Microplastics are widely distributed in aquatic environments. The term ‘microplastics’ encompasses a wide array of particles with unique polymer constituents, morphologies, and sources, such as automobile tire tread. Tire wear particles (TWP) can end up in waterways near densely populated municipalities, where they can interact with aquatic biota. Studying the impact of commonly detected synthetic particles such as TWP, across micro and nanoscopic sizes, on estuarine indicator species may tell us how these anthropogenic contaminants affect the entire ecosystem. This study investigated ingestion, growth, and behavioral responses of inland silversides (Menidia beryllina) and mysid shrimp (Americamysis bahia) when exposed to three concentrations of TWP (60, 6000, and 60,000 particles/mL which is equivalent to 0.0038, 0.0378 and 3.778 mg/L in mass concentration for micro size particles) at micro and nano size fractions with TWP leachate across 5-25 practical salinity unit (PSU) salinity gradient. Following exposures, M. beryllina and A. bahia had significantly altered swimming behaviors, such as freezing, in zone duration and total distance moved, that could lead to an increased risk of predation and foraging challenges in the wild. Both A. bahia and M. beryllina growth was reduced in a concentration dependent manner when exposed to micro TWP, whereas M. beryllina demonstrated reduced growth only when exposed to nano TWP. TWP internalization was observed in both taxa at 15 PSU. A. bahia and M. beryllina had significantly higher particle ingestion at 15 PSU following micro TWP exposure. The presence of adverse effects in M. beryllina (growth at micro TWP and behavior) and A. bahia (behavior) indicate that even at current environmental levels, which are expected to continue to increase, aquatic ecosystems are likely experiencing negative impacts from TWP pollution
