Solar transformation and photocatalytic treatment of cocaine in water: Kinetics, characterization of major intermediate products and toxicity evaluation

The present manuscript describes for the first time the transformation and mineralization of cocaine (COC) in water (distilled water (DW) and synthetic municipal wastewater effluent (SWeff)) by natural solar irradiation and two solar photocatalytic processes: heterogeneous photocatalysis with titanium dioxide (TiO2) and homogeneous photocatalysis by photo-Fenton. The solar photocatalytic processes were run at equivalent pilot-plant scale by means of compound parabolic collectors, which allowed for comparison of solar transformation kinetics and compound mineralization. Direct photolysis resulted in almost complete and partial disappearance of COC in SWeff and DW, respectively, after 33 h of normalized irradiation time, and negligible mineralization. Solar transformation of COC by heterogeneous photocatalysis with TiO2 was completed after 28 and 50 min of illumination in DW and SWeff, respectively, whereas about half of the irradiation time was needed with photo-Fenton, which was also proved to be more effective in compound mineralization. Kinetics parameters were calculated for process comparison. Additionally, the phototransformation intermediates generated during each treatment were investigated and characterized by means of ultra-performance liquid chromatography coupled to quadrupole-time of flight tandem mass spectrometry (UPLC-QqTOF-MS/MS). Identity confirmation was possible for some of them with the analysis of commercially available analytical standards. The main COC phototransformation pathways were observed to be ester bond cleavage, hydroxylation, and demethylation. Finally, the application of an acute toxicity test (Vibrio fischeri) to selected water samples resulted in inhibition percentages of bacterial bioluminescence in most cases below 20% after 30 min of sample contact, which indicates low acute toxicity of the photointermediates generated during the different treatments.

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► Study of the photolytic and photocatalytic transformation of cocaine in water.
► Transformation efficiency: photo-Fenton > TiO2 photocatalysis > solar irradiation
► Most phototransformation products coincide with known cocaine metabolites.
► Main phototransformation routes: ester bond cleavage, hydroxylation, and demethylation.
► Photointermediates were slightly more toxic than cocaine. Overall, low toxic effects.