Dissolved organic macromolecules reduce the uptake of hydrophobic organic contaminants by the gills of rainbow trout (Salmo gairdneri)

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Abstract
The effect of the binding of two model hydrophobic organic contaminants, benzo[a]pyrene and 2,2′,5,5′ ‐tetrachlorobiphenyl, to Aldrich humic acid, a commercially available source of dissolved organic macromolecules (DOM), on the uptake of these contaminants by the gills of rainbow trout (Salmo gairdneri) was examined. The efficiency with which trout gills extracted the contaminants from water (with and without DOM present) was measured using a fish metabolic chamber that separated exposure water from water that passed over the gills. Measurements of the contaminant extraction efficiency of trout gills were compared with measurements of contaminant binding to DOM. Contaminants bound to DOM did not diffuse across the gill membrane. Percentage reductions in the concentration of freely dissolved contaminant were equal to percentage reductions in the uptake of the contaminant by the gills. Thus, only the freely dissolved contaminant appears to be available for uptake by fish gills. These correlations between the concentration of freely dissolved contaminant and the fraction of the exposure concentration that is transferred across the gills provide a basis for predicting contaminant dose based on physicochemical measurements of contaminant binding to naturally occurring DOM in the aquatic environment.

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