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

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-254 Hg lamp, resulting influence-based first-order kinetic rate constants in the range of (0.20-6.97) x 10(-4) cm(2) mJ(-1). The influence of water matrix components, including natural dissolved organic matter (DOM), bicarbonate (HCO3-), nitrate (NO3-), chloride (Cl-), and sulfate (SO42-), 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 center dot. 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 S2O82- under UV irradiation, due to the generation of non-selective HO center dot or selective Sal. As an electrophilic radical, SO4 center dot- mainly reacts via electron transfer and selectively attacks certain electron-donating functional groups of CSDs. (C) 2016 Elsevier B.V. All rights reserved.