Historical input and degradation of toxaphene in Lake Ontario sediment

The historical input of toxaphene to Lake Ontario has been determined. We analyzed total toxaphene concentrations in eight Lake Ontario sediment cores by electron capture gas chromatographic mass spectrometry and found that toxaphene maximizes in 1973 +/- 6 yr with a horizon date of 1945 +/- 6 yr. The maximum toxaphene flux to Lake Ontario sediment was 22 +/- 8 mu g/m(2) yr in about 1973, and the total toxaphene load in the lake is 10 +/- 3 t. By comparing the toxaphene burdens for the cores, we conclude that toxaphene is deposited to Lake Ontario sediment from both the Niagara River and from the atmosphere. We also found that toxaphene is slowly dechlorinated after deposition in Lake Ontario sediment.