Concomitant presence of nanosized plastics and metal(loid)s: is there cause for alarm? State-of-the-art and recommendations for future studies

Nanoplastics (NPLs) accumulated in freshwater systems may serve as sinks for metal(loid)s. To date, few studies have assessed the joint effects of NPLs-metal(loid)s on freshwater biota and the risk that these mixtures may pose has not been discussed. This critical review shows that research in this context focused solely on a single polymer – polystyrene, and single shape – spherical particles, in combination with seven different metal(loid)s (copper, cadmium, chromium, zinc, lead, arsenic, and gold). The characterization of nanosized particles in such mixtures was performed mostly recurring to one single technique (DLS), often disregarding the type of test media. The effects of NPLs-metal(loid)s co-exposure are reported mainly for producers rather than consumers. Overall, co-exposure can trigger more toxic effects than exposure to either substance alone (synergism). The effects of synergism are polymer size-dependent, increasing with NPLs size decrease. These results support further research, assessing other combinations (including polymer type and shape) and organisms, to check if the pattern of synergism remains, for proper policy-making on plastic disposal evidence-based.