Solar-assisted Advanced oxidation processes affect the antibiotic resistance traits of bacteria developed in wastewater-irrigated soils: Are they a friend, a foe, or just a traitor in our midst?

• Solar/Fe/PMS was the most effective AOP, proving to be a trusted friend in bacterial inactivation. • The MICs of antibiotics increased post-treatment, revealing a foe in the AOP-induced resistance traits. • Inadvertent antibiotic presence enhanced disinfection but raised concerns over resistance. • Wastewater irrigation pressures bacteria, fostering controversial traits such as antibiotrophy. • AOPs disinfect but may act as a traitor, promoting resistant bacteria and urging safety assessments. This study investigated the effects of solar-assisted Advanced Oxidation Processes (AOPs) on the antibiotic resistance traits of bacteria developed in wastewater-irrigated soils. Bacteria were extracted from three soil sites with varied temporal exposure to treated wastewater (TWW): non-irrigated soil (S1), soil irrigated for 5 years (S2), and soil irrigated for 25 years (S3). The efficacy of solar light alone ( hv ), hv /Fe 2+ /H 2 O 2 , hv /Fe 2+ /PMS, and hv /Fe 2+ /PDS processes in inactivating the bacterial consortia was examined. Disinfection efficacy and post-disinfection events, including bacterial regrowth, the role of antibiotics present in the matrix, and shifts in minimum inhibitory concentrations (MICs) over the three selected solar AOP cycles were assessed. These AOPs completely inactivated the bacteria, with hv /Fe 2+ /PMS being the most effective, followed by hv /Fe 2+ /H 2 O 2 and hv /Fe 2+ /PDS, respectively. The presence of antibiotics during treatment enhanced disinfection, suggesting a reduction in resistance. However, post-treatment regrowth was observed, with solar/Fe/PMS being the most effective treatment at limiting regrowth. After three treatment cycles, the MICs of ampicillin, tetracycline, kanamycin, and streptomycin increased, indicating that surviving antibiotic-resistant bacteria retained their phenotype after multiple solar-AOP exposures and formed resistant subpopulations. TWW irrigation was responsible for the development of antibiotic resistance; however, bacteria developed antibiotic breakdown strategies, including bio-assimilation (antibiotrophy). While concerning from a safety perspective, this knowledge can facilitate the development of effective antibiotic biodegradation strategies. Finally, although our solar AOPs are essentially a friend, effective for disinfection, our findings indicate that tertiary/quaternary treatments may inadvertently contribute to shifts in bacterial community assemblies and the development of antibiotic resistance and new phenotypes in surviving populations, thus capable of treason, highlighting the need for comprehensive post-treatment safety assessments.