You are here:
UPTAKE AND ELIMINATION OF IONIZABLE ORGANIC CHEMICALS AT FISH GILLS: PART I. MODEL FORMULATION, PARAMETERIZATION, AND BEHAVIOR
Citation:
Erickson, R J., J M. McKim, G J. Lien, A D. Hoffman, AND S L. Batterman. UPTAKE AND ELIMINATION OF IONIZABLE ORGANIC CHEMICALS AT FISH GILLS: PART I. MODEL FORMULATION, PARAMETERIZATION, AND BEHAVIOR. ENVIRONMENTAL TOXICOLOGY AND CHEMISTRY. SETAC Press, Pensacola, FL, 25(6):1512-1521, (2006).
Impact/Purpose:
To evaluate the effects of pH and alkalinity on uptake and elimination of ionizable organic chemicals in large rainbow trout
Description:
Effects of pH and alkalinity on uptake and elimination of ionizable organic chemicals at the gills of large rainbow trout were studied. Increased pH reduced uptake rates of weakly-acidic chlorinated phenols and increased that of weakly-basic 3,4-dichlorobenzylamine, indicating greater bioavailability of un-ionized molecules than ionized molecules. However, uptake rates were often much greater than expected based on un-ionized chemical concentration in exposure water, indicating some bioavailability of ionized forms. For chlorinated phenols, the pH-dependence of uptake was very similar among chemicals, despite greatly different ionization constants, and increased alkalinity reduced uptake. Elimination rates of chlorinated phenols also exceeded that expected based on un-ionized chemical concentrations in the blood, and varied with exposure water pH. For chlorinated phenols, model calculations indicated that ionized chemical bioavailability could be primarily attributed to diffusion to and from membrane barriers helping to maintain steep gradients of the un-ionized chemical across these membranes. Lower pH at the gill surface also contributed to bioavailability by increasing the concentration of un-ionized molecules. Membrane permeability of ionized forms was not important for explaining bioavailability to chlorinated phenols, but appeared to be important for 3,4-dichlorobenzylamine, and would be more important for chlorinated phenols under other conditions.