Scientists from the City University of Hong Kong have demonstrated that nanoplastics can enter zebrafish via two pathways—waterborne and dietary exposure—and then cross biological barriers to enter the circulatory system, accumulating in organs such as the blood, brain, gills, liver, intestines, gonads, and muscles. The findings, published in Environmental Chemistry and Ecotoxicology, highlight the gills and intestines as the most important absorption organs, while the intestines serve as the primary excretion organ.
Plastic waste breaks down into smaller fragments, with those measuring less than 1 micrometer defined as nanoplastics. Aquatic animals inadvertently ingest these particles suspended in water or consume contaminated food. Due to their ultra-small size, nanoplastics can cross biological barriers, transferring to different organs after ingestion. This accumulation can have harmful effects, potentially stunting growth and reproduction in fish.
Previous field studies found plastic fragments inside fish, mostly within the digestive system, with some evidence of plastics entering the circulatory system. The new study, led by Wen-Xiong Wang, exposed zebrafish to nanoplastics and tracked their movement. Within 24 hours of ingestion, nanoplastics entered the bloodstream and spread throughout the body, accumulating in critical tissues including the brain, gills, liver, intestine, gonads, and muscle. This widespread accumulation could potentially lead to disorders in the nervous and reproductive systems.
The researchers discovered that most nanoplastics entered through the gills and intestine and were primarily expelled through the intestine, though a portion remained trapped within the body for a long time. Based on these results, the team developed a computer model that simulates nanoplastic accumulation, travel, and clearance in fish organs, whether ingested from water or food. This model provides a valuable reference for predicting how nanoplastics might behave in mammals.
'Our study demonstrates that nanoplastics can cross biological barriers, enter the circulatory system of fish, and spread throughout their bodies,' said Wang. 'This alarming journey may also occur in other animals, and even in humans.' The study was supported by the National Science Foundation of China and the General Research Fund of Hong Kong Research Grants Council. The full study is available at https://doi.org/10.1016/j.enceco.2025.10.002.
