Foaming at the mouth: Ingestion of floral foam microplastics by aquatic animals

Phenol-formaldehyde plastics are used globally as floral foam and generate microplastics that can enter the environment. This study is the first to describe how aquatic animals interact with this type of microplastic, and the resultant physiological responses. We analysed "regular foam" microplastics generated from petroleum-derived phenol-formaldehyde plastic, and "biofoam" microplastics generated from plant-derived phenol-formaldehyde plastic. Regular foam and biofoam microplastics showed similar FTIR spectra. Both types of microplastics were consumed by all six invertebrate species tested: the freshwater gastropod Physa acuta, the marine gastropod Bembicium nanum, the marine bivalve Mytilus galloprovincialis, adults and neonates of the freshwater crustacean Daphnia magna, the marine amphipod Allorchestes compressa, and nauplii of the marine crustacean Artemia sp. For all species, the occurrence of ingestion was similar for regular foam and biofoam microplastics. Biofoam microplastics leached more than twice as much phenolic compounds than regular foam microplastics. The leachates from regular foam and biofoam microplastics showed the same acute toxicity to Artemia nauplii (24-h LC = 27.4 mg mL and 22.8 mg mL, respectively) and D. magna (48-h LC = 17.8 mg mL and 15.3 mg mL, respectively). However, biofoam microplastic leachate was twice as toxic to embryos of the zebrafish, Danio rerio, compared with leachate from regular foam microplastic (96-h LC = 43.8 mg mL vs 27.1 mg mL). Using M. galloprovincialis, we show that regular foam microplastic leachate and the physical presence of the microplastics exerted separate and cumulative effects on catalase (CAT) activity, glutathione-s-transferase (GST) activity and lipid peroxidation. Microplastic ingestion did not affect the activity of acetylcholinesterase (AChE). Taken together, these results show that phenol-formaldehyde microplastics can interact with a range of aquatic animals, and affect sublethal endpoints by leaching toxic compounds, and through the physical presence of the microplastics themselves.