Incubation in Wastewater Reduces the Multigenerational Effects of Microplastics inDaphnia magna

Abstract

The aging of microplastics in the environment changes their physicochemical properties. While this may affect their toxicity, comparative data on the effects of aged compared to pristine microplastics are scarce. One of those aging processes is the sorption of chemicals, which has mainly been studied for individual pollutants present in marine ecosystems. To investigate how the sorption of a complex mixture of freshwater pollutants affects the toxicity of microplastics, we incubated irregular polystyrene particles (≤63 μm) in either wastewater or ultrapure water. We exposed Daphnia magna to these aged microplastics and their pristine counterparts (80, 400, 2000, and 10,000 particles mL –1 ) over four generations using food limitation as an additional, environmentally realistic stressor. Both particle types affect the survival, reproduction, adult and neonate body lengths, and growth. An exposure to pristine microplastics results in the extinction of the third generation of daphnids. In contrast, wastewater-incubated particles induced a lower mortality. The incubation with wastewater does not change the microplastics’ size, surface charge, and structure. Consistent with the literature, we assume that the adsorption of dissolved organic matter is a key aging process reducing the toxicity of microplastics. Consequently, toxicity testing using pristine microplastics may overestimate the effects of plastic particles in nature.

Effects of microplastics mixed with natural particles onDaphnia magnapopulations

“…Additional characterization of the material and the two particles types (size distributions, surface charge, electron microscopy images etc.) can be found in Schür et al (2021) and Scherer et al (2019). Particle suspensions were prepared in Elendt M4 medium based on measured particle concentrations (Multisizer 3, Beckman Coulter) and used throughout the experiment.…”

“…Additionally, the currently available literature is strongly biased towards acute exposure scenarios, even though, due to their short generation time and the environmental persistence of microplastics, daphnids are exposed continuously over generations and not just intermittently (Rozman and Kalčikova 2021). Thus, a long-term, continuous exposure throughout an individual’s lifetime, as well as following generations, is a more realistic scenario (Schür et al 2020; 2021). Daphnids as r-strategists form large, often short-lived, populations.…”

Weathering Plastics as a Planetary Boundary Threat: Exposure, Fate, and Hazards

“…For instance, one study on plastic aging in wastewaters found no weathering-related effects of polyethylene microplastics to three aquatic test species (Daphnia magna, Danio rerio, and Lemna minor), 95 whereas another study reported decreased effects from irregularly shaped polystyrene particles to D. magna, hypothesizing that the biofilm may mitigate toxicity. 96 Potthoff et al 97 combined an aging/sieving approach to fractionate different size classes of UV-aged particles of various polymer types low in additives down to the nanorange for ecotoxicity testing. Overall, there were limited effects of the unaged vs aged particle fractions on D. magna and green algae.…”

“…From the current literature, it appears that for particles of a given size, weathering will either decrease or have a negligible influence on toxicity, in cases where the particle size distribution is not altered. For instance, one study on plastic aging in wastewaters found no weathering-related effects of polyethylene microplastics to three aquatic test species ( Daphnia magna , Danio rerio , and Lemna minor ), whereas another study reported decreased effects from irregularly shaped polystyrene particles to D. magna , hypothesizing that the biofilm may mitigate toxicity . Potthoff et al combined an aging/sieving approach to fractionate different size classes of UV-aged particles of various polymer types low in additives down to the nanorange for ecotoxicity testing.…”

Daphnia magna's Favorite Snack: Biofouled Plastics

“…Biofilm communities differ between microplastics incubated in surface waters versus wastewaters (Yang et al, 2020). Incubation in wastewater is reported to lower the toxicity of microplastics in comparison with freshwater (Schür et al, 2021). Thus, differences in ingestion between plastics from effluents or surface water might be an explanation for this.…”