**7. Conclusions**

Exposure to nanoparticles of natural and anthropogenic origin is practically inevitable, either because they are present in environmental pollution or because they are used as components in many products for biomedical, cosmetic, structural, or other applications. Their small size and composition give them unique physicochemical features that influence the way how they interact with the organism; some of these nanoparticles can pass easily through membranes intended to protect our cells, others cannot be excreted and will bioaccumulate in tissues and organs with all the consequences that may derive not only from their localization, but also from their reactivity, aggregation, or even their potential to modify gene expression patterns. Therefore, their translocation to the brain continues to be studied both to identify entry routes of toxic agents as well as to exploit these mechanisms for drug delivery, internalization of contrast media, and in various other applications.

From these data, it is important to know whether different nanomaterials present in environmental pollution manage to translocate to the brain when they are aerosolized, how they are biodistributed, whether they have effects associated with neurodegeneration, etc. This would make it possible to issue recommendations on the strategies required to deal with environmental pollution, but also to regulate the fate of nanomaterials from different industries and to implement protocols for their manufacture, manipulation, and disposal. This may also have an impact on the identification of better drug delivery vehicles to the brain, which has been extremely complex due to the limitations on mobility that the BBB represents to the passage of drugs entering the organism through the different routes of administration.

For that matter, it is important to find an answer to whether there is a neurodegenerative effect derived from chronic exposure to aerosolized silica, magnetite, or carbon black nanoparticles in animal models, to deepen in our understanding of neurodegeneration processes and identify potential entry routes of nanoparticles into the brain. Approaches through *in vivo* models can lead the way for clinical studies with a broader result of possible nanoparticle damaging effects. However, knowing that inhaled nanopollutants can translocate to the brain and promote neurodegenerative effects has implications in the way we approach disease, but also in prevention and, in the public policies created to regulate exposition to nanomaterials independently of their source. Since prevention is the best health approach possible, it is where our

efforts should be concentrated. It can save lives, suffering, and money to a greater extent than solutions brought once a health problem has exploded. For that matter, studying the effects of nanopollutants present in the air that we are breathing every day at higher rates, is a fundamental step to gather the necessary information needed to create preventive strategies concerning pollution exposition to prevent health risks.
