## 1 Introduction  
Latin America is one of the main sources of fresh water in the world, producing approximately one third. It is estimated that only 20% of municipal wastewater is treated in most of the countries that comprise this region while in Mexico, less than 50% of wastewater is processed [1]. The entry of different types of drugs into the environment has increased by 1 to 5 million tons per year [2, 3], causing concern about adverse environmental impacts related directly to the drugs and their by-products [4]. Due to the high chemical stability of many drugs and the limits of conventional wastewater treatment processes, effluent from treatment plants often contains elevated concentrations of the chemicals and metabolites and thus the wastewater is a source of drug compounds to aquatic ecosystems [2, 5, 6]. Drugs have been detected in different types of water, such as surface water, groundwater, wastewater, and even drinking water [7], where their concentrations vary from ng/L to mg/L [2, 8, 9]. However, even in small quantities, they can cause various consequences, not only in the environment where they are found but also in living beings [2]. As a result of this continuous discharge into the environment, aquatic organisms such as fish, are affected, which may accumulate significant amounts of these chemicals, generating alterations such as feminization or masculinization caused by hormones. As fish and birds are intermediaries in the trophic chain, the ingestion of these organisms when contaminated results in the accumulation of these substances in humans, causing in some cases resistance to antibiotics, endocrine disruption, histopathological disorders, and even, if these chemicals manage to cross the placental barrier, serious problems for newborns [8]. Of the main drugs found in aquatic ecosystems are antibiotics. Antibiotics are now used in many different settings including aquaculture and livestock operations for therapeutic and treatment purposes [10,11]. Traces of antibiotics are also found in various natural environments such as aquatic ecosystems [10,11]. Of these, those belonging to the family of \(\beta\)-lactam antibiotics are the ones that appear most frequently, such as penicillin G, cephalospororin and amoxicillin (AMX), which have been found in different concentrations from ng/L to mg/L, both in surface waters and in wastewater [11]. AMX is one of the most widely used antibiotics worldwide due to its broad spectrum elimination of bacteria, both gram-positive and gram-negative. AMX prevents the synthesis of the cell wall of microorganisms is used in both human and veterinary fields [12,13]. However, due to its high demand and its continuous entry into the different wastewaters, detectable concentrations have been reported in different parts of the world. In the case of effluents from wastewater treatment plants, their concentrations vary, the highest being 1.3 mg/L and 1.6 mg/L, both detected in Hong Kong, China [14], and in Italy a magnitude of 0.013 mg/L has been found [15]. For waters used in the pharmaceutical industry, dedicated to the synthesis of this drug, concentrations around 92.2 mg/L have been found in China [16], and in drinking water sources in southeastern Brazil, a maximum concentration of 287.5 mg/L has been reported [17]. Therefore, in August 2020, the European Commission added this drug to the watch list in the field of water policy as it represents a risk both for humans and for aquatic ecosystems [18]. The generation of hydroxyl radicals, a powerful chemical agent, makes advanced oxidation processes (AOPs) an efficient option for the degradation of recalcitrant and emerging compounds [19, 20, 21], such as AMX. Among AOPs, heterogeneous photocatalysis, which involves the use of TiO\({}_{2}\) as a catalyst and UV radiation, has been widely studied. The main idea behind photocatalysis is the generation of gaps in electron pairs, which can reach and break molecular bonds [22].