Synergistic transgenerational reproductive toxicity of polystyrene nanoplastics and butylparaben at NOAEL levels via SET-2–mediated H3K4me3 modification in Caenorhabditis elegans

Emerging contaminants such as polystyrene nanoplastics (PS-NPs) and butylparaben (BuP) frequently co-occur in surface waters and sediments, raising concerns about mixture risks at environmentally relevant doses. Although each compound is non-effective at its individual no-observed-adverse-effect level (NOAEL), their joint long-term impacts remain insufficiently defined. Here, we used Caenorhabditis elegans as a multigenerational in vivo model to test whether maternal co-exposure to PS-NPs and BuP at NOAELs induces heritable reproductive toxicity. Maternal co-exposure reduced reproductive outcome and increased germline apoptosis across four generations. Bliss independence analysis indicated a synergistic interaction. Mechanistically, co-exposure elevated intestinal reactive oxygen species (ROS) and increased embryonic histone H3K4 trimethylation (H3K4me3). Notably, reproductive impairments and H3K4me3 elevation were absent in set-2 mutants, indicating that SET-2-mediated H3K4 trimethylation is essential for transmitting transgenerational toxicity. Our findings underscore the limitations of single compound NOAEL-based assessments and support incorporating epigenetic biomarkers and transgenerational endpoints into chemical risk evaluation frameworks.