Single and combined effects of polystyrene nanoplastics and Cd on submerged plants Ceratophyllum demersum L.

Nanoplastics (NPs) and heavy metals are widely distributed in aquatic ecosystem, posing a potential threat to ecosystem function. Submerged macrophytes play an important role in water purification and maintaining ecological functions. However, the coupled effects of NPs and cadmium (Cd) on submerged macrophytes physiology and the mechanisms involved are still unclear. Here, the potential effects of single and co-Cd/PSNPs exposure on Ceratophyllum demersum L. (C. demersum) were explored. Our results showed that NPs aggravated the inhibition of Cd on plant growth ate (a decrease of 35.54 %), reduced chlorophyll synthesis (a decrease of 15.84 %), and disrupted the antioxidant enzyme system (a decrease of 25.07 % on SOD activity) of C. demersum. Massive PSNPs adhered to the surface of C. demersum when exposed to co-Cd/PSNPs while they did not adhere when exposed to single-NPs. The metabolic analysis further demonstrated that co-exposure down-regulated plant cuticle synthesis and that Cd exacerbated the physical damage and shadowing effects of NPs. In addition, co-exposure upregulated pentose phosphate metabolism, leading to the accumulation of starch grains. Furthermore, PSNPs reduced Cd enrichment capacity of C. demersum. Our results unraveled distinct regulatory networks for submerged macrophytes exposed to single and composite of Cd and PSNPs, providing a new theoretical basis for assessing the risks of heavy metals and NPs in the freshwater environment.