5-Fluorouracil and Its Prodrug Capecitabine: Occurrence, Fate and Effects in the Environment

In this chapter, we examine the available literature on the cycling and effects of 5-flourouracil (5-FU) and capecitabine (CAP) residues in the aqueous environment. The aim is to understand better their environmental occurrence, fate and potential toxic effects. Physicochemical properties of 5-FU and CAP suggest that they are more likely to remain in aqueous environment than adsorbed to solid particles. Detectable levels have been reported in hospital effluents (< 122 μg/L) and in municipal wastewaters (< 280 ng/L), but rarely in surface waters (only 5-FU in one study: < 160 ng/L). Among different water treatments available, the most promising for removing 5-FU and CAP are the advanced oxidation processes (AOPs). So far, indirect photolysis has been most widely applied and is capable of almost completely removing both compounds (to < LOD) and in some cases resulting in complete mineralization. However, these treatments have been mostly tested in MilliQ or potable water and their suitability for complex matrices like wastewaters is questionable and biodegradation is still treatment of choice for these matrices. In other studies, a variety of transformation products has been identified adding to the overall environmental burden. Toxicity tests on single parent compounds have shown that they may have effects above the concentrations of environmental relevance. The studies of complex mixtures of parent compounds highlight that the actual ecological risk posed by mixtures of these compounds is difficult to evaluate. Overall, the main finding from this review is that a real need exists for further studies on the chemical and toxicological effects of environmental mixtures of cytotoxic compounds.