Aquatic toxicity of chemically defined microplastics can be explained by functional additives.

A novel, systematic approach to relate plastic toxicity with chemical composition is undertaken. Using industrial methods, three petroleum-based polymers, low-density polyethylene (PE), polyvinyl chloride (PVC), and polyamide (PA), and the biopolymer polyhydroxybutyrate (PHB) were manufactured in different formularies including conventional and alternative additives, and microplastics of two sizes (<250 and <20 µm) were obtained with the aim to relate their composition with environmental impact in aquatic environments. Internationally accepted standard tests of regulatory use with marine organisms representative of microalgae (Tisochrysis lutea population growth), crustaceans (Acartia clausi larval survival), and echinoderms (Paracentrotus lividus sea-urchin embryo test) support the following conclusions. Aquatic toxicity of microplastics made from conventional oil-based polymers is due to leaching of chemical additives, and not to ingestion of microplastics. Use of alternative formulations based on natural rather than synthetic chemical additives did not consistently reduce aquatic toxicity except for the replacement of triclosan by the alternative biocide lawsone. In contrast, the biopolymer tested, PHB, seemed to impact marine plankton through different mechanisms associated to the higher abundance of plastic particles within the nanometric range found in this resin and absent in other materials.