Poly(methyl methacrylate) micro- and nanoplastics induce early mitochondrial dysfunction and cellular perturbations in Drosophila melanogaster

Heterogeneous micro- and nanoplastic (MNPLs) mixtures, which consist of particles of varying sizes, shapes, and physical and chemical properties, represent the dominant form of environmental plastic pollution. To better understand the biological effects of environmentally relevant MNPLs, the effects of heterogeneous polymethyl methacrylate (PMMA) particles (approximately 100 nm – 80 μm) were investigated in Drosophila larvae. Physicochemical characterization confirmed a marked variation in particle size and shape. Transmission electron microscopy and confocal imaging revealed particle ingestion, intestinal uptake, intracellular localization, and translocation into the hemolymph. Although exposure to PMMA-MNPLs did not cause any apparent toxic effects, it mediates pronounced molecular and subcellular alterations. Gene expression analyses revealed selective modulation of cellular stress ( Hsp70 ), antioxidant defence ( Cat ), innate immunity ( PPO2, Imd, Duox ), detoxification, and tissue homeostasis pathways, indicating early adaptive responses as confirmed by the strong induction of Cyp4g1 involved in enhancing cuticular barrier formation and penetration resistance. At the highest PMMA-MNPLs concentration, gene expression levels were significantly increased for genes involved in tissue homeostasis, metabolism, and cellular maintenance, including Decay, Jon65Aii, and hll . The observed non-monotonic dose response patterns indicate the activation of compensatory mechanisms that temporarily maintain the organism's internal balance despite underlying cellular perturbations.