Ultraviolet Radiation Enhances the Toxicity of Tire Wear Particle Leachate to Early Life Stages of Red Drum (Sciaenops ocellatus) & Southern Flounder (Paralichthys lethostigma).

Tire wear particles (TWP) that runoff into aquatic habitats are linked to fish kills in urbanized watersheds of the Pacific Northwest. These TWP leach complex chemical mixtures, including photodynamic compounds that can become orders of magnitude more toxic under solar radiation. This enhancement is especially relevant for transparent aquatic organisms in high-solar environments, such as Gulf of Mexico (GoM) estuaries that provide critical nursery habitats for recreationally and ecologically valuable early life stage (ELS) fishes. Yet data on TWP contamination and photoinduced toxicity in these systems remain limited. Using a fully factorial design, we exposed ELS red drum (Sciaenops ocellatus) and southern flounder (Paralichthys lethostigma) to TWP leachate under ambient indoor lighting or simulated solar radiation (as UV-A). Sensitivity was species-specific and dependent on UV coexposure. Red drum mortality increased independently with dose and UV, while southern flounder were sensitive regardless of UV. Sublethal impacts were mixed: red drum showed reduced growth, altered energy utilization, and diminished development under UV, whereas southern flounder showed reduced size and significant pericardial edema regardless of UV. These results demonstrate that TWP toxicity is species-specific and mediated by both phototoxic and nonphototoxic mechanisms, highlighting the vulnerability of ELS fishes in critical nursery habitats.