Tissue-specific Responses of Duckweed to Cadmium Stress under Nanoplastic Co-exposure: Differential Accumulation and Toxicity in Roots and Fronds

Nanoplastics (NPs), characterized by their small size and widespread presence, are known to interact with other contaminants, potentially modifying their environmental behavior and biological impacts. Herein, we explored the response of duckweed (Spirodela polyrhiza) to Cd (0, 0.01, 0.1, 1 mg/L) stress upon co-exposure to polystyrene NPs (PS-NPs) (0, 0.1, 1, 10 mg/L). Cd exhibits significantly higher toxicity to the duckweed compared to PS-NPs. Notably, the presence of PS-NPs exacerbates Cd toxicity in the roots, while mitigating its adverse effects on the fronds. In-situ analyses using Laser Ablation Inductively Coupled Plasma Mass Spectrometry and Confocal Laser Scanning Microscopy demonstrate that PS-NPs enhance Cd accumulation in the root tips (by up to 19.3%) but reduce its presence in the basal root regions and further translocation to the fronds by up to 26.8%. Metabolomics and gene expression analyses further indicate that PS-NPs elevate organic acid contents and modify gene expressions in duckweed against exogenous Cd stress, thereby inhibiting the root-to-frond translocation of Cd. The findings enhance our comprehension of the complex interactions between NPs and environmental pollutants in aquatic flora.