AUTHOR=Drago Claudia , Pawlak Julia , Weithoff Guntram 

TITLE=Biogenic Aggregation of Small Microplastics Alters Their Ingestion by a Common Freshwater Micro-Invertebrate

JOURNAL=Frontiers in Environmental Science

VOLUME=Volume 8 - 2020

YEAR=2020

URL=https://www.frontiersin.org/journals/environmental-science/articles/10.3389/fenvs.2020.574274

DOI=10.3389/fenvs.2020.574274

ISSN=2296-665X

ABSTRACT=In recent years, increasing concerns have been raised about the environmental risk of microplastics in freshwater ecosystems. Small microplastics enter the water either directly or accumulate through disintegration of larger plastic particles. These particles might then be ingested by filter-feeding zooplankton, such as rotifers. Particles released into the water may also interact with the biota through the formation of aggregates, which might alter the uptake by zooplankton. In this study, we tested for size-specific aggregation of polystyrene microspheres and the effect of their ingestion by a common freshwater rotifer B. calyciflorus. The ingestion of 1-, 3- and 6-µm microspheres as the sole food intake, in association with food algae and in aggregation with biogenic matter was examined. After 72 hours incubation in pre-filtered natural river water, the majority of the 1-µm spheres occurred as aggregates. The larger the particles, the higher the relative number of single particles but the larger the aggregates. All particles were ingested by the rotifer following a Type-II functional response. The biogenic aggregation of microspheres led to a significant size-dependent alteration in their ingestion. Rotifers ingested more microspheres when exposed to aggregated 1- and 3-µm MS as compared to single spheres, whereas fewer aggregated 6-µm spheres were ingested. This suggests that the small particles when aggregated were in an effective size range for Brachionus, while the aggregated larger spheres became too large to be efficiently ingested. These observations provide the first evidence of a size- and aggregation-dependent feeding interaction between microplastics and rotifers. Microplastics when aggregated with biogenic particles in a natural environment can rapidly change their size-dependent availability. The aggregation properties of microplastics should be taken into account when performing experiments mimicking the natural environment.