## 1 Introduction  
The role of glucocorticoids in biochemistry is difficult to exaggerate. The many possible configurations and the various chemical functions present explain the variety of reactions they catalyze in the cell and the sophisticated machinery that, starting from the regulation of glucocorticoid secretion by the hypothalamic-pituitary-adrenal (HPA), governs virtually all of the physiological processes, such as metabolism, immune and cardiovascular functions, skeletal growth, reproduction, and cognition [1, 2]. Specifically, glucocorticoids (GCs) can inhibit immunological, inflammatory, and allergic processes in our body in response to an outer stimulus. Since their coming in the 1950s, many synthetic molecules have been synthesized to increase pharmacological activity and reduce side effects [3]. Due to their therapeutic properties and low cost, GCs are currently the most frequently used class of drugs to treat rheumatic and inflammatory diseases. As recently reported, the yearly number of prescribed GCs largely exceeds that of estrogens and androgens [4], although their use as doping agents and prophylactic in husbandry was banned by the World Anti-Doping Agency and by the Council Directive 96/22/EC, respectively [5, 6]. Their occurrence in freshwaters, mainly as the initial drugs or slightly metabolized compounds, suggests that urban wastewater treatment plants (WWTPs) cannot remove them quantitatively [7]. Indeed, just as many other drugs, they have been detected worldwide in the aquatic environment. River concentrations are in the ng L\({}^{-1}\) or sub-ng L\({}^{-1}\) range in European [4; 8; 9; 10; 11] and non-European countries [12; 13; 14; 15; 16]. On the other hand, significantly higher levels, ranging from few tens to some hundred nanograms per liter, have been measured in WWTPs and hospital wastewaters [17]. In particular, influent WWTPs contain massive GCs amounts, up to 2 ug L\({}^{-1}\). Besides, some tens of ng per gram have been found in sewage sludge samples [9; 18]. These concentrations are high enough to cause a negative eco-toxicological impact on various aquatic organisms, as demonstrated by the plethora of papers devoted to this issue. Under these conditions, reproduction, growth, and development of aquatic biota are affected by chronic exposure to low levels of GCs [19; 20; 21; 22]. It was also reported that GCs act additively [22] and have cumulative effects in mixture with other steroid classes [20]. Depollution is a critical issue because of their negligible volatility and low biodegradability in urban WWTPs [7]. Due to the above, new strategies to abate GCs and those emerging contaminants of the aquatic environment that affect endogenous steroid actions have to be taken into account. In a recent paper [23], we studied the possibility of addressing this issue through direct photolysis in natural water. However, GCs photoreactivity under environmental conditions was found to be almost negligible due to their rigid cyclopentarbropenathrene structure and their limited light absorption in such highly diluted solutions, also when a more absorbing moiety, such as cross-conjugated chromophore in ring A, was present in the structure (see Scheme 1, X = H, F, Y = OH, O). We then decided to explore the possibility of improving the light-driven depollution process by adding a photocatalyst into the equation. Photocatalytic degradation of organic pollutants, such as drugs, has already demonstrated to be a highly effective process, also compared with other advanced oxidation processes (AOPs), and titania semiconductors are the benchmark in terms of efficiency and efficacy compared with other semiconductor oxides, under both UV-A and solar light ([24; 25; 26] and references therein). To date, the effectiveness of TiO\({}_{2}\) photocatalysis for removing GCs under actual conditions, viz. low-level concentrations and natural waters, has not yet been investigated.