Wastewater treatment plants as a source of plastics in the environment: a review of occurrence, methods for identification, quantification and fate

Plastics accumulate in the natural environment due to their durability and low recycling volumes. Wastewater treatments plants (WWTPs) have been identified as important sources for the release of plastics into aquatic and terrestrial environments that may lead to further contamination. This review provides a comprehensive summary of current knowledge on plastic pollution from WWTPs. Specifically, this article presents the current status on the sources of plastics entering WWTPs via influent, the occurrence of plastics in WWTP influent, treated effluent and sewage sludge as well as the techniques used for sampling and analysing plastics in WWTP derived samples. The fate and transfer of plastics from WWTPs to aquatic and terrestrial ecosystems is also discussed. While various studies have reported the presence of plastics in WWTP samples, which have certainly improved our level of understanding on the fate of plastics within the WWTP treatment chain, many unanswered questions still remain. A major gap is the lack of standardized methods and robust analytical techniques for the sampling, identification and quantification of plastics including nano-sized plastics in WWTP derived samples, leading to the potential underestimation of total plastics. To aid comparison of data generated by different researchers, we advocate for the harmonisation of sampling approaches, extraction methods, analytical techniques and reporting units for plastics abundance. Future studies should focus on enhanced methods that can also include estimates of nano-sized plastics.