Nanoparticle-specific and chemical-specific effects of tire wear particle leachate on amphibian early life stages

Tire wear particles (TWP) have been identified as a potentially toxic form of plastic in the environment. The exact mechanisms of toxicity of TWP are poorly understood, especially the possibility of specific toxicity pathways due to nanoparticles and leached chemicals. The amphibian Silurana tropicalis was exposed to stock dispersions of different fractions of TWP leachate (nanoparticles and leached chemicals; leached chemicals; nanoparticles) during its early development for 60 h and 9 days, and endpoints such as mortality, malformations and behavior were recorded. In the 60-h exposure, individuals were exposed to treatments ranging from 0-100% of the stock dispersions. The nanoparticle fraction caused a significant decrease in larval survival at all concentrations. The proportion of malformed tadpoles and tail abnormalities were impacted by all fractions, but fractions containing leached chemicals exhibited more head, gut, and edema malformations. For the 9-day exposure, individuals were exposed to treatments ranging from 0-10% of the stock dispersions. At almost all concentrations, survival was significantly reduced. Tadpoles exposed to the nanoparticle fraction had significantly larger brains. Tadpoles in fractions containing leached chemicals swam significantly less in the 10% treatment. These results reveal particle-specific and chemical-specific effects of TWP leachate which may have negative repercussions at the population level. The mechanisms of toxicity of tire wear particle leachate are currently poorly understood, especially in freshwater organisms. Our study sheds light on the differing toxicities of the nanoparticulate and dissolved chemical constituents of tire wear particle leachate on a highly relevant model amphibian, Silurana tropicalis. Leached tire wear chemicals, tire wear nanoparticles, and their mixture affected survival and physiologically relevant endpoints of the larval amphibian such as malformations, swimming behavior and brain morphometry, which can lead to adverse impacts at the population and ecosystem levels. The physiological impacts varied for the different tire wear leachate fractions, suggesting that the environmental impacts may vary with the weathering conditions and the dispersal patterns of dissolved and nanoparticulate species of tire wear leachate