## 1 Introduction  
The release of pharmaceutical residues (PRs) in the environment is arousing growing concern due to the significant risks posed towards humans, animals and microbial communities. Pharmaceuticals can be only partly metabolised during therapeutic use, resulting in the excretion and release of residual fractions into the sewer [1]. Then, unchanged or in the form of metabolites or conjugates, PRs reach local municipal wastewater treatment plants (WWTPs) [2]. Indeed, most medications, designed to maintain their chemical structure during the course of the therapeutic treatment, may remain active in treatment facilities for a long time [3]. Many studies have shown that most drugs are significantly recalcitrant, and conventional treatment solutions for wastewater (WW) that involve the use of anaerobic/ anoxic/oxic systems [4], oxidation ditches [5] or filters [6] are not designed to eliminate these compounds [7]. Consequently, a consistent flow of pharmaceuticals and their metabolites reach the aquatic environment, disturbing the ecological balance of rivers, lakes and other habitats and polluting groundwater, surface water and drinking water [1; 2; 3; 8; 9; 1]. Many studies have highlighted the ecological toxicity of PRs in waters environments [10; 11; 12; 13; 14; 15; 16; 17]. However, the most immediate concern regarding the release of PRs in the aquatic environment is related to the spread of antimicrobial resistance (AMR) among several classes of pathogens, first and foremost bacteria and fungi [8; 9]. Within PR compounds, antibiotics [18; 19], antifungals [19; 20; 21] and personal care products [22] play a primary role in accelerating this process. Due to the selective pressure imposed on bacteria, antibiotics particularly drive the spread of antimicrobial resistance genes in environments in which there is constant contact between the microorganisms and antimicrobials [8; 9]. Therefore, hospital and municipal WWTPs may be deemed potential hotspots for the development of AMR due to the high prevalence and persistence of PRs in WW teaming with bacteria and fungi. Antimicrobial resistance undermines the efficacy of antimicrobials, causes treatments to be unsuccessful, elongates morbidity and increases mortality [23]. According to the briefing note by the Organisation for Economic Co-operation and Development (OECD) in collaboration with the European Centre for Disease Prevention and Control (ECDC), AMR causes 33,000 mortalities and costs EUR 1.1 billion per year to the health care systems in the European Union and European Economic Areas [24]. In this context, in March 2015, the European Commission considered it necessary to resort to a new mechanism to provide high-quality monitoring information on emerging pollutants in the aquatic environment. For this purpose, the Commission under the Directive 2008/105/EC [25] on Environmental Quality Standards devised a watch list with numerous substances suspected to pose a significant threat to aquatic organisms, mammals and human health via drinking water and various pathways into the food chain [26]. Among these pollutants, several antibiotics responsible for the development of AMR, such as erythromycincin, clarithromycin, azithromycin and ciprofloxacin, found a place on the list. This systematic review aimed to collate, synthesise and critically appraise all the relevant literature on the occurrence and distribution of antimicrobial substances in WW. In particular, attention has been paid to the PRs responsible for the development of the AMR, mainly antibiotics, antifungals and personal care products commonly found in municipal and hospital WWTPs. This study intended to answer the following review question: what are the main PRs relevant for the development of AMR found in hospital and municipal WWTPs? In addition to establishing the PRs of primary concern, this work attempted to define potential correlations between the presence and concentration of PRs and certain variables across studies.