Nanoplastics Drive the Charge-specific Decline of Aquatic Insect (<i>Chironomus kiinensis</i>) Emergence through Inducing Oxidative Damage and Perturbing the Endocrine System

The ongoing decline in the emergence and biomass of aquatic insects is partly due to the wide distribution of engineered nanoparticles. Nanoplastics (NPs), as emerging engineered nanoparticles, can cause toxicity to aquatic organisms. However, the mechanisms underlying the effects of NPs on aquatic insect emergence are not clear. Here, we explored the accumulation of NPs, phenotypic alterations, and physiological and transcriptional responses of <i>Chironomus kiinensis</i> to NPs carrying positive (NP+) and negative (NP-) charges under environmentally relevant concentrations. Results revealed that NP+ induced more reduction of the emergence rate (85.6% for 1 g/kg NP- group and 77.8% for 1 g/kg NP+ group) and the increase of emergence time of <i>C. kiinensis</i> than NP-. This occurred because NP+ were more easily accumulated in larvae than NP- for their stronger electrostatic interactions with negatively charged biomembranes and less agglomeration in exposure media. Compared with NP-, NP+ led to greater oxidative damage through perturbation of the gene expression related to oxidative stress in <i>C. kiinensis</i>. Moreover, the expression of genes associated with emergence was more disrupted in organisms exposed to NP+ than that exposed to NP-, thereby influencing the hormone contents and emergence process of insect. These findings provided new insights into the molecular mechanism that charged NPs affect aquatic insect emergence.