Recently performed environmental risk assessments of ivermectin demonstrated the need to complete the information regarding the fate of ivermectin in environment. There is also a lack of information concerning the fate and stability of praziquantel. The forced degradation study and photocatalytic degradation pathways in aqueous TiO2 suspensions of the two anthelmintics ivermectin and praziquantel were investigated and compared. The degradation efficiency increased for both compounds with the increase in the TiO2 concentration from 0.25 to 2.00 g L(-1), and then remained constant. The estimated k-values were from 0.36 h(-1) to 0.64 h(-1) for IVE and from 0.29 h(-1) to 0.47 h(-1) for PZQ, respectively. The degradation rate was not significantly impacted by the change of the pH value (pH 3, 5, 7, and 9) at 2.0 g L(-1) of TiO2. The photo degradation was about 90% for both compounds after 5 h of irradiation and it was significantly inhibited in the presence of iodide anion and isopropyl alcohol, which indicated, that hydroxyl radicals as well as holes contributed to the degradation of both anthelmintics. The contribution of hydroxyl radicals and holes was 92.1% for IVE and 93.2% for PZQ, respectively. Photocatalytic process of ivermectin resulted in three degradation intermediates; another two were formed during acidic and basic hydrolysis. Praziquantel underwent degradation to six degradation intermediates; four of them were formed under photocatalytic irradiation. The intermediates were identified using UHPLC-MS/MS. UV/TiO2 photolysis has been found as an effective advanced oxidation technology for the decontamination of ivermectin and praziquantel.

Charles University Prague Faculty of Pharmacy Department of Analytical Chemistry Heyrovského 1203 500 12 Hradec Králové Czech Republic

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