Degradation of indomethacin in river water under stress and non-stress laboratory conditions:degradation products,long-term evolution and adsorption to sediment

摘要

The pharmaceutical compound indomethacin is not totally removed in wastewater treatment plants,whose effluents flow into aquatic environments;concentrations in the 0.1-100 ng/L range are commonly found in surface waters,and its fate is unknown.Here,biological,photochemical and thermal degradation assays were conducted under stress and non-stress conditions to estimate its degradation rate in river water and establish its degradation products over time.The results revealed that direct sunlight irradiation promoted the complete degradation of indomethacin(2 μg/L) in less than 6 hr,but indomethacin was detected over a period of 4 months when water was kept under the natural day-night cycle and the exposure to sunlight was partially limited,as occurs inside a body of water.The biological degradation in water was negligible,while the hydrolysis at pH 7.8 was slow.Residues were monitored by ultra-pressure liquid chromatography/quadrupole time-of-flight/mass spectrometry after solid-phase extraction,and six degradation products were found;their structures were proposed based on the molecular formulae and fragmentation observed in high-resolution tandem mass spectra.4-Chlorobenzoic and 2-acetamido-5-methoxybenzoic acids were the long-term transformation products,persisting for at least 30 weeks in water kept under non-stress conditions.Furthermore,the degradation in the presence of sediment was also monitored over time,with some differences being noted.The adsorption coefficients of indomethacin and degradation products on river sediment were calculated;long-term degradation products did not have significant adsorption to sediment.