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.