Sources of micro(nano)plastics and interaction with co-existing pollutants in wastewater treatment plants

Wastewater treatment plants (WWTPs) are the important source of micro(nano)plastics (MNPs) and pollutants (e.g. chemicals, antibiotic resistance genes (ARGs) and pathogens) in natural environment, where the interaction in these co-existing substances has become an increasing concern. This work outlines the sources of MNPs and their interaction with pollutants in WWTPs, and assesses the potential risks after being discarded into natural environment. The sources of MNPs in WWTPs mainly include personal care products, washing clothes, surface runoff and atmospheric deposition as well as the inherent plastic equipment in WWTPs. MNPs can interact with various pollutants including ARGs and microorganisms, and organic and inorganic chemicals such as persistent organic pollutants antibiotics, and metals mainly through pi-pi, hydrophobic, electrostatic and hydrogen-bonding interactions and biofilm formation. Additionally, the WWTP conditions (e.g. pH, temperature) and components (e.g. dissolved organic matter, salinity and suspended particulates) can affect the interaction processes by modifying the sorption sites of MNPs and changing the property of MNPs and pollutants. Once being discharged into natural media, the individual and joint toxicological impacts of MNPs and associated pollutants to organisms via ingestion would be induced. As for the knowledge gap, more attentions should be focused on the contribution in various sources of MNPs and their interaction (especially submicron- to micron-size ranges) with ARGs, to improve understanding of the sources and pollution of MNPs and the combined risk with pollutants in natural environment.