Global warming enhances nanoplastics toxicity: Insights into body shrinkage and energy deficit

Understanding the effects of global warming on nanoplastics ecotoxicity is crucial for environmental safety, yet the underlying mechanisms remain poorly understood. This study investigates the effects of low concentration polystyrene nanoplastics (PS-NPs) on Daphnia magna over three generations, under different mean temperature (MT) and daily temperature fluctuations (DTF), simulating both current and projected climate scenarios, and further explored the underlying mechanisms. Our results demonstrate that nanoplastics impaired growth, reproduction, and behavior, which were all exacerbated under elevated MT and/or DTF. Notably, Daphnia body size was significantly reduced in warming conditions, aligning with the temperature-size rule, which may further promote the microplastics intake due to the increased surface-to-volume ratio. Transcriptomic analysis revealed key mechanisms behind the size reduction, including disruption of chitin-based cuticle development, chitin binding, and cuticle structure components. Furthermore, nanoplastics also predominantly downregulate energetic metabolic pathways, with a more pronounced effect at elevated MT. Weighted Gene Co-expression Network Analysis (WGCNA) further confirmed the suppressed chitin and cuticle development and energy metabolism contribute to the enhanced nanoplastics toxicity under warming. This study highlights the amplified toxicity of nanoplastics in a warming world and provides proof-of-principle that body shrinkage and energy deficits are the key underlying mechanisms.