Alistair Boxall

Plastic pollution is widespread throughout aquatic environments globally, with many organisms known to interact with and ingest plastic. In marine environments, microbial biofilms that form on plastic surfaces can produce the odorous compound dimethyl sulfide (DMS), which is a known foraging cue. This has been shown to increase the ingestion of plastic by some invertebrates and therefore act as a biological factor which influences the risks of plastic to marine ecosystems. In freshwater however, the production of DMS has been largely overlooked, despite the known sensitivity of some freshwater species to this compound. To address this gap, the present study analyzed the production of DMS by biofilms which formed on low‐density polyethylene and polylactic acid films after 3 and 6 weeks of submersion in either a rural or an urban United Kingdom river. Using gas chromatography–mass spectrometry, the production of DMS by these biofilms was consistently identified. The amount of DMS produced varied significantly across river locations and materials, with surfaces in the urban river generally producing a stronger signal and plastics producing up to seven times more DMS than glass control surfaces. Analysis of biofilm weight and photosynthetic pigment content indicated differences in biofilm composition across conditions and suggested that DMS production was largely driven by nonphotosynthetic taxa. For the first time this work has documented the production of DMS by plastic litter after submersion in freshwater rivers. Further work is now needed to determine if, as seen in marine systems, this production of DMS can encourage the interaction of freshwater organisms with plastic litter and therefore operate as a biological risk factor in the impacts of plastic on freshwater environments. Environ Toxicol Chem 2024;00:1–12. © 2024 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.