g(-1) dry weight) in the mid-1990s. The peak flux and total inventory of DP were estimated to be 9.3 ng cm(-2) yr(-1) and 120 ng cm(-2), respectively. These values suggest that the total burden of DP in Lake Ontario is approximately 20 tons and that the maximum load rate was approximately 2 tons per year. The highest concentrations of PBDEs and TBE were found in the surficial sediment, with average concentrations of 2.8, 14, and 6.7 ng g(-1) d.w. for PBDE(3-7) (tri-through hepta-BDEs), BDE-209, and TBE, respectively. The surface fluxes were 0.08, 0.43, and 0.20 ng cm(-2) yr(-1), and the inventories were 0.87, 3.9, and 1.8 ng cm(-2) for PBDE3-7, BDE-209, and TBE, respectively. The concentration of DP in Lake Ontario sediment exceeds that of the brominated flame retardants combined.