Persistence of gemfibrozil, naproxen and mefenamic acid in natural waters

The occurrence of pharmaceuticals in natural waters is a potential threat to human nutrition and ecosystem quality. The persistence of the acidic pharmaceuticals gemfibrozil, naproxen and mefenamic acid was studied in surface waters of Maracaibo Lake and Tule reservoir (Venezuela) under laboratory conditions. A quick and easy analytical method was developed for the determination of the acidic drugs at microgram per liter levels using aqueous derivatization, liquid-liquid extraction and gas chromatography-mass spectrometry. Pharmaceuticals degradation followed a pseudo first-order kinetic and their half-lives were calculated for every experimental condition. Under sunlight, naproxen and mefenamic acid were degraded at moderate rates with half-lives from 9.6 +/- A 0.5 to 27.0 +/- A 6.6 days, while gemfibrozil had a higher persistence (t (1/2) = 119.5 +/- A 15.6 - 288.8 +/- A 61.3 days).