Perfluorooctane sulfonamidoethanol based phosphate diester (SAmPAP) is a potential perfluorooctane-sulfonate (PFOS) precursor. To examine whether SAmPAP exposure would result in fish contamination by perfluoro and polyfluoroalkyl substances (PFASs), juvenile Eurasian perch were dietarily exposed to this compound (dosed group) or exposed to the same tank water but fed control feed (control group). SAmPAP and metabolites were monitored in the muscle, liver, and serum during the 45-day exposure phase and 35-day depuration phase. SAMPAP' was only detected in the dosed group and the absorption efficiency (0.04-2.25%) was very low, possibly related to its low-bioavailability in the gastrointestinal tract, steric constraints in crossing biological membranes, and clearing by enterohepatic circulation. Although SAmPAP was biotransformed and eliminated at a slow rate (t(1/2). > 18 days), its biomagnification factor was low. The observed metabolites in fish were N-ethyl perfluorooctane sulfonamidoacetic acid, perfluorooctane sulfonamidoacetic acid, perfluorooctane sulfonamide, and PFOS. Considering that SAmPAP was the only source of PFASS in the tanks, the occurrence of Metabolites indicates that SAmPAP could be biotransfOrmed in fish and contribute to PFOS bioaccumulation. However, levels of metabolites were not significantly different in the dosed and control groups, indicating that metabolite excretion followed by re -exposure to these metabolites from water was the main uptake route. (GRAPHICS)