Microplastics – plastic particles less than five millimetres in diameter – can be found in oceans, lakes and rivers worldwide. It has been estimated that over 21,000 tonnes of microplastics are floating in the world’s seas. Most of these materials degrade very slowly; they are ingested by many aquatic organisms and can accumulate along the food chain. Though little is known about their ecotoxicological effects, laboratory studies have shown that ingestion of microplastics is associated with reduced filtering activity in mussels, lower feeding rates in zooplankton, and increased mortality and reduced reproduction in copepods. The current state of knowledge on microplastics in the environment is summarized in a new information sheet (available in French/German) issued by the Eawag/EPFL Ecotox Centre. It gives details of the occurrence of microplastics, the sources of inputs to aquatic ecosystems, the identification and quantification of microplastic particles, their degradation and their impacts on aquatic organisms.