Accumulation of 2,3,7,8-tetrachlorodibenzo-p-dioxin by rainbow trout (Onchorhynchus mykiss) at environmentally relevant dietary concentrations

Rainbow trout were fed a diet containing 1.8, 18, or 90 pg/g H-3-2,3,7,8-te trachlorodibenzo-p-dioxin (TCDD) for up to 320 d. Concentrations of TCDD we re determined in muscle, liver, and ovaries at 100, 150, 200, and 250 d. Co ncentrations of TCDD reached an apparent steady-state concentration in live r after 100 d of exposure, whereas concentrations in other tissues continue d to increase until 150 d of exposure. The greatest portion of the total ma ss of TCDD was present in the muscle tissue with lesser proportions in othe r organs. As the ovaries developed before spawning, an increase occurred in the total mass of TCDD present in this tissue. The assimilation rate of TC DD during the initial 100 d of the exposure was determined to be between 10 and 30%. This is somewhat less than estimates derived based on both uptake and elimination constants determined during shorter exposures. Biomagnific ation factors (BMFs) were estimated for all tissues and exposure concentrat ions, and at all exposure periods. Lipid-normalized BMFs for muscle ranged from 0.38 to 1.51, which is consistent with the value of 1.0 predicted from fugacity theory. Uptake and depuration rate constants were determined and used to predict individual organ TCDD concentrations. Comparison with obser ved values indicated that the model could be used to predict tissue concent rations from the known concentrations of TCDD in food. This model will allo w more refined risk assessments by predicting TCDD concentrations in sensit ive tissues such as developing eggs.