Micro(Nano)plastics triggered size- and burden-dependent gut heterogeneous acidification and oxidative stress in a marine copepod.

Globally, an overwhelming amount of micro(nano)plastic (MNP) is accumulated in ocean due to poor waste management. This study combined fluorescence imaging and toxicological modeling to evaluate the gut acidification and oxidative stress in a marine copepod Parvocalanus crassirostris induced by MNPs at varying concentrations and food conditions. Using aggregation-induced emission luminogens (AIEgens)-labeled MNPs and probes, we visualized and quantified pH and reactive oxygen species (ROS) in copepods to reveal the size- and burden-dependent spatial heterogeneous effects triggered by 5 μm MP and 200 nm NPs. MPs and NPs caused anterior midgut acidification (+21.6 % and +16.6 %, respectively), while reduced posterior gut acidity. Diatoms exacerbated the MNP -induced acidification (+59.6 %) but alleviated ROS overproduction. Despite limited internalization, MNP triggered systemic ROS elevation, with NPs inducing stronger stress (+58.8 % vs. MPs +10.4 %). A log-logistic toxicological model established a relationship between the in vivo MNP burden and ROS, with MPs eliciting steeper curves and lower oxidative stress induction thresholds, but lower maximum ROS production than NPs. The diatoms supply elevated oxidative stress level. This study highlighted the heterogeneity effects of MNPs, providing insights into the sublethal impacts on marine zooplankton.