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 zebrafish, cross biological barriers, and accumulate in critical organs. The findings, published in Environmental Chemistry and Ecotoxicology, show these particles can translocate to the blood, brain, gills, liver, intestines, gonads, and muscles, potentially causing harmful effects such as stunted growth and reproduction. This research is important because it reveals a pathway for plastic pollution to impact biological systems at a cellular level, with implications for aquatic ecosystems and, due to physiological similarities, possibly human health.

Plastic waste degrades into smaller fragments in the environment, and aquatic animals like fish inadvertently ingest nanoplastics suspended in water or consume contaminated food. The study exposed zebrafish to nanoplastics and found that within 24 hours, particles 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 primary absorption organs, while the intestines also served as the main excretion route, though some particles remained trapped long-term. This widespread accumulation could lead to disorders in systems like the nervous and reproductive systems.

Previous field studies had found plastic fragments inside fish, mostly in the digestive system, with some evidence of particles in the circulatory system. The new research addresses how these particles enter the bloodstream and travel through the body. Using zebrafish—a common model in toxicology that shares many physiological and genetic similarities with humans—the team developed a computer model that simulates how nanoplastics accumulate, travel, and are cleared from different organs, whether ingested from water or food. This model provides a valuable reference for predicting nanoplastics behavior in mammals. The study's details are available in the journal article at https://doi.org/10.1016/j.enceco.2025.10.002.

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 highlights the potential for nanoplastics to disrupt ecosystems by affecting fish health and reproduction, which could ripple through food chains. For industries reliant on aquaculture or wild fisheries, this poses a risk to sustainability and food safety. Globally, it underscores the urgent need to address plastic pollution, as its microscopic remnants may have far-reaching biological impacts beyond visible waste. The study was supported by the National Science Foundation of China and the Hong Kong Research Grants Council.