Determination of the bioavailability of selected pharmaceutical residues in fish plasma using liquid chromatography coupled to tandem mass spectrometry

- A bioanalytical method was developed to analyze pharmaceuticals in fish plasma.
- Solid phase extraction of 100 μL of fish plasma was performed.
- LC-MS/MS analysis was conducted within 14 min.
- Low to undetected levels of selected pharmaceutical residues were found in northern pike plasma.
- Bioavailability of drugs in environmentally exposed fish depended on their physico-chemical properties.

Aquatic systems near major urban centers are constantly contaminated with effluent from wastewater treatment plants. Pharmaceuticals are part of the contamination and several classes of drugs have been detected in surface waters in the last decade. To better understand the impact of those pharmaceuticals in ecosystems, the exposure to aquatic species needs to be investigated. This study presents a new simple and rugged quantitative method for the determination of several classes of drugs using 100 μL of plasma from fish environmentally exposed to a major but highly diluted urban effluent. Six common drugs (i.e., diclofenac, ibuprofen, naproxen, salbutamol, sulfamethoxazole and trimethoprim) and one major metabolite (2-hydroxy-ibuprofen), present in significant amount in impacted waterways have been selected for the development and validation of the method. First, all drugs were extracted using cation exchange solid phase extraction (SPE) and eluted with two solvent mixtures. Then, the extracts were analyzed using a reverse-phase analytical column Waters® CORTECS C18+ (150 × 2.1 mm, 2.7 μm) within 14 min. MS/MS was performed with an electrospray (ESI) interface in positive ion mode, with multiple reaction monitoring (MRM) experiment acquiring two product ions per drugs. Quantification has been made with standard curves for each analyte using isotopically labeled internal standards. This method has high sensitivity with limits of quantification of 1 ng mL−1 for each drug, except for ibuprofen and its metabolite 2-hydroxy-ibuprofen at 2 ng mL−1. The precision of the method was below 11%, the accuracy between 94 and 105% and overall recovery between 94 and 111% for all drugs, with high selectivity. Application of the method to plasma samples from wild northern pike inhabiting the St. Lawrence River collected over a three-year period showed the presence of naproxen, diclofenac, trimethoprim and salbutamol at very low concentrations (around 1 ng mL−1).