Drivers of microplastic toxicity on Daphnia magna

, Zimmermann Lisa, Wagner Martin, Völker Carolin.

Microplastics are a heterogeneous set of materials that differ not only in particle properties, like size and shape, but also in chemical composition, including polymers, additives and side products. Thus, we were interested in the driving factor of microplastic toxicity: Is it the chemicals or the particle itself? To address this question, we chronically exposed Daphnia magna to three types of irregular microplastics, polyvinyl chloride (PVC), polyurethane (PUR) and polylactic acid (PLA) microplastics as well as to natural kaolin particles, ¡ 59 µm. First, we compared the toxicity of the different materials by exposing the daphnids to high concentrations of particles (10, 50, 100, 500 mg/L). To investigate the drivers of toxicity, we used four exposure scenarios, including the original microplastics and microplastics from which we removed the extractable chemicals as well as the compounds extracted or migrating from the plastics to differentiate between chemical and particle toxicity. All tested microplastics negatively affected the life-history of D. magna. Exposure to PVC had the strongest effect on daphnid reproduction, PLA significantly reduced the survival. Thus, the toxicity of microplastics depends on the endpoint and the material. In addition, the results indicate that bio-based and biodegradable plastics can be as toxic as their conventional counterparts. Microplastics were more toxic than the natural particle kaolin when comparing numerical concentrations. Importantly, the contribution of plastic chemicals to the toxicity was also plastic type-specific. Plastic chemicals were the main driver for toxicity in case of PVC but not PUR and PLA microplastics. Our findings highlight that microplastics are not created equal: Multiple plastic types as well as their chemical composition need to be taken into account when assessing their environmental hazards. In addition, ecotoxicological research needs to move forward to investigating the impacts of so far understudied polymers, such as PVC, PUR and “bioplastics”.

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