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The EU plastic strategy aims to reduce the environmental impact of the increasing plastic production, by replacing petrochemical-based polymers with biodegradable ones. But this mitigation measure for the plastamination might, in turn, generate bio-based microplastics in environments that are not necessarily safe. Biodegradable and non-biodegradable plastics, polylactic acid (PLA) and polypropylene (PP) respectively, and their leachates were used for testing microplastic (MP) effects on seven marine species from different trophic levels, including bacteria, algae, rotifers, copepods, amphipods and branchiopods. Results highlighted the toxic effects of both MPs for three consumers, but no toxicity for decomposers and primary producers. Leachates did not induce negative effects for five species tested. A dose-dependent toxic effect of both PP and PLA on different life stages of A. franciscana was observed, with more advanced stages being more sensitive to MPs in terms of mortality. Molecular analysis revealed increased mRNA levels of Heat shock proteins in A. franciscana metanauplii and adults, suggesting their role in oxidative stress response, and decreasing in juveniles, indicating potential irreversible damage. These results indicated that PLA and PP might have comparable ecotoxicological impacts, raising concerns about the effectiveness of biodegradable polymers in mitigation plastic pollution. The study also emphasizes the importance of considering different trophic levels, life stages, and feeding strategies when evaluating the toxic effects of MPs from a One Health perspective., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2025 Elsevier B.V. All rights reserved.)

The increasing demand for sustainable alternatives to conventional plastics has propelled the interest in bioplastics. A few papers reported on the effects of plastics on crustaceans, but no indication about biodegradable polymers is available. Hippolyte inermis Leach, 1816 is a protandric shrimp commonly living on leaves of the seagrass Posidonia oceanica, in the Mediterranean Sea. This crustacean is typically chosen as a model to study sex differentiation processes. Here, we demonstrated its convenience as a model organism to study the effects of biodegradable polymers (BPs). Five BPs were studied: polybutylene succinate (PBS), polybutylene succinate-co-butylene adipate (PBSA), polycaprolactone (PCL), poly-3-hydroxybutyrates (PHB) and polylactic acid (PLA). Larvae of H. inermis were exposed to three concentrations of each BP (1, 5 and 10 mg/L, respectively) for ten days. After exposure, the expression levels of eighteen genes involved in stress response and detoxification processes, retrieved from a H. inermis transcriptomic library, were validated by Real Time qPCR. This study is the first using a molecular approach to detect H. inermis responses to contaminants and in particular to biodegradable polymers, through the evaluation of functional gene's pathways., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2025. Published by Elsevier B.V.)