Atmospheric Inputs of Polychlorinated Dibenzo-p-dioxins and Dibenzofurans to the Great Lakes: Compositional Comparison of PCDD and PCDF in Sediments

Concentrations and accumulations of polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) were determined in dated sediment cores from three of the Great Lakes and two remotely located “control lakes” to assess how inputs of the compounds vary currently and historically among the lakes. The current PCDD accumulation rates in the Great Lakes ranged from a low of 0.0075 ng/cm 2/yr in Lake Superior to a high of 0.22 ng/cm 2/yr in Lake Ontario. PCDF accumulation rates ranged from a low of 0.00078 ng/cm 2/yr in Lake Superior to a high of 0.23 ng/cm 2/yr in Lake Ontario. The relative importance of atmospheric versus non-atmospheric sources of PCDDs and PCDFs to the lakes was estimated by comparing homolog compositions and accumulation rates among cores and homolog-specific accumulation rates to estimates of atmospheric deposition. The estimates are that the atmosphere currently provides (a) 100% of PCDD and PCDF to Lake Superior, (b) 100% of PCDD to southern Lake Michigan, 33–50% of PCDD to northern Lake Michigan, but only 5–35% of PCDF to Lake Michigan, and (c) only 5–35% of PCDD and < 5% of PCDF to Lake Ontario. By comparing the sediment homolog compositions to those of non-atmospheric sources, likely non-atmospheric sources are suggested.