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Uptake and elimination of ionizable organic chemicals at fish gills: I. Model formulation, parameterization, and behavior
Author(s) -
Erickson Russell J.,
McKim James M.,
Lien Gregory J.,
Hoffman Alex D.,
Batterman Sharon L.
Publication year - 2006
Publication title -
environmental toxicology and chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.1
H-Index - 171
eISSN - 1552-8618
pISSN - 0730-7268
DOI - 10.1897/05-358r.1
Subject(s) - chemistry , membrane , alkalinity , gill , diffusion , molecule , environmental chemistry , facilitated diffusion , chemical species , biophysics , flux (metallurgy) , inorganic chemistry , fish <actinopterygii> , organic chemistry , biochemistry , thermodynamics , physics , fishery , biology
A mechanistic model for the uptake and elimination of ionizable organic chemicals at fish gills is presented. This model is a modification of a previous model for nonionizable organic chemicals that addressed the transport of chemical to and from gill surfaces in water and blood, diffusion of chemical across epithelial cells, and binding of chemical to components in water and blood. For ionizable chemicals, three additional processes are included. First, excretory products alter the pH at gill surfaces, affecting the relative amounts of neutral and ionized molecules compared with that in the bulk exposure water. Second, ionized molecules support chemical flux to and from epithelial cell membranes and help maintain high diffusion gradients of neutral molecules across these membranes, thereby contributing to uptake and elimination even if the membranes are impermeable to ionized molecules. Third, membrane barriers are not completely impermeable to ionized molecules, and even limited permeability can have appreciable effects on chemical flux. Approaches for model parameterization are discussed. Model‐predicted relationships of uptake and elimination rates to exposure water pH, alkalinity, and chemical properties are presented and discussed in terms of model processes. The model is shown to predict important features of reported effects of pH on uptake rates of weak organic acids.