Limited multigenerational effects of polypropylene microplastics predominantly sized 100-200µm in medaka.

Microplastics are ubiquitous in aquatic environments; however, information on their multigenerational effects remains limited, particularly for environmentally relevant polymers such as polypropylene (PP). In this study, we evaluated the biological effects of PP microplastics through a multigenerational exposure experiment using medaka (Oryzias latipes), a model species for ecotoxicological assessment. Endpoints directly related to population sustainability, including embryonic development, growth, reproduction, and sexual differentiation, were examined across generations. PP particles, predominantly within the 100-200 μm size range, were consistently detected in the digestive tracts of exposed fish at multiple developmental stages, confirming continuous ingestion. Despite this, no significant effects were observed on fecundity, fertilization rate, hatching success, growth, or sexual differentiation across generations. These findings suggest that continuous multigenerational exposure to PP particles of the tested size range does not adversely affect the evaluated life-history traits associated with population maintenance. To contextualize these findings, environmental concentrations of microplastics in Suruga Bay were quantified using pyrolysis gas chromatography-mass spectrometry (Py-GC/MS). PP was detected at selected sites, with concentrations up to 6.69 μg/L, whereas other polymers, such as polyvinyl chloride (PVC), were more widely distributed and exhibited higher concentrations. The spatial variability of PP suggests localized contamination sources rather than uniform distribution. Taken together, these results suggest that PP microplastics, predominantly within the 100-200 μm size range, did not result in measurable adverse effects on the evaluated developmental and reproductive endpoints in medaka under the tested conditions. This study provides new insights into the ecological risks of microplastics by integrating multigenerational toxicity data with quantitative environmental exposure assessment.