No adverse effects of three size classes of UV-aged and fragmented polyethylene microplastics on life-history traits of two marine teleost fish species in standardized toxicity tests.

Microplastics (MPs) detected in marine environments exhibit substantial variability in shape, size, polymer type, and other physicochemical properties. Although numerous laboratory studies have investigated the effects of MPs on marine organisms, studies specifically examining the effects of environmentally abundant aged polyethylene (PE) MPs on the early life stages of marine fishes, using officially recognized standardized test protocols remain limited. In this study, we evaluated the effects of additive-free, ultraviolet (UV)-aged, fragmented PE MPs (afPE-MPs) in three size classes (10, 30, and 100 μm) and various concentrations on life-history traits of red seabream (Pagrus major) and mummichog (Fundulus heteroclitus) under dispersant-free exposure conditions. The exposure concentrations were based on a projected future marine concentration of 1 mg/L, with the highest level elevated by up to 30-fold. Red seabream in the embryo-hatching larval and juvenile stages, as well as juvenile mummichogs, were exposed for 4 days following the OECD Test Guideline 203. Larval mummichogs were exposed for 7 days following the Whole Effluent Toxicity (WET) test protocol or for 28 days in accordance with OECD Test Guideline 215. We found that, across all experiments, afPE-MPs did not produce any detectable effects on the survival or growth of either species or life stage. These results suggest that under dispersant-free conditions, afPE-MPs are unlikely to induce organism-level effects during the early life stages of these marine fish. This study provides important quantitative data for improving the ecological risk assessment of weathered MPs in an area where information on marine fish has been notably limited.