Fate of citalopram during water treatment with O3, ClO2, UV and fenton oxidation

► Citalopram was degraded by O 3 , ClO 2 , UV-irradiation and fenton oxidation . ► Five transformation products of citalopram were identified. ► Three transformation products are new to the science. In the present study we investigate the fate of citalopram (CIT) at neutral pH using advanced water treatment technologies that include O 3 , ClO 2 oxidation , UV irradiation and Fenton oxidation. The ozonation resulted in 80% reduction after 30 min treatment. Oxidation with ClO 2 removed >90% CIT at a dosage of 0.1 mg L −1 . During UV irradiation 85% reduction was achieved after 5 min, while Fenton with addition of 14 mg L −1 (Fe 2+ ) resulted in 90% reduction of CIT. During these treatment experiments transformation products (TPs) were formed from CIT, where five compounds were identified by using high resolution and tandem mass spectrometry. Among these desmethyl-citalopram and citalopram N-oxide have been previously identified as human metabolites, while three are novel and published here for the first time. The three TPs are a hydroxylated dimethylamino-side chain derivative, a butyrolactone derivative and a defluorinated derivative of CIT.