Polyethylene microplastics enhance metal(loid)s toxicity and accumulation in the marine rotifer Proales similis

Chemical mixtures pose a significant environmental challenge, as interactions among pollutants amplify their detrimental effects on ecosystems, and the knowledge of marine and tropical/subtropical species is scarce. We examine the acute and chronic effects of polyethylene microplastics (PE-MPs) and As, Cd, Cu, and Pb in pairwise combinations on the growth rate (PGR) and accumulation of metal(loid)s on the marine rotifer Proales similis a promising species for ecotoxicological assessment in tropical environments. The 48-h EC of PE-MPs (1-4 μm) was determined, and chronic reproduction tests were performed by combining 25 and 250 μg L of PE-MPs with metal(loid)s at two realistic environmental concentrations: 10 and 100 μg L As, Cd, and Pb, and 1.0 and 10 μg L Cu. The EC of PE-MPs was 4.62 mg L. In most cases, the PGR was significantly lower in the mixture treatments than in the individual exposures to the metal(loid)s or PE-MPs. Predicted effects were greater than the observed effects, indicating synergism in all the tested mixtures. The concentration of As, Cd, Cu, and Pb increased when PE-MPs were present. These results highlight the potential of PE-MPs to act as vectors for metal(loid)s and reveal the synergistic effects of MP-metal(loid) mixtures at environmentally relevant concentrations. The marine, non-selective filter-feeding rotifer P. similis, used as our model organism, demonstrates promise as a tool for risk assessment in tropical environments.