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The contribution of microplastics to the spread of antibiotic resistance genesduring wastewater treatment

Leonidou Evangelia

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Summary

Microplastics have been detected in wastewater treatment plants (WWTPs) as a result of human activity in modern times. Among the broad variety of pharmaceutical compounds present in wastewater, antibiotics are detected in significant concentrations, ranging from ng/L to μg/L. Microplastics contribute to the adhesion and growth of microorganisms, forming biofilm. The biofilm facilitates transmission between colonists and it contributes to the spread of antibiotic resistance genes (ARGs). As a result, municipal wastewater is one of the main sources of antibiotics and resistance genes in the environment. The release of treated wastewater into the environment and the use of treated sludge for agricultural purposes make it imperative to study the transport of ARGs associated with microplastics into the environment.The aim of this work is to determine whether the microplastics detected in a typical wastewater treatment plant contribute to the dispersion of ARGs in the aquatic environment. For this reason, samples were taken from the activated sludge and the effluent of a local wastewater treatment plant located in Chania, Crete during the hot (tourist season) and cold (non-tourist season) months in 2020. A specified number of microplastics was selected from each sample and the microbiological load attached to their surface was separated. Furthermore, additional samples were taken from the activated sludge, without any prior treatment, to isolate the total DNA and measure the total load of ARGs. The separation was followed by the qualitative and quantitative determination of polymers from the effluent samples, while the biofilm from all the samples was subjected to RT-PCR molecular analysis to detect and quantify the ARGs responsible for resistance to quinolones, β-lactams, tetracyclines and sulfonamides. Specifically, the target genes were qnrA, ampC, tetA and sul2.The main types of polymers identified were HDPE, PP and PET. Also, higher concentration of ARGs was recorded in the effluent samples compared to the activated sludge samples. This fact, raises concerns about microplastics and the transport of ARGs, as the ultimate recipient of treated wastewater is the marine environment. In addition, higher concentration of the ARGs was recorded in the samples obtained from the biofilm of the microplastics than in the samples that were not further processed. Among the four genes evaluated, ampC and tetA were detected in the most samples, indicating that β-lactams and tetracyclines are the most commonly used antibiotics in this community. Moreover, the study showed variable detection of the amount of ARGs during the sampling period. This indicates the overuse of antibiotics or wrong consumption even for viral infections.Therefore, this research contributes to the better understanding of the transport and release of ARGs through WWTPs, covering any gaps in the existing literature, with the ultimate goal of protecting the environment and sustainable development.

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