Water pH is predicted to affect the uptake of ionisable pharmaceuticals in fish. The current study used an in vitro primary fish gill cell culture system (FIGCS) to assess the effect of pH-values in the range of 4.5 – 8.75 on the uptake rates of the base propranolol (pKa 9.42) and the acid ibuprofen (pKa 4.59). The rate limiting step in uptake was the diffusive supply flux of the unionised form from the water to the apical membrane, with subsequent rapid transfer across the epithelium. Computed uptake rate based on the unionised fraction best described the uptake of propranolol and ibuprofen over the range of pH values 5 – 8 and 6 – 8.75 values, respectively. For ibuprofen the computed uptake rate overestimated uptake below pH 6 where the unionised fraction increased from 4% at pH 6 to 55% at pH 4.5. As the unionised fraction increased the uptake rate plateaued suggesting a saturation of the transport process. For both drugs large variations in uptake occur with only small fluctuations in pH values. This occurs between pH 6 to 8 values, the pH range acceptable in regulatory test guidelines and seen in most of our freshwaters.
- Environmental pharmaceuticals
- Environmental Contamination
- Rainbow trout