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-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 (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. 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 or selective SO4-. As an electrophilic radical, SO4- mainly reacts via electron transfer and selectively attacks certain electron-donating functional groups of CSDs.

Biological and photochemical degradation of cytostatic drugs under laboratory conditions.

Cytostatic drugs, used in chemotherapy, have emerged as new environmental contaminants due to their recurrent presence in surface waters and genotoxic effects. Yet, their degradability and environmental fate is largely unknown. The aim of this study was to determine the degradation kinetics of 16 cytostatic drugs, prioritized according to their usage and occurrence in hospital and wastewater treatment plants (WWTP) effluents, through the following laboratory scale processes: hydrolysis, aerobic biodegradation, UV-C photolysis, UV-C/H2O2 and simulated solar radiation. Some drugs were unstable in milli-Q water (vincristine, vinblastine, daunorubicin, doxorubicin and irinotecan); others were photodegraded under UV-C light (melphalan and etoposide) but some others were found to be recalcitrant to biodegradation and/or UV-C, making necessary the use of advanced oxidation processes (AOPs) such as UV-C/H2O2 for complete elimination (cytarabine, ifosfamide and cyclophosphamide). Finally, radiation in a solar box was used to simulate the fate of cytostatic drugs in surface waters under natural radiation and complete removal was not observed for any drug. The degradation process was monitored using liquid chromatography coupled to high resolution mass spectrometry and pseudo-first order kinetic degradation constants were calculated. This study provides new data on the degradability of cytostatic compounds in water, thus contributing to the existing knowledge on their fate and risk in the environment.