## 1 Introduction
Pharmaceutically active contaminants might pose serious threats to ecosystems and wildlife, since they can induce antimicrobial resistance, act as endocrine disruptors, and impair reproduction, particularly in fish populations [30]. Serious declines in scavenger species, such as valture populations in South Asia due to their consumption of diclofenac-treated livestock, have also been reported [31; 32]. Likewise, humans are exposed to pharmaceuticals through contaminated drinking water and by ingesting the residues that accumulate in fish, meat, dairy products, and plant crops [33]. In this context, the idea of the re-valorization of unused or expired drugs for corrosion control can offer a potential solution to several major environmental and economic challenges, i.e., reducing environmental pollution with pharmaceutically active compounds and lowering the disposal costs of pharmaceuticals wastes [34]. A perusal of the literature revealed that numerous drugs have been investigated as corrosion inhibitors [18; 35; 36; 37] for various metallic materials based on iron [38; 39; 40; 41; 42; 43; 44], aluminum [45; 46; 47], copper [34; 48; 49; 50; 51; 52; 53; 54], or zinc [55; 56; 54] in different environments, while only limited research is available on copper alloys [57; 58]. Additional information on the effectiveness of several pharmaceuticals reported as corrosion inhibitors of different metallic materials is provided in Table S1 in the Supplementary Materials. The aim of the present paper is to evaluate the properties of an expired drug, named _Fluimucil_, as a green corrosion inhibitor for bronze in two corrosive environments, namely 3.5 wt.% NaCl solution and simulated acid rain of a pH = 3.4 typical of a highly polluted urban atmosphere. The active ingredient in _Fluimucil_ is N-acetyl cysteine (NAC), which is a safe and inexpensive drug [59], approved by the U.S. Food and Drug Administration,and recognized by the World Health Organization as an essential medicine. N-acetyl cysteine is widely used as primary antidote for acetaminophen (paracetamol) overdose and, in recent years, as mucolytic agent in respiratory diseases [60]. It also has antioxidant, anti-inflammatory, antibacterial, anticancer, and neuroprotective properties [61; 60]. According to our recent search, there are no reported data available in the literature on the use of NAC-containing drugs as corrosion inhibitors for metals. However, it should be mentioned that synthetic N-acetyl cysteine has previously been reported as an effective inhibitor for the corrosion of steel in 15% HCl solution [62], C-steel in 1 M HCl [63], and copper [50] and Cu-10 Al-5 Ni [64] in NaCl solution. The corrosion inhibition mechanism of the proposed drug for bronze in the two corrosive environments was examined using electrochemical techniques (potentiodynamic polarization and electrochemical impedance spectroscopy) and surface analysis through scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM-EDX). Various adsorption isotherms were also tested to determine their potential relevance in explaining the adsorption behavior of the drug on the bronze surface.