Nanoplastics potentiate mercury toxicity in a marine copepod under multigenerational exposure

The continuous fragmentation of plastics and release of synthetic nanoplastics from products have been aggra-vating nanoplastic pollution in the marine ecosystem. The carrier role of nanoplastics may increase the bioavailability and toxicity effects of toxic metals, e.g., mercury (Hg), which is of growing concern. Here, the copepod Tigriopus japonicus was exposed to polystyrene nanoplastics (PS NPs) and Hg (alone or combined) at environmental realistic concentrations for three generations (F0-F2). Then, Hg accumulation, physiological endpoints, and transcriptome were analyzed. The results showed that the copepod's reproduction was signifi-cantly inhibited under PS NPs or Hg exposure. The presence of PS NPs caused significantly higher Hg accu-mulation, lower survival, and lower offspring production in copepods relative to Hg exposure, suggesting an increased threat to the copepod's survivorship and health. From the molecular perspective, combined PS NPs and Hg caused a graver effect on the DNA replication, cell cycle, and reproduction pathways relative to Hg exposure, linking to lower levels of survivorship and reproduction. Taken together, this study provides an early warning of nanoplastic pollution for the marine ecosystem not only because of their adverse effect per se but also their carrier role for increasing Hg bioaccumulation and toxicity in copepods.

Automated summary

This study reveals that the combined exposure of polystyrene nanoplastics (PS NPs) and mercury (Hg) poses a greater threat to the survival and health of the copepod Tigriopus japonicus. Not only do PS NPs and Hg have adverse effects on their own, but PS NPs also enhance Hg bioaccumulation and toxicity in copepods. This study provides an early warning of nanoplastic pollution in the marine ecosystem.