Microbes with plastic-degrading and pathogenic potentials are present on plastics in the final polishing pond of a wastewater treatment plant.

We characterised plastisphere microbial communities in the polishing pond of a municipal wastewater treatment plant, applying prokaryotic 16S rRNA gene, eukaryotic 18S rRNA gene and fungal ITS2 region sequencing to identify changes in microbial biofilm community compositions over time. Pondwater and biofilm from linear low-density polyethylene (LLDPE), nylon-6 (PA), polyethylene terephthalate (PET), polylactic acid (PLA), oxo-degradable linear low-density polyethylene (OXO) and glass were sampled after 2, 6, 26 and 52 weeks of constant immersion. Microbial communities in ambient pondwater differed significantly from those forming biofilms on solid substrates. Biofilm age and depth in the water influenced microbial community compositions. However, no substrate-specific microbial communities were found among glass and plastic polymer types, regardless of artificial ageing. All substrates housed taxa associated with microbes previously reported to biodegrade plastics, being most abundant at two and 52 weeks for bacteria and fungi, respectively. Potential pathogens were found on all substrates, also being most abundant at two and 52 weeks for bacteria and eukaryotes, respectively. Our study highlights that the volume of plastics, more than its polymer form, may be most important when considering plastic's potential impacts on terrestrial and aquatic ecosystems, and for public health.