Modeling silver binding to gills of rainbow trout ( Oncorhynchus mykiss )

Rainbow trout ( Oncorhynchus mykiss , 1–3 g) were exposed to ∼0.1 μM silver (Ag) (∼11 μg.L −1 Ag) for 2 to 3 h in synthetic soft water (Ca, Na ∼ 300 μM, pH 6.5–7.5) to which was added Ca, Na, H + , dissolved organic carbon (DOC), CI, or thiosulfate (S 2 O 3 ). Gills were extracted and gill Ag concentrations were measured using graphite‐furnace atomic absorption spectrophotometry. The concentrations of cations (Ca, Na, H + ) and complexing agents (DOC, CI, S 2 O 3 ) needed to keep Ag off the gills were used to calculate conditional equilibrium binding constants ( K ) at the gills. Log K for Ag‐gill binding was 10.0, with approximately 1.3 nmol Ag binding sites per fish. All experimentally determined log K values were entered into an aquatic chemistry equilibrium model, MINEQL + , to predict Ag binding at trout gills. For a series of natural waters, model‐predicted gill Ag concentrations correlated well with observed gill Ag concentrations, with one exception, very hard city of Waterloo tapwater. This exception may indicate a kinetic constraint on the thermodynamic basis of the model.