In-depth comparative immunotoxicity assessment of pristine and aged PLA microplastics in zebrafish larvae: Bioaccumulation and NF-κB signaling insights

Polylactic acid (PLA) plastics are widely utilized as biodegradable alternatives, yet their fragmentation into microplastics (MPs) poses ecological risks. Comprehensive assessments and mechanistic insights into their immunotoxicity are currently lacking. This study systematically evaluated immunotoxic effects and underlying mechanism of pristine and aged PLA (APLA) MPs in larval zebrafish. UV treatment resulted in surface fragmentation, bond cleavage, reduced particle size, and increased oxygen-containing functional groups. Larval exposure (6-120 hpf) to PLA/APLA led to preferential intestinal accumulation, with APLA showing greater bioaccumulation than PLA. Under the influence of intestinal digestive enzymes, PLA/APLA MPs underwent degradation to varying extents. Additionally, PLA/APLA exposure intensified oxidative stress, evidenced by increased SOD activity and excessive accumulation of ROS, MDA, and NO. It also increased innate immune cells, suppressed T-cell differentiation, and inhibited humoral immunity, with stronger effects observed for APLA. Mechanistic studies revealed that PLA/APLA activated the NF-κB signaling pathway, as evidenced by stable binding of PLA to NF-κB1 and NF-κB2 in molecular docking analysis. This was further validated by reduced immunotoxic effects upon treatment with the NF-κB inhibitor QNZ. These findings provide critical scientific evidence to guide the forecasting and prevention for the environmental health risk of biodegradable plastic particles.