[H-3] 2,3,7,8-TCDD UPTAKE AND ELIMINATION KINETICS OF MEDAKA (ORYZIAS-LATIPES)

Uptake and elimination rate constants for [H-3]-2,3,7,8-tetrachlorodib enzo-p-dioxin ([H-3]TCDD) were estimated by exposing medaka (Oryzias l atipes) to [H-3]TCDD in flowing water with no solvent carriers. Uptake was determined from body burdens measured on exposure days 0, 2, 4, 6 , 10, and 12. Elimination was quantified from whole fish after 28, 90, and 175 d in uncontaminated water. Medaka accumulated [H-3]TCDD at a rapid rate, achieving residues 24,000 times the water concentration af ter 12d, with no indication of approach to steady state. After 6 month s in uncontaminated water, the pg TCDD/g decreased by 69%, much of the decrease due to growth dilution as evidenced by only a 47% decrease i n the pg TCDD/fish. Uptake and elimination rate constants (2,300 ml/g/ d and 0.0045/d, respectively) were estimated by fitting a one-compartm ent, linear, mass-balance model to the data, adjusting for growth rate . The experimental design, including solvent-free delivery of [H-3]TCD D, exposure at concentrations below maximum water solubility, and meas urement of fish growth and lipid content during a 6-month elimination phase, resulted in a predicted steady-state bioconcentration factor (B CF) for medaka of 510,000, a number considerably higher than previousl y reported for dioxin BCFs. Kinetic parameters were used to successful ly predict TCDD BCF in medaka exposed independently.