Interactions Between Microplastics and Trace Metals: Ecotoxicological Implications for Tropical Marine invertebrates, Mussel Perna Perna (Linnaeus, 1758) and Sea Urchin Echinometra Lucunter (Linnaeus, 1758)

Microplastics (MPs) are recognized as emerging contaminants in marine ecosystems, not only due to their physical persistence but also for their capacity to adsorb and transport chemical pollutants, such as trace metals. In this study, we investigated the interactions between four types of virgins microplastics, like polyethylene (PE), polystyrene (PS), polypropylene (PP), and polypropylene with additives (PPa) and two trace metals, copper (Cu) and zinc (Zn), at environmentally relevant and elevated concentrations. We quantified metal adsorption using flame atomic absorption spectrophotometry and assessed the toxicological effects of MP–metal mixtures on the embryonic development of two tropical marine invertebrates: the mussel Perna perna and the sea urchin Echinometra lucunter. Our results show that metal adsorption onto microplastics was consistently higher at environmentally realistic concentrations, with PE exhibiting the highest Zn adsorption (43.16 µg·g⁻¹) and PPa the highest Cu adsorption (17.94 µg·g⁻¹). Ecotoxicological assays revealed species-specific sensitivities, with P. perna embryos showing complete developmental inhibition (0%) when exposed to Cu–Zn mixtures combined with PE or PS. E. lucunter exhibited significant developmental impairments in response to PP and PPa (76 ± 12,3%, 79 ± 16,8%), as well as selective toxicity from specific MP–metal combinations. These findings underscore the importance of polymer composition, metal speciation, and biological context in determining the toxicity of plastic-associated contaminants. The observed synergistic effects between MPs and trace metals emphasize the need to incorporate multi-stressor interactions into environmental risk assessments and regulatory frameworks addressing marine pollution.