SREL Reprint #2288

Estimating the oral bioavailability of methylmercury to channel catfish (Ictalurus punctatus)

John T. McCloskey1, Irvin R. Schultz2, and Michael C. Newman3

1University of Georgia, Savannah River Ecology Laboratory, PO. Drawer E, Aiken, South Carolina 29802, USA
2Battelle PNNL, Molecular Biosciences, PO. Box 999-P7-56, Richland, Washington 99352, USA
3College of William and Mary, Virginia Institute of Marine Science, P.O. Box 1346, Gloucester Point, Virginia 23062, USA

Abstract: In classical pharmacology, oral bioavailability of a toxicant is defined as that fraction of an orally administered dose reaching the systemic circulation of the animal. The present study estimates the bioavailability of methylmercury in channel catfish (Ictalurus punctatus) by comparing concentrations in the blood through time after oral and intra-arterial (IA) administration. Catfish were cannulated in the dorsal aorta and gavaged a pelleted feed that had been spiked with methylmercury. Each catfish was gavaged an increasing amount of spiked feed. Following oral dosing, serial blood samples were removed for more than 1,500 h. One month after removal of the last blood sample, the same fish were injected IA with methylmercury and serial blood samples were removed for more than 3,000 h. The area under the curve of the blood concentration-time curve extrapolated to infinity (AUCo→x) was calculated from fish dosed orally and IA using both noncompartmental (trapezoidal) and compartmental methods. Bioavailability was estimated as the ratio of the dose-corrected oral AUCo→x to the IA AUCo→x.  Average bioavailability estimates from this approach were 33% using noncompartmental (range 14-55%) and 29% using compartmental (range 12-42%) methods and were correlated with the amount of food gavaged to the fish (r2=0.95, p=0.026). Bioavailability estimates using the present methods were much lower than estimates using more conventional methods (i.e., assimilation efficiency estimates using mass balance), suggesting that conventional methods may overestimate the true bioavailzibility of toxicants in fish.

Keywords: Oral bioavailability, Methylmercury, Channel catfish, Elimination, Uptake

SREL Reprint #2288

McCloskey, J.T., I.R. Schultz, and M.C. Newman. 1998. Estimating the oral bioavailability of methylmercury to channel catfish (Ictalurus punctatus). Environmental Toxicology and Chemistry 17:1524-1529.

This information was provided by the University of Georgia's Savannah River Ecology Laboratory (srel.uga.edu).