Developing a New Approach Methodology Framework to Assess Biological Responses to Nanoplastics: Insights from Polystyrene and Biodegradable Particles

The widespread presence of micro- and nanoplastics (MNPs) in the environment represents an emerging risk for human and environment health. New Approach Methodologies (NAMs) offer valuable tools to improve the mechanistic understanding of nanoscale processes and support hazard identification without animal testing. This study investigated the biological effects of exposure to 0–100 µg/mL 100 and 20 nm polystyrene (PS-NPs) and 100 nm polycaprolactone nanoplastics (PCL-NPs) using advanced in vitro intestinal models and the 3R-compliant in vivo Caenorhabditis elegans model. In vitro endpoints included cytotoxicity, oxidative stress, DNA damage, cellular internalization, and barrier integrity, while in vivo analyses focused on oxidative stress and locomotor behavior across multiple exposed generations. PS-NPs induced significant DNA damage in vitro, particularly at ≥50 µg/mL after 24–48 h exposure, and were rapidly internalized by cells, with 20 nm particles also detected in the nucleus. In contrast, 100 nm PCL-NPs elicited weaker biological responses. In vivo, PS-NPs caused an increase in oxidative stress response and locomotor behavior across exposed generations, whereas PCL-NPs produced milder effects, consistent with in vitro findings. These results support the potential of integrated NAMs for assessing human health risks associated with MNP exposure within a One Health framework.