Direct and indirect photodegradation pathways of cytostatic drugs under UV germicidal irradiation: Process kinetics and influences of water matrix species and oxidant dosing

Abstract

The ever-increasing consumption of various cytostatic drugs (CSDs) has attracted growing public concern in recent years. The photodegradation of 8 CSDs was investigated using a low-pressure UV-254Hg lamp, resulting in fluence-based first-order kinetic rate constants in the range of (0.20-6.97)×10^-4cm²mJ^-1. The influence of water matrix components, including natural dissolved organic matter (DOM), bicarbonate (HCO₃^-), nitrate (NO₃^-), chloride (Cl^-), and sulfate (SO₄^2-), was investigated. The degradation rates of CSDs decrease in the presence of DOM due to the competition for the UV light, but increase with addition of NO₃^- due to an indirect production of HO. Further investigation was carried out to evaluate the viability of UV treatment performances using two real water samples, namely treated water from a water treatment plant and secondary effluent from a wastewater treatment plant. The primary photodegradation byproducts of CSDs were identified using LC/MS/MS to investigate the mechanism of direct UV photolysis and indirect NO₃^--induced and DOM-induced photolysis. The degradation rates of CSDs increase significantly with the addition of H₂O₂ or S₂O₈^2- under UV irradiation, due to the generation of non-selective HO or selective SO₄^-. As an electrophilic radical, SO₄^- mainly reacts via electron transfer and selectively attacks certain electron-donating functional groups of CSDs.

Keywords: Cytostatic drugs; Degradation pathway; UV photolysis; Water matrix.