Nanoplastics and Neurodegeneration: A Roadmap From Mechanism to Causation.

Nanoplastics are ubiquitous by-products of global plastic production and have emerged as a potentially consequential yet insufficiently defined threat to health. Recent studies have revealed that these synthetic particulates can cross the blood-brain barrier, accelerate amyloid aggregation, impair microglial clearance, hijack the gut-liver-brain axis, and drive neuroinflammation-mechanisms central to neurodegeneration in Alzheimer's and Parkinson's disease. In addition, anionic nanoplastics can induce vascular endothelial leakiness, thereby harboring a paracellular route for their systemic and cerebral access. Yet causality remains unproven in implicating nanoplastics for neurodegeneration in the absence of standardized human exposure data, mechanistic specificity, and epidemiological evidence, especially considering the supra-environmental doses employed. Here, we synthesize current knowledge, examine barriers to causal understanding, and propose a roadmap to advance this emerging scientific frontier of great public concern and inform future strategies for sustainable materials innovation.