Plastic contamination in freshwater ecosystems continues to rise, resulting in micro- and nanoparticle accumulation in the aquatic environment. A new study by an aquatic ecology group at the University of Eastern Finland investigated how these tiny plastic particles and their surface charge affect fish reproductive traits, indicating that negative effects may be pronounced under stressful conditions.

Doctoral Researcher Dilshan Dissanayaka and team members investigated the impact of positively and negatively charged polystyrene nanoparticles on the reproductive biology of European whitefish, Coregonus lavaretus. While exposure to variously charged nanoparticles had no significant effect on sperm motility, an interesting finding arose when examining early embryo mortality under two different incubation settings. No obvious toxicological effects of nanoparticles were observed in controlled laboratory conditions. However, in a stressful environment with variable oxygen and turbulence conditions, positively charged nanoparticles seemed to increase embryo mortality, indicating a critical role of surface charge in toxicity assessment.

The difference between positively and negatively charged particles can be explained by their electrostatic interactions with biological components. Positively charged particles interact more strongly with negatively charged cell membranes, possibly enhancing cellular uptake and toxicity. Conversely, negatively charged particles may experience repulsion from similarly charged surfaces, reducing harmful effects.

“This mechanism aligns with established knowledge, but further investigation is needed to confirm the specific molecular pathways involved,” the researchers note.

The study emphasises that the current ecotoxicological assessments typically undertaken in controlled laboratory environments may underestimate real-world scenarios. This study provides important preliminary evidence on the role of environmental conditions in nanoplastics ecotoxicity, but more research is needed to fully understand especially the role of charge-dependent toxicity and underlying mechanisms. This includes molecular-level investigations, extended experiments under varying environmental conditions and multi-stressor scenarios that better mimic natural ecosystems.