A critical review of the current environmental risks posed by the antidiabetic Metformin and the status, advances, and trends in adsorption technologies for its remediation

The consumption of the antidiabetic drug Metformin (MTFN) has escalated over the last years due to the worrisome modern sedentary lifestyle. Since MTFN is not metabolized, it reaches several environmental compartments, imposing risks to aquatic organisms and possible future public health issues. Therefore, the use of adsorption as a low-cost and highly versatile mass transfer process has been proposed for its remediation and environmental control. This review presents, discusses, and compares the efficiencies reached by all adsorbents prepared and employed in MTFN adsorption. We carefully addressed the interaction mechanisms, adsorption kinetics, equilibrium modeling, and the most relevant thermodynamic parameters, creating a guide of solutions to practical problems. By comparing the data on its toxicity and controversial endocrine-disrupting effects reported in the literature with self-performed quantitative structure-activity relationship (QSAR) analysis, it was possible to see that MTFN is indeed adequately classified under the highest toxicity class, contrarily to the claims of various studies. Thus, according to the research gaps, possibilities, and challenges in the field, there is much yet to be understood and developed toward MTFN thorough removal by adsorption, such as i) the need for studies under continuous systems, ii) mechanism elucidation employing computational tools, and iii) adsorption coupled to environmental catalysis.