Bioaccumulation and Toxic Effects of Micro- and Nanoplastics in Zebrafish: A Critical Review

The United Nations Environment Programme has reported that over 460 million tons of plastic are produced globally each year, with half being disposable. Each year, approximately 8 million tons of this plastic waste end up in oceans, rivers, and lakes, resulting in a continuous rise in the release of micro- and nanoplastics (MNPs) into the aquatic environment. Importantly, microplastics have penetrated aquatic organisms, food chains, and even human organs, including the placenta of newborns. The depth and scope of their impact have become an environmental problem affecting the world. Recently, MNPs research has increasingly focused on understanding the bioaccumulation of these particles across diverse ecosystems and species, as well as their potential toxicological effects, due to their persistence in the environment, ease of ingestion by organisms, and ability to traverse biological barriers. Studies have demonstrated that MNPs can accumulate in aquatic organisms, such as fish and invertebrates, leading to potential bioaccumulation and biomagnification through the food web. For instance, MNPs have been found in various organs, including the digestive system, gills, and liver of aquatic species, posing risks to their health, reproduction, and behavior. Toxicologically, MNPs induce a range of adverse effects, starting with oxidative stress and inflammation, as evidenced by increased reactive oxygen species (ROS) and upregulated pro-inflammatory genes like IL-1β in embryos exposed to polystyrene NPs. These cellular disruptions progress to developmental delays, such as reduced hatching rates and larval growth, and extend to neurotoxic outcomes, including altered swimming behavior and inhibited neurotransmitter function. Furthermore, reproductive impairments in adults and surprising transgenerational effects—where unexposed offspring exhibit reduced fertility and altered gene expression—underscore the pervasive and potentially heritable impact of MNPs. These findings highlight the importance of further exploring the multidimensional impacts of MNPs bioaccumulation and toxic effects in vivo. MNPs have been widely detected in aquatic environments worldwide, and their potential threats to aquatic ecosystems and organisms are of significant concern. Zebrafish (Danio rerio) is a pivotal model organism in environmental toxicology, valued for its biological characteristics, genetic similarities to humans, and the capacity for full life cycle studies, which together provide crucial insights into the ecological risks associated with MNPs. MNPs can enter the zebrafish body at various developmental stages through both ingestion and respiration. Small-sized MNPs have the ability to cross the blood-–brain barrier and intestinal barrier, spreading throughout different organs such as the liver, heart and brain. Exposure to MNPs can lead to toxic effects through both physical and chemical processes, including growth and developmental toxicity, oxidative stress, neurotoxicity, cardiotoxicity, genotoxicity, and immunotoxicity. Despite studies revealing the toxic effects of MNPs across multiple organ systems, several research gaps and challenges remain. The ADME (absorption, distribution, metabolism, and excretion) process of MNPs in zebrafish has yet to be quantitatively and mechanistically elucidated. Additionally, the regulatory mechanisms of toxicity associated and ecological impacts and complex interactions within natural environments with long-term low-concentration remain unclear. Thus, it is crucial to strengthen environmental management and risk aassessment, establish stricter regulations to reduce plastic pollution, and develop effective monitoring and remediation technologies to address this global issue. Overall, this review provides a comprehensive analysis of the toxic effects and underlying mechanisms of MNPs in zebrafish, offering critical insights that inform future research into their ecological risks.