## 1 Introduction  
Medical advances have improved human lives, but, at the same time, high industrial production of medicines and the absence of specific methods for their elimination have led to a high level of pollution of both surface waters and, in some cases, soil, plants, and animals [1]. Most of the medicines sold every year worldwide end up in the environment. The causes of this phenomenon are manifold and range from the incorrect disposal of expired products to the industrial discharge of production processes; however, patients may be the biggest cause of this type of pollution. In fact, when a drug is taken, it is absorbed by the body and enters the body's circulation to be distributed and sent to the target site, where it performs its function. Many of the medicines taken, however, are partially expelled without being metabolized [2]. A worrying fact is that the release of drugs into the environment has a higher frequency than the inactivation times of the compounds, which renders them pseudo-persistent. In most cases, the environmental concentrations of pharmaceuticals are too low to directly affect human lives; however, the presence of any drug in superficial waters can affect the local fauna continuously exposed to the drug through contact with the water, leading to the propagation of bioaccumulation problems along the food chain [3]. Pharmaceutical waste, together with sewage, reaches wastewater treatment plants, where the organic loads are degraded and the water is cleaned, but the fate of pharmaceuticals depends on their structural composition and reactivity towards the process used to treat the waste, which can lead to more toxic compounds. Downstream, the waters from wastewater treatment plants are still rich in active ingredients [4; 5; 6; 7], which are poured into channels that carry the pollutants to superficial waters [8; 9; 10; 11; 12; 13]. The fates of drugs in the environment can be very different; in fact, they can simply degrade or persist for a long time (up to 20 years), resulting in accumulation. Irbesartan is considered the progenitor of the Sartan family and is used alone or in combination with other drugs to treat high blood pressure. It can also be used in cases of kidney problems caused by type 2 diabetes mellitus and hypertension and in the treatment of congestive heart failure. Irbesartan, which has been on the market for about 19 years and for which there is an annual production of about 20,000 kilos, is an orally active substance that is absorbed quickly and effectively [14]. After it has exerted its biological effect and been metabolized in the liver, irbesartan is mainly eliminated through the feces, although around 20% is found in the urine. In a recent study conducted on Italian wastewater, satrans were the emerging contaminants found most frequently and at the highest concentrations. In particular, irbesartan was one of the satrans detected in the highest number among the samples analyzed [12]. There have been several studies on the elimination, persistence, and toxicity of satrans [15; 16], but there are no comprehensive data in the literature on irbesartan in relation to its persistence in the environment or its refractoriness to water or wastewater treatment. Irbesartan has been found in samples of surface waters in Africa and Europe at concentrations just below 1 mg/L [17] and, not infrequently, even in drinking water, with concentrations up to 3.0 ng/L [18]. Due to advanced oxidation processes (AOPs), 21% of irbesartan resists normal wastewater purification treatments and is thus released into the environment, while 79% is partially mineralized or transformed into degradation byproducts [19]. In a prior study, the disinfection pathway of irbesartan was examined based on the typical chlorination process employed in wastewater treatment plants (WWTPs) [16; 20]. Six disinfection byproducts (DBPs) were isolated and then completely characterized via a combination of mass spectrometry (MS) and nuclear magnetic resonance (NMR) data.