Differential immunotoxic effects of UV-aged polypropylene and polyamide microplastics in Ruditapes philippinarum hemocytes: An extracellular trap perspective

Microplastics (MPs) in marine environments undergo ubiquitous UV aging, which can substantially alter their physicochemical properties and biological toxicity. However, whether UV aging increases the toxicological risk of different polymer MPs and how cellular immune responses reflect this process remain unclear. In this study, hemocytes of the Manila clam ( Ruditapes philippinarum ) were used as an in vitro model to investigate the immunotoxic effects of pristine and UV-aged polypropylene (PP) and polyamide (PA) MPs at the cellular level. The results showed that UV aging markedly aggravated PP-induced immunotoxicity, as evidenced by reduced hemocyte viability, increased reactive oxygen species production, enhanced myeloperoxidase activity, and elevated extracellular trap-related responses. In contrast, UV aging had limited effects on PA-induced toxicity. Proteomic analysis of ET-enriched extracellular fractions revealed that UV-aged PP activated multiple immune and inflammatory pathways, including NF-κB signaling, whereas UV-aged PA mainly induced broader proteomic remodeling related to signal transduction, protein synthesis, and cellular homeostasis. Notably, the PA-UV group yielded more differentially expressed proteins than the PP-UV group but exhibited weaker functional immunotoxicity, indicating that biological outcomes depend more on the functional enrichment of altered proteins than on the total number of differentially expressed proteins. Under the present exposure conditions, PP behaved as an aging-sensitive polymer, whereas PA showed relatively aging-tolerant toxicological responses. These findings deepen the mechanistic understanding of polymer-specific MPs toxicity under UV aging and highlight the need to incorporate polymer identity into the ecological risk assessment of aged MPs.