**2.1. Test chemicals, reagents, and standards**

High-purity analytical standards (>97.7%) of the five selected organophosphorus pesticides (azinphos methyl, azinphos ethyl, dimethoate, disulfoton, and fenthion) were purchased from Dr. Ehrenstorfer-Schäfers (Augsburg, Germany) and used without further purification. Their chemical structures and data for selected physicochemical properties of studied OPPs, taken from Ref. [12], are shown in **Table 1**. Titanium dioxide (TiO<sup>2</sup> ) catalyst was Degussa P-25 (Frankfurt, Germany). Hydrogen peroxide (30% solution H<sup>2</sup> O2 ) was obtained from Merck & Co (Darmstadt, Germany). Pesticide-grade and HPLC-grade solvents (acetone, hexane, methanol, and dichloromethane) were supplied from Labscan Ltd. (Dublin, Ireland). Organic-free water used for all aquatic solutions was of specific resistance greater than 18.2 MΩ cm (25°C) and was produced by a Milli-Q/Milli-RO water purification system (Millipore, USA). Individual pesticide stock solutions were prepared by gravimetric weighting of high-purity standards (to concentrations of approximately 1000 mg L−1) in methanol (HPLC-grade) and were stored at -10°C in the dark. Working standard solutions of individual compounds were prepared by appropriate dilutions of the stock solutions. Other chemical reagents used (HCl, NaOH, Na<sup>2</sup> SO4 , and C8 H4 K2 O4 ) were of analytical grade and procured from Merck (Merck, Germany).
