Scientists from the City University of Hong Kong have discovered that nanoplastics can enter zebrafish through two pathways—waterborne and dietary exposure—and then translocate to multiple organs, including the brain, gills, liver, intestines, gonads, and muscles. The findings, published in Environmental Chemistry and Ecotoxicology, highlight the ability of these ultra-small particles to cross biological barriers and enter the circulatory system, with potential implications for human health.
Plastic waste breaks down into fragments smaller than 1 micrometer, known as nanoplastics. Aquatic animals inadvertently ingest these particles from water or contaminated food. Due to their tiny size, nanoplastics can cross biological barriers and spread throughout the body. Previous field studies found plastic fragments in fish, mostly in the digestive system, with some evidence of particles in the heart. This study aimed to understand how nanoplastics enter the bloodstream and travel through the body.
Using zebrafish, a common model in toxicology research due to physiological and genetic similarities to humans, the researchers exposed the fish to nanoplastics. Within 24 hours of ingestion, the particles entered the bloodstream and accumulated in organs, reaching stable levels within days. The most important absorption organs were the gills and intestines, while the intestines served as the primary excretion organ. However, a portion of nanoplastics remained trapped in the body long-term.
Based on these results, the team developed a computer model simulating nanoplastic behavior in fish. The model successfully predicted accumulation, travel, and clearance from different organs after ingestion via water or food. This model provides a valuable reference for predicting nanoplastic behavior in mammals, according to the researchers.
"Our study demonstrates that nanoplastics can cross biological barriers, enter the circulatory system of fish, and spread throughout their bodies," said corresponding author Wen-Xiong Wang. "This alarming journey may also occur in other animals, and even in humans." The widespread accumulation could potentially lead to disorders in the nervous and reproductive systems.
The study was supported by the National Science Foundation of China and the Hong Kong Research Grants Council. For more details, the full paper is accessible at https://doi.org/10.1016/j.enceco.2025.10.002.
