Weathering of a micro and nanosized tire particle mixture increases ingestion and growth inhibition in larval fish and juvenile mysid shrimp

Tire erosion from driving is a major source of secondary microplastics in the ocean. Tire particles (TPs) consist of diverse components that vary depending on tire type, potentially influencing their toxicity. However, most toxicological studies have focused on single-tire types or single tire-associated chemicals, overlooking the environmental impact of multi-tire mixtures. This study investigates the behavioral and growth-related effects of environmentally relevant pristine and weathered multi-tire mixtures on two model estuarine species: the fish Inland Silverside (Menidia beryllina) and the mysid shrimp (Americamysis bahia). We exposed 5-day post-fertilization fish embryos and 7-day-old mysid shrimp to micro (1-20 μm) and nano (<1 μm) TPs at four concentrations (10, 100, 1000, and 10,000 particles/mL), as well as to pristine and weathered leachates. Both species showed significantly higher ingestion rates for weathered TPs. Effects on growth differed between species, with the most pronounced impacts observed in response to weathered TPs. Behavioral alterations also varied, with weathering increasing the toxicity of TPs in A. bahia, but not in M. beryllina. Overall, this study shows that weathered mixed TPs have a broader impact than pristine mixed TPs, and suggests greater effects than pristine particles derived from a single-tire type in A. bahia, as evidenced by comparison with a previous study. These findings emphasize the need to move beyond testing only individual tire types, to account for aged particles, and to include multiple species in toxicity assessments to better capture species-specific responses.