Nanoplastics Cross Biological Barriers and Accumulate in Zebrafish Organs, Study Finds

Scientists from the City University of Hong Kong have discovered that nanoplastics can enter zebrafish through two pathways: waterborne exposure and dietary exposure. These tiny particles, defined as plastic fragments measuring less than 1 micrometer, can cross biological barriers to enter the circulatory system and then translocate to and accumulate in various organs, including the blood, brain, gills, liver, intestines, gonads, and muscles. The study, published in Environmental Chemistry and Ecotoxicology, found that within 24 hours of ingestion, nanoplastics entered the bloodstream and spread throughout the body, quickly accumulating in organs and reaching a stable level within days.

The researchers identified the gills and intestines as the most important absorption organs, while the intestines serve as the primary excretion organ. However, a portion of nanoplastics remained trapped within the body for extended periods. This widespread accumulation could potentially lead to disorders in systems like the nervous and reproductive systems, with the most severe cases potentially stunting growth and reproduction in fish. Previous field studies had found plastic fragments inside fish, mostly within the digestive system, with evidence of plastics entering the circulatory system, such as fragments found in the heart.

Zebrafish are commonly used in toxicology research due to their physiological and genetic similarities with humans. The researchers exposed zebrafish to nanoplastics and found particles ingested via water or food in critical tissues, including the brain, gills, liver, intestine, gonads, and muscle. Based on these experimental results, the research team developed a computer model that simulates nanoplastics in fish's bodies. This model successfully predicted how nanoplastics accumulate, travel, and are cleared from different organs, whether ingested from water or food, and provides a valuable reference for predicting how nanoplastics might behave in mammals.

Corresponding author Wen-Xiong Wang stated, "Our study demonstrates that nanoplastics can cross biological barriers, enter the circulatory system of fish, and spread throughout their bodies. This alarming journey may also occur in other animals, and even in humans." The research was supported by the National Science Foundation of China and the Hong Kong Research Grants Council. The full study is available at https://doi.org/10.1016/j.enceco.2025.10.002.