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

Desorption kinetics of sulfonamide and trimethoprim antibiotics in soils assessed with diffusive gradients in thin-films

Although sorption/desorption of antibiotics in soils affects their mobility and availability, with consequences for risks to the surrounding environment, the dynamics of these processes are not well-known. In this study, diffusive gradients in thin-films devices suitable for measuring polar organic compounds (o-DGT) were deployed in two soils for a range of times (5 h to 20 d) to measure the distribution and rates of exchange between solid phase and solution of three sulphonamides (SAs; sulfamethoxazole, SMX; sulfamethazine, SMZ; and sulfadimethoxine, SDM) and trimethoprim (TMP). o-DGT continuously removes antibiotics to a XAD gel layer after passage through a well-defined diffusion layer and therefore perturbs their concentration in the adjacent soil solution. This induces a remobilization flux from the solid phase, which is related to the concentration of antibiotics in the soil solution, their diffusional supply, and the exchange kinetics between dissolved and sorbed antibiotics. A dynamic model of solute interactions called DIFS (DGT induced fluxes in soils) was used to derive distribution coefficients for labile antibiotics (Kdl) and the rate constant for supply of antibiotics from solid phase to solution, expressed as a response time (Tc). Larger labile solid phase pools were observed for TMP than for SAs. The soils could resupply TMP so rapidly that in one soil, where Tc = 2 min, supply was controlled by diffusion. Response times for SAs were generally longer (>27 min), particularly for SDM (>3 h), implying that the supply of SAs to o-DGT samplers was limited by the desorption release rate. A wider implication of this study is that similar solid phase release kinetics may control the uptake of antibiotics by biota