Overall effects of microplastics on brain.

Microplastic (MP) and nanoplastic (NP) pollution represents a pervasive environmental issue, raising significant concerns regarding potential neurotoxicity and impacts on brain health. This review synthesizes recent research findings to provide a comprehensive overview of the effects of MPs/NPs on the brain. Evidence demonstrates that MPs/NPs can cross critical biological barriers, including the blood-brain barrier and the placenta, gaining access to the central nervous system (CNS) and the developing fetal brain, influenced by particle size, charge, and the biomolecular corona. Once present, MPs/NPs trigger multiple detrimental pathways, including oxidative stress, persistent neuroinflammation involving microglia and astrocytes, mitochondrial dysfunction leading to energy deficits, disruption of crucial neurotransmitter systems, and direct neuronal damage. Critically, NPs have been shown to promote the aggregation of proteins implicated in neurodegeneration, such as alpha-synuclein. These mechanistic disturbances translate into observable adverse outcomes in experimental models, ranging from cognitive impairments in learning and memory to behavioral abnormalities and pathologies resembling human neurodegenerative and neurodevelopmental disorders. Toxicity is modulated by particle characteristics, co-exposures, and host factors like age and sex, with indirect effects via the gut-brain axis also playing a significant role. While current evidence, primarily from animal models often using high doses, strongly indicates a neurotoxic potential, significant research gaps remain concerning human risk assessment under chronic, low-level environmental exposure conditions and the effects of environmentally aged, mixed-plastic particles. Future research should prioritize human studies, environmentally realistic exposure scenarios, and differentiating direct versus indirect neurotoxic mechanisms to accurately evaluate the threat MPs/NPs pose to human brain health.