Effects of microplastics mixed with natural particles on Daphnia magna populations

Christoph Schür; Joana Beck; Scott Lambert; Christian Scherer; Jörg Oehlmann; Martin Wagner

doi:10.1016/j.scitotenv.2023.166521

Effects of microplastics mixed with natural particles on Daphnia magna populations

Sci Total Environ. 2023 Dec 10:903:166521. doi: 10.1016/j.scitotenv.2023.166521. Epub 2023 Aug 26.

Authors

Christoph Schür¹, Joana Beck², Scott Lambert², Christian Scherer³, Jörg Oehlmann², Martin Wagner⁴

Affiliations

¹ Department of Environmental Toxicology, Eawag, Überlandstrasse 133, 8600 Dübendorf, Switzerland; Department Aquatic Ecotoxicology, Faculty of Biological Sciences, Goethe University, Frankfurt am Main, Max-von-Laue-Str. 13, 60438 Frankfurt am Main, Germany.
² Department Aquatic Ecotoxicology, Faculty of Biological Sciences, Goethe University, Frankfurt am Main, Max-von-Laue-Str. 13, 60438 Frankfurt am Main, Germany.
³ Department Aquatic Ecotoxicology, Faculty of Biological Sciences, Goethe University, Frankfurt am Main, Max-von-Laue-Str. 13, 60438 Frankfurt am Main, Germany; Federal Institute of Hydrology, Department Biochemistry and Ecotoxicology, Am Mainzer Tor 1, 56002, Koblenz, Germany.
⁴ Department of Biology, Norwegian University of Science and Technology, Høgskoleringen 5, 7491 Trondheim, Norway. Electronic address: martin.wagner@ntnu.no.

PMID: 37640069
DOI: 10.1016/j.scitotenv.2023.166521

Abstract

The toxicity of microplastics on Daphnia magna as a key model for freshwater zooplankton is well described. While several studies predict population-level effects based on short-term, individual-level responses, only very few have validated these predictions experimentally. Thus, we exposed D. magna populations to irregular polystyrene microplastics and diatomite as natural particle (both ≤63 μm) over 50 days. We used mixtures of both particle types at fixed particle concentrations (50,000 particles mL^-1) and recorded the effects on overall population size and structure, the size of the individual animals, and resting egg production. Particle exposure adversely affected the population size and structure and induced resting egg production. The terminal population size was 28-42 % lower in exposed compared to control populations. Interestingly, mixtures containing diatomite induced stronger effects than microplastics alone, highlighting that natural particles are not per se less toxic than microplastics. Our results demonstrate that an exposure to synthetic and natural particles has negative population-level effects on zooplankton. Understanding the mixture toxicity of microplastics and natural particles is important given that aquatic organisms will experience exposure to both. Just as for chemical pollutants, better knowledge of such joint effects is essential to fully understand the environmental impacts of complex particle mixtures. ENVIRONMENTAL IMPLICATIONS: While microplastics are commonly considered hazardous based on individual-level effects, there is a dearth of information on how they affect populations. Since the latter is key for understanding the environmental impacts of microplastics, we investigated how particle exposures affect the population size and structure of Daphnia magna. In addition, we used mixtures of microplastics and natural particles because neither occurs alone in nature and joint effects can be expected in an environmentally realistic scenario. We show that such mixtures adversely affect daphnid populations and highlight that population-level and mixture-toxicity designs are one important step towards more environmental realism in microplastics research.

Keywords: Mixture toxicity; Particulate matter; Population dynamics; Suspended matter; Suspended solids.