This project directly addresses NIEHS Superfund Mandate #4 for the development of “basic biological, chemical, and physical methods to reduce the amount and toxicity of hazardous substances” [22]. Project 5 will help USEPA understand whether activated carbon (AC) is an effective soil/sediment amendment to sequester PCDD/Fs in forms that eliminate their mammalian bioavailability and toxicity, and thus protect human and ecosystem health. Project 5 will test a cause-and-effect relationship for the rates at which AC can reduce or eliminate mammalian bioavailability by measuring a multi-year time series for a) the rates at which AC amendments accumulate PCDD/Fs and b) the mammalian bioavailabilities of PCDD/Fs from these same soils.