Effects of Microplastics and Nanoplastics on Neurodevelopment and Neurodegeneration in Zebrafish

Microplastic pollution has drawn the attention of scientists and the public in the last decade. The term “microplastic” was first used by Thompson to describe tiny plastic particles in the oceans. Classified based on their sizes, those with diameters ranging from 100 nanometers to 5 millimeters are termed “microplastics (MP),” while those with diameters between 1 and 100 nanometers are referred to as “nanoplastics (NP).” Due to their small sizes, microplastics and nanoplastics (MNPs) cannot be effectively removed from wastewater, leading them to easily mix into freshwater and the sea, causing harm to the environment and aquatic organisms. It has been demonstrated in various model organisms that these particles can accumulate in different regions of the body, crossing biological barriers such as the blood–brain barrier, and induce negative effects such as oxidative stress, cytotoxicity, neurotoxicity, energy loss, apoptosis, and inflammation. Even in humans, the presence of MP has been detected in various body components such as the placenta, feces, lung tissue, and blood. Zebrafish, commonly used as a model organism to study various organ systems and biological pathways, offer advantages such as rapid embryonic development, transparent structure, and genetic similarities with humans. Studies on zebrafish exposed to MNPs at different sizes and concentrations have shown that particles can pass through the chorion and enter the embryo, even at very low concentrations, reaching various organs in the body. Results of exposure include disruption of neurotransmitter metabolism, decreased locomotor activity, induced oxidative stress, and apoptosis. Functional and transcriptional analyses have indicated that neuronal development is significantly affected by the presence of MP, although the exact mechanism is not yet fully understood.