Enantioselective degradation of amphetamine-like environmental micropollutants (amphetamine, methamphetamine, MDMA and MDA) in urban water

Amphetamine-like compounds undergo stereoselective degradation during wastewater treatment and in receiving waters, with microbial processes favoring the S-(+)-enantiomer over the R-(-)-enantiomer. In controlled laboratory microcosms simulating activated sludge, all four compounds—amphetamine, methamphetamine, MDMA, and MDA—showed preferential breakdown of the S-(+)-enantiomer, while R-(-)-enantiomers remained largely undegraded, indicating greater persistence. Amphetamine was the most biodegradable, followed by MDMA and methamphetamine. Photochemical processes degraded MDMA and methamphetamine but were not stereoselective. Biodegradation of S-(+)-methamphetamine produced S-(+)-amphetamine, and racemic MDMA degraded stereoselectively in activated sludge, enriching R-(-)-MDMA and forming S-(+)-MDA. Only mild stereoselectivity occurred during MDMA degradation in river water, likely due to different microbial communities. Kinetic studies confirmed MDMA's recalcitrance.

Study at a glance

Abstract

This paper aims to understand enantioselective transformation of amphetamine, methamphetamine, MDMA (3,4-methylenedioxy-methamphetamine) and MDA (3,4-methylenedioxyamphetamine) during wastewater treatment and in receiving waters. In order to undertake a comprehensive evaluation of the processes occurring, stereoselective transformation of amphetamine-like compounds was studied, for the first time, in controlled laboratory experiments: receiving water and activated sludge simulating microcosm systems. The results demonstrated that stereoselective degradation, via microbial metabolic processes favouring S-(+)-enantiomer, occurred in all studied amphetamine-based compounds in activated sludge simulating microcosms. R-(-)-enantiomers were not degraded (or their degradation was limited) which proves their more recalcitrant nature. Out of all four amphetamine-like compounds studied, amphetamine was the most susceptible to biodegradation. It was followed by MDMA and methamphetamine. Photochemical processes facilitated degradation of MDMA and methamphetamine but they were not, as expected, stereoselective. Preferential biodegradation of S-(+)-methamphetamine led to the formation of S-(+)-amphetamine. Racemic MDMA was stereoselectively biodegraded by activated sludge which led to its enrichment with R-(-)-enantiomer and formation of S-(+)-MDA. Interestingly, there was only mild stereoselectivity observed during MDMA degradation in rivers. This might be due to different microbial communities utilised during activated sludge treatment and those present in the environment. Kinetic studies confirmed the recalcitrant nature of MDMA.