pseudofeces production and reduced filtering activity have been reported.20 For algae, nanoplastic has been shown to reduce CO2 uptake and enhance the production of reactive oxygen species (ROS).21 As the interaction of organisms with pollutants in particulate form is completely different from that with conventional dissolved chemicals, there is a potential high risk associated with particles.7,22 Given the limited data, there is an urgent need to quantify the effects of nanoplastic on freshwater organisms. Effects of nanoplastic may be related to particle toxicity, toxicity of plastic-associated chemicals, or both and will depend on the characteristics of the nanoplastic, such as particle size, polymer type, and age. However, previous research on nanoparticle behavior and effects was often conducted using pristine particles,23 whereas aged and naturally altered particles are of higher importance considering environmental relevance, which will therefore be addressed in the present study.