Chronic toxicity effects of sediment-associated polystyrene nanoplastics alone and in combination with cadmium on a keystone benthic species Bellamya aeruginosa

Nanoplastics (NPs) are emerging pollutants that may adversely affect aquatic fauna. However, the adverse effects of NPs and heavy metals, both alone and combined on freshwater benthic fauna remain largely unclear. Here, we performed a 28-day sediment toxicity test with Bellamya aeruginosa to examine the effects of exposure to polystyrene nanoplastics (PSNPs) and co-exposure to PSNPs and Cd. Cd bioavailability, the bioaccumulation of PSNPs and Cd, and changes in multiple biomarkers were determined. The results revealed that PSNPs significantly increased Cd bioavailability and thereby facilitated Cd bioaccumulation; however, PSNPs displayed a negligible vector role in Cd uptake by B. aeruginosa. The results demonstrated that PSNPs can accumulate in B. aeruginosa and induce oxidative damage and DNA damage. Co-exposure to PSNPs and Cd significantly enhanced oxidative damage and DNA damage and reduced metallothionein levels. The integrated biomarker response index analysis showed that co-exposure to PSNPs and Cd considerably increased toxic stress in B. aeruginosa compared to single PSNPs or Cd exposure, suggesting that PSNPs may have a synergistic effect with Cd. Collectively, our findings highlight that PSNPs not only cause toxicity to B. aeruginosa but also significantly enhance the toxicity of Cd by increasing Cd bioavailability in the sediment.