Stream biofilms are hotspots of nutrient cycling driving major ecosystem processes. Microplastic (MP) is an ubiquitious pollutant in the aquatic environment, with highly divers physical and chemical properties.  Here we hypothesised that i) biofilms can act as sink for MP in streams ii) that MP induce changes of biofilm properties, and that iii) MP can act as pointsource of chemicals. Sampling in the river Ter (NE Spain) showed significant presence of MP in biofilms, confirming their role as major sink for MP. Combining a variety of novel techniques, we study the consequences of incorporation of MP in biofilm. Using microcoms experiments, we compared biofilms incorporating spherical polyethylene MP with either native/weathered surface structure (Surf-MP) or coated with Tricolsan (TCS-MP). All MP were incoroporated into the biofilm matrix with no effect on biomass accumulation, photosynthetic yield, and respriation. Yet, the exposures to MP induced a significant shift in microbials community composition. In contrast, while similar in exposures to MP, nutrient uptake rates were lower in biofilm exposed to TCS-MP. Mechanical properties measured in biofilm exposed to Surf-MP indicated higher stiffness upon MP expsure and biofilm spatial species organization measured in biofilm exposed to TCS-MP resulted to be significantly altered as a response to Triclosan on the MP surface. Our results confirm the fundamental role of biofilms as sink of MP and indicate that MP heavily impact biofilm structure, function and dislodgement behavior.

Primary Presenter: Stephanie Merbt, CEAB.CSIC (stephanie.merbt@ceab.csic.es)

Authors:

Alexandra Kroll, Centre Ecotox, Switzerland  (Alexandra.Kroll@oekotoxzentrum.ch)

Davide Ciccarese, University of Lausanne, Switzerland  (davidec@mit.edu)

Manu Tamminen, University of Turku, Finnland  (manu.tamminen@utu.fi)

Patrick Rührs, ETH Zürich  (pat.ruehs@gmail.com)

Linn Sgier, EAWAG, Switzerland  (Linnsgier@gmail.com)

Helena Guasch, Ceab.CSIC  (helena.guasch@ceab.csic.es)

Eugenia Marti, CEAB.CSIC  (eugenia@ceab.csic.es)

Ahmed Tlili, University of Zürich, Switzerland  (ahmed.tlili@eawag.ch)

Kristin Schirmer, EAWAG, Switzerland  (Kristin.schirmer@eawag.ch)

Renata Behra, EAWAG, Switzerland  (renata.behra@eawag.ch)