Microplastics increase impact of treated wastewater on freshwater microbial community

Plastic pollution is a major global concern with several million microplastic particles entering every day
freshwater ecosystems via wastewater discharge. Microplastic particles stimulate biofilm formation
(plastisphere) throughout the water column and have the potential to affect microbial community
structure if they accumulate in pelagic waters, especially enhancing the proliferation of biohazardous
bacteria. To test this scenario, we simulated the inflow of treated wastewater into a temperate lake using
a continuous culture system with a gradient of concentration of microplastic particles. We followed the
effect of microplastics on the microbial community structure and on the occurrence of integrase 1 (int1),
a marker associated with mobile genetic elements known as a proxy for anthropogenic effects on the
spread of antimicrobial resistance genes. The abundance of int1 increased in the plastisphere with
increasing microplastic particle concentration, but not in the water surrounding the microplastic particles.
Likewise, the microbial community on microplastic was more similar to the original wastewater
community with increasing microplastic concentrations. Our results show that microplastic particles
indeed promote persistence of typical indicators of microbial anthropogenic pollution in natural waters,
and substantiate that their removal from treated wastewater should be prioritised.
© 2017 Elsevier Ltd.