Toxicokinetics and disposition of inorganic mercury and cadmium in channel catfish after intravascular administration.

To better understand the distribution and elimination of inorganic mercury (Hg) and cadmium (Cd) in fishes, channel catfish (Ictalurus punctatus) were administered either 6.4 micrograms/kg 203Hg as HgCl2 or 4.0 micrograms/kg 109Cd as CdCl2 via a dorsal aortic cannula. Blood, plasma, and red blood cells (RBCs) were serially sampled up to 156 (Hg) or 335 (Cd) days. The fraction of the injected dose remaining in the animal (Xf) was also determined at selected times by whole animal counting. The blood concentration and Xf-time profiles were simultaneously fitted to a three-compartment toxicokinetic model. The plasma concentration-time profile was also separately fitted to the same three-compartment model for comparison of parameter estimates. Toxicokinetic analysis of the blood concentration and Xf-time profile provided the following values: steady-state volume of distribution = 13.8 +/- 2.8 ml/g (Hg), 41.4 +/- 0.3 ml/g (Cd); total body clearance = 0.021 +/- 0.0006 ml/day/g (Hg), 0.0031 +/- 0.0008 ml/day/g (Cd); biological half-life (t1/2, beta) = 722 +/- 309 days (Hg), 9627 +/- 2206 days (Cd). Estimates of the t1/2 beta were up to 94 times longer if determined by simultaneous fitting of the blood concentration and Xf-time profiles. A time-dependent accumulation of Hg and Cd by RBCs was observed with maximum RBC concentrations of Hg and Cd occurring at 7 and 12 days after injection. After injection, the tissues with the highest accumulation of Hg were the liver, trunk and head kidney, muscle, and skin, but the amount of Hg in the liver gradually increased over 156 days. Most of the Cd was accumulated by the liver and trunk kidney within 24 hr, with little change occurring after 335 days. This study demonstrates the usefulness of intravascular injection and simultaneous analysis of blood and whole body amount data in determining the elimination of metals from fishes.