Q.What are the possible harmful effects of usage of Nanoparticles? Why?

The same properties that make nanoparticles useful also make them a genuine health concern, and research into this side of nanotechnology is treated as being just as important and just as active as research into applications. The central issue is dimensional: nanoparticles happen to be the same size as biological molecules such as proteins, so they can readily adsorb onto the surface of living organisms and from there enter the body's tissues and fluids. Whether a given nanoparticle adsorbs strongly or weakly depends on its surface characteristics -- a property that can be turned to advantage, since designing a nanoparticle's surface to adsorb specifically onto one target cell is exactly the mechanism that makes targeted drug delivery to a specific site in the body possible. But the same size-dependence cuts the other way too: particles only a few nanometres across can penetrate well inside biomolecules in a way that larger nanoparticles simply cannot, and they can cross cell membranes with relative ease. Inhaled nanoparticles are known to reach the bloodstream and, from there, other organs such as the liver, heart, or blood cells generally. Because so many of these variables -- size, shape, chemical composition, surface characteristics -- affect how a living organism responds, none of them can simply be assumed safe just because the particle in question is nano-sized, which is why this remains an active research question rather than a settled one. A companion diagram (marked 'not for examination', since it goes beyond what is formally assessed) maps specific exposure routes to specific disease associations: ingestion through the gastro-intestinal system is linked to Crohn's disease and colon cancer; orthopedic-implant wear debris is linked to auto-immune diseases, dermatitis, urticaria and vasculitis; inhalation reaching the lungs and circulatory system is linked to asthma, bronchitis, emphysema and cancer, and via the heart to arrhythmia, heart disease and death; nanoparticles reaching the brain are linked to Parkinson's disease and Alzheimer's disease; and further links are drawn to diseases of unknown cause in the kidneys and liver, and to the lymphatic system (podoconiosis, Kaposi's sarcoma).