In December 1997, the International Joint Commission (hereafter referred to as The Commission or (IJC) released the report of its Nuclear Task Force (also referred to as the Task Force), Inventory of Radionuclides for the Great Lakes (hereafter referred to as the Inventory ). This report presented data on the sources of various radioactive isotopes and used a material balance approach to organize this information to permit various types of assessments with respect to the movement and distribution of radionuclides within the Great Lakes. One component of such a material balance is the radionuclide burden within biota of the various biological communities within the Great Lakes. Estimation of the biological burden of various radioactive elements requires a consideration of the exposure to and uptake, metabolism, excretion, and transfer of these radioactive elements within and among organisms. To address these issues, the Task Force undertook a study of bioaccumulation of radioactive materials from environmental media and substrates and biomagnification of radioactive materials within biota, food chains, and biotic assemblages. The studies undertaken examined a large number of data sets that might be suitable for determination of bioaccumulation and biomagnification parameters for various radioactive forms of elements. At the time of preparation of the Inventory , several of the reviewers indicated that analyses for bioaccumulation and biomagnification should be separately issued by the Commission as reference documents. This report, referred to as the Bioaccumulation Report , is a response to that suggestion.