Study Reveals How Nanoplastics Travel Through Zebrafish Bodies, Raising Concerns for Aquatic Life and Human Health

Scientists from City University of Hong Kong have discovered that nanoplastics can enter zebrafish through two distinct pathways: waterborne exposure and dietary exposure. These minuscule plastic particles, measuring less than 1 micrometer, can cross biological barriers to enter the circulatory system and subsequently translocate to and accumulate in various organs. The research, published in Environmental Chemistry and Ecotoxicology, found nanoplastics in the blood, brain, gills, liver, intestines, gonads, and muscles of exposed zebrafish.

Within 24 hours of ingestion, nanoplastics entered the bloodstream and spread throughout the body, quickly accumulating in organs and reaching stable levels within days. The gills and intestines were identified as the most important absorption organs, while the intestines served as the primary excretion organ. However, a portion of nanoplastics remained trapped within the body for extended periods, leading to persistent accumulation in critical tissues.

This widespread accumulation could potentially lead to disorders in systems like the nervous and reproductive systems, with the most severe cases potentially stunting fish growth and reproduction. Previous field studies have found plastic fragments inside fish, mostly within the digestive system, with evidence of plastics entering the circulatory system. The new research provides insight into how these particles enter the bloodstream and travel through the body.

Based on experimental results, the researchers developed a computer model that simulates nanoplastics in fish bodies. This model successfully predicted how nanoplastics accumulate, travel, and are cleared from different organs, whether ingested from water or food. The model also provides a valuable reference for predicting how nanoplastics might behave in mammals, including humans.

"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 research findings are detailed in the study available at https://doi.org/10.1016/j.enceco.2025.10.002.

Zebrafish are commonly used in toxicology research due to their physiological and genetic similarities with humans, making these findings particularly relevant for understanding potential human health impacts. As plastic waste breaks down into smaller fragments in the environment, aquatic animals inadvertently ingest nanoplastics suspended in water or consume contaminated food. The ability of these ultra-small particles to cross biological barriers represents a significant environmental and health concern.

The study was supported by the National Science Foundation of China and the General Research Fund of Hong Kong Research Grants Council. Wang was supported by a 5-year Senior Research Fellowship from the Hong Kong Research Grants Council. These findings contribute to growing understanding of microplastic pollution's biological impacts and highlight the need for further research into nanoplastics' effects on ecosystems and human health.