The potency of a chemical to undergo accumulation within an organism is one of the most important properties evaluated during risk assessment of chemicals. Bioaccumulation occurs when uptake processes outcompete those of elimination and biotransformation. While bioaccumulation is conventionally assessed in resource-intensive animal experiments using fish, we work towards the application of permanent cell lines to predict bioaccumulation. We do this by measuring chemical uptake and biotransformation rates not only in cells of a rainbow trout liver cell line (RTL-W1), but also an intestinal (RTgutGC) as well as a gill (RTgill-W1) cell line to account for possible sites of biotransformation other than the liver. We are working to assess the applicability of our techniques to a wide range of chemicals, with technically challenging physico-chemical properties, such as ionizability, high volatility and hydrophobicity; and to advance Physiologically Based Toxicokinetic (PBTK) models to accurately extrapolate bioaccumulation at the cellular level (in vitro) to the whole organism (in vivo).