# Microbial Life on the Surface of Microlgistics in Natural Waters
## 5 Wastewater Treatment Plant Effluent as a Point Source of Microplastic  
According to the role of effluents from wastewater treatment plants (WWTPs) in the transportation of sewage-treated microorganisms into the water environment, there are different positions. It was shown that wastewater treatment plant effluent can be a source of microplastic [73; 92]. In experimental studies of [PERSON] with co-authors [73] microplastic was collected from a river not far from the point where not disinfected effluent from activated sludge plant-treated domestic water was released. It was found that microplastic was covered with dense microbial biofilm, but microscopic study showed the absence of fungal hyphae or algal cells in it. Taxonomic composition of bacterial assemblages covered microplastic differed from those from suspended organic substances and the water column. Bacterial assemblages from microplastic biofilm were less diverse, and pathogens as well as plastic degrading bacteria were more abundant in it.  
Microplastics enter WWTPs with influent and exit in sludge or effluent. It was shown for two wastewater treatment plants that microplastic from influent was accumulated in sludge (>99%), and microplastic from sludge had a more diverse spectrum of bacteria species [93; 94]. Microplastic from effluent was characterized also by the presence of opportunistic pathogenic bacteria belonging to the genus _Acinetobacter_, and bacteria was the genera _Pseudomonas_ and _Sphingomonas_ which are considered to be capable of degrading plastic. The authors showed that biofilms on microplastics within sewage have more diverse bacterial assemblages, so WWTPs can be a source of sewage-related microorganisms entered with MPs into the environment. It agrees with the results published [73; 89]. Since then, MPs from WWTPs and MPs passing through the guts of aquatic organisms have been hypothesized to play a particular role as vectors for pathogenic microorganisms [59; 73].  
Biofilms on polyethylene (PE) and polystyrene (PS) samples of microplastic placed in estuary river close to the discharge of effluent from WWTP contained bacteria from the family _Enterobacteriaceae_[86] that include several potentially pathogenic genera [95]. It was found that content of certain types of bacteria could be associated with its content in the surrounding environment, so, the highest relative abundance of _Enterobacteriaceae_ in biofilms of polystyrene microparticles in water samples with higher abundances of this family [86; 95]. The amount of fecal indicator bacteria (_Escherichia coli_ and _Enterococci_) in the biofilm colonizing polyethylene microplastic were proportionally higher in the environment influenced by sewage discharge [96]. However, it was found that only the low number of potential pathogens were attached to the microplastic particles and relative abundances of _Enterobacteriaceae_ on microplastic were significantly lower in comparison with the surrounding water communities. So, no enrichment with potential pathogens on microplastic particles was observed. However, authors concluded that due to constant long-term discharge of effluent from wastewater treatment plants into freshwater systems, attention should be given to possible increase of levels of microbial pollution [86].