Urban wastewater treatment plants (UWTPs) are among the main sources of antibiotics' release into various compartments of the environment worldwide. The aim of the present paper is to critically review the fate and removal of various antibiotics in wastewater treatment, focusing on different processes (i.e. biological processes, advanced treatment technologies and disinfection) in view of the current concerns related to the induction of toxic effects in aquatic and terrestrial organisms, and the occurrence of antibiotics that may promote the selection of antibiotic resistance genes and bacteria, as reported in the literature. Where available, estimations of the removal of antibiotics are provided along with the main treatment steps. The removal efficiency during wastewater treatment processes varies and is mainly dependent on a combination of antibiotics' physicochemical properties and the operating conditions of the treatment systems. As a result, the application of alternative techniques including membrane processes, activated carbon adsorption, advanced oxidation processes (AOPs), and combinations of them, which may lead to higher removals, may be necessary before the final disposal of the effluents or their reuse for irrigation or groundwater recharge.

The spread of antibiotic-resistant bacteria is a growing problem and a public health issue. In recent decades, various genetic mechanisms involved in the spread of resistance genes among bacteria have been identified. Integrons – genetic elements that acquire, exchange, and express genes embedded within gene cassettes (GC) – are one of these mechanisms. Integrons are widely distributed, especially in Gram-negative bacteria; they are carried by mobile genetic elements, plasmids, and transposons, which promote their spread within bacterial communities. Initially studied mainly in the clinical setting for their involvement in antibiotic resistance, their role in the environment is now an increasing focus of attention. The aim of this review is to provide an in-depth analysis of recent studies of antibiotic-resistance integrons in the environment, highlighting their potential involvement in antibiotic-resistance outside the clinical context. We will focus particularly on the impact of human activities (agriculture, industries, wastewater treatment, etc.).

There is increasing evidence that human activity, and especially the resulting effluent, has a major role in the dissemination of bacterial antibiotic-resistance determinants in the environment. Hospitals are the major antibiotic consumers and thus facilitate the spread of antibiotic resistance. Questions are increasingly being raised about the management of hospital effluents, but their involvement in antibiotic-resistance dissemination has never been assessed. Integrons are a paradigm of genetic transfer between the environmental resistome and both commensal and pathogenic bacteria. In order to assess the impact of hospital activities on antibiotic-resistance dissemination in the environment, we monitored integrons and their gene cassettes in hospital effluents, and their release in the environment. We found that bacterial communities present in a hospital effluent contained a high proportion of integrons. In terms of both their gene cassette diversity and gene cassette arrays, the urban effluent and municipal wastewater treatment plant (WWTP) influent were most similar, whereas the hospital effluent and recirculation sludge exhibited very specific patterns. We found that anthropogenic activities led to the release of abundant integrons and antibiotic-resistance gene cassettes, but we observed no specific impact of hospital activities on the receiving environment. Furthermore, although the WWTP did not reduce the normalized integron copy number, it reduced the diversity of gene cassette arrays contained in the raw wastewater, underlining the effect of the biological treatment on the anthropogenic integron pool arriving at the WWTP.