A Time-Trends Study of the Occurrences and Levels of CDDs, CDFs and Dioxin-Like PCBs in Sediment Cores from 11 Geographically Distributed Lakes in the U.S.
Polychlorinated dibenzo-p-dioxins (CDDs), polychlorinated dibenzofurans (CDFs) and certain non- and mono-ortho substituted polychlorinated biphenyls (cp-PCBs) are a general class of chlorinated aromatic compounds that are considered as dioxin-like. Because these chemicals are highly toxic, are resistant to physical, chemical and biological degradation and transformation processes, are highly lipophilic and bioaccumulate into ecological and agricultural food chains, attention has been directed to the identification of anthropogenic source activities with the objective of reducing the overall environmental burden. In this regard, certain fundamental questions arise as to environmental trends over time in terms of environmental concentrations and fluxes to environmental sinks. When did these chemicals initially appear in the general environment and are they related to anthropogenic activities? What has been the chronology of environmental burden from the recent time to decades in the past in terms of environmental concentrations and fluxes to the sink? Is there evidence of any trends in environmental burden with time? To address these fundamental questions, the United States Environmental Protection Agency (USEPA) in collaboration with the United States Department of Energy (USDOE) has completed a time-trends study of the occurrences and levels of CDDs, CDFs and cp-PCBs in the U.S. environment using dateable sediment deposits obtained from 11 freshwater lakes geographically distributed in the United States. The objective of the USEPA/USDOE study was to determine the chronology of the deposition of dioxin-like compounds in the United States over the past 200 hundred years.