The objectives of this chapter are to review the regulatory tools that apply to bioaccumulation, to summarize the current knowledge on metal bioaccumulation processes, and to propose scientifically defensible approaches for fulfilling the regulatory intent of the use of bioaccumulation data. The chapter is divided into 6 sections. Section 4.2 reviews the rationale behind the regulatory concern over bioaccumulation and the use of various bioaccumulation indices by 3 regional regulatory agencies (United States, Canada, and Europe). Section 4.3 briefly introduces the mechanisms of metal bioaccumulation and the current understanding of the relationship between bioaccumulation and toxicity. Section 4.4 identifies the scientific rationale for considering that certain commonly used bioaccumulation indices do not fulfill the regulatory intent of bioaccumulation, and begins to identify how alternative approaches can be developed. Section 4.5 provides examples of how current scientific knowledge of bioaccumulation may be used to relate it to toxicity and identifies the limitations of these relationships. Section 4.6 discusses how bioaccumulation of different metals can be compared by incorporating bioaccumulation models into the UWM. Bioaccumulation models estimate tissue metal

concentrations, and these concentrations can be compared to threshold dietary toxicity values. Section 4.7 provides the conclusions.