Concentrations, accumulations, and inventories of polychlorinated dibenzo-p-dioxins and dibenzofurans in sediments of the Great Lakes

The chronology of PCDD/F accumulation was determined in sediment cores from Lakes Superior, Michigan, and Ontario and two small ''control'' lakes. Accumulation rates began increasing about 1940, increased to maxima at 1970 +/- 10 yr, and then declined to the present rates that are 30-70% of the maxima. The observed accumulations ranged from <0.03 ng cm(-2) yr(-1) in the control lakes and Lake Superior to 0.39 ng cm(-2) yr(-1) in Lake Ontario. By comparing the PCDD/F sedimentary accumulation in the control lakes to those in the Great Lakes, we estimate that Lake Superior receives similar to 0%, southern Lake Michigan receives similar to 20%, northern Lake Michigan receives similar to 60%, and Lake Ontario receives >90% of their current PCDD/F inputs from subregional atmospheric (air parcels having higher concentrations of PCDD/F than remote air due to local sources) and/or non-atmospheric sources. We also compared the sedimentary accumulations to estimates of atmospheric deposition. The PCDD/F accumulation rates in the control lakes were similar to atmospheric deposition of PCDD/Fs from remote air in the Great Lakes basin. Atmospheric deposition from suburban air can support the accumulation of PCDD/F in southern Lake Michigan but some non-atmospheric sources to northern Lake Michigan are implicated. Lake Ontario may be receiving >70% of its current inputs of PCDD/F from non-atmospheric sources.