Nanoplastics Cross Biological Barriers in Zebrafish, Raising Concerns for Aquatic Life and Human Health

Scientists from the City University of Hong Kong have documented how nanoplastics—plastic particles smaller than 1 micrometer—enter, travel through, and accumulate in the bodies of zebrafish. The research, published in Environmental Chemistry and Ecotoxicology, shows these particles can cross biological barriers, enter the circulatory system, and translocate to multiple organs after just 24 hours of exposure.

The study found zebrafish absorbed nanoplastics through two primary pathways: direct uptake from water through the gills and dietary exposure through contaminated food. Once ingested, the particles rapidly entered the bloodstream and spread throughout the body, accumulating in critical tissues including the blood, brain, gills, liver, intestines, gonads, and muscles. The gills and intestines served as the most important absorption organs, while the intestines were the primary route of excretion, though a portion of nanoplastics remained trapped in the body long-term.

This widespread accumulation is significant because it could lead to harmful effects on the organism, with severe cases potentially stunting growth and reproduction. The presence of nanoplastics in organs like the brain and gonads suggests potential risks to nervous and reproductive systems. The findings address a key question in environmental toxicology: how plastic fragments found in field studies enter the bloodstream and travel through the body, beyond just the digestive system.

Using these experimental results, the researchers developed a computer model that simulates how nanoplastics accumulate, travel, and are cleared from different organs in fish, whether ingested from water or food. This model, detailed in the study available at https://doi.org/10.1016/j.enceco.2025.10.002, also provides a valuable reference for predicting how nanoplastics might behave in mammals, including humans.

The implications of this research extend beyond zebrafish, which are commonly used in toxicology due to their physiological and genetic similarities with humans. Corresponding author Wen-Xiong Wang noted that the alarming journey of nanoplastics in fish may also occur in other animals and potentially in humans, highlighting a broader environmental and public health concern. As plastic waste breaks down into smaller fragments in aquatic environments, organisms inadvertently ingest these particles, leading to bioaccumulation that could disrupt ecosystems and food chains.

This study underscores the pervasive nature of plastic pollution and its capacity to infiltrate living organisms at a microscopic level. The ability of nanoplastics to cross biological barriers and accumulate in vital organs raises urgent questions about long-term impacts on wildlife health and the potential for trophic transfer to humans through contaminated seafood. The research was supported by the National Science Foundation of China and the Hong Kong Research Grants Council, emphasizing its scientific priority in understanding emerging contaminants.