Scientists from the City University of Hong Kong have demonstrated that nanoplastics can enter zebrafish through two pathways—waterborne and dietary exposure—and then cross biological barriers to reach the circulatory system and accumulate in various organs, including the blood, brain, gills, liver, intestines, gonads, and muscles. The study, published in Environmental Chemistry and Ecotoxicology, highlights that the gills and intestines are the most important absorption organs, while the intestines serve as the primary excretion organ. However, some nanoplastics remain trapped in the body for extended periods.
Plastic waste breaks down into smaller fragments in the environment, with those measuring less than 1 micrometer defined as nanoplastics. Aquatic animals such as fish inadvertently ingest these particles suspended in water or consume contaminated food. Because of their ultra-small size, nanoplastics can cross biological barriers and transfer to different organs after ingestion. This buildup can have harmful effects, potentially stunting growth and reproduction. Previous field studies found plastic fragments inside fish, mostly within the digestive system, and some evidence of plastics entering the circulatory system, such as fragments found in the heart. The new study sheds light on how these particles enter the bloodstream and travel through the body.
Zebrafish, commonly used in toxicology research due to their physiological and genetic similarities to humans, were exposed to nanoplastics. Within 24 hours of ingestion, the particles entered the bloodstream and spread throughout the body, quickly accumulating in organs and reaching stable levels within days. The particles were found in critical tissues, including the brain, gills, liver, intestine, gonads, and muscle. This widespread accumulation could potentially lead to disorders in systems like the nervous and reproductive systems. The researchers also discovered that most nanoplastics entered through the gills and intestine, and were primarily expelled through the intestine, though a portion remained trapped.
Based on these experimental results, the duo developed a computer model that simulates the nanoplastics in fish's body. 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. "Our study demonstrates that nanoplastics can cross biological barriers, enter the circulatory system of fish, and spread throughout their bodies," says corresponding author Wen-Xiong 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 Hong Kong Research Grants Council, as detailed in the related link.
