Concentrations, Accumulations, and Inventories of Toxaphene in Sediments of the Great Lakes

Sediment cores were analyzed for toxaphene from three of the Great Lakes (Superior, Michigan, and Ontario) and from two small control lakes near Lake Superior that receive inputs of toxaphene from only the atmosphere. The two cores from northern Lake Michigan had higher surface concentrations (33 ± 12 ng/g) than the southern Lake Michigan core and the remainder of the Great Lakes cores, which were similar (15 ± 4 ng/g), and similar to the surface concentration in one of the control lakes (9 ng/g). Evidence consistent with the slow degradation of toxaphene ( t 1/2 ≥ 50 yr) in some of the sediment cores was found. The similar concentrations among all the Great Lakes cores and the control lake core provide strong evidence that the dominant source of toxaphene to the Great Lakes is atmospheric input. The higher concentrations in the northern Lake Michigan cores indicate that northern Lake Michigan may be receiving about 30−50% of its current inputs from non-atmospheric sources. Lake Ontario and Lake Superior may have had a non-atmospheric source in the past.