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Extract from the European Union Public health committee report on Nanoparticles  [Source document: SCENIHR (2006); Summary & Details: GreenFacts (2007]

Nanoparticles, can have the same dimensions as biological molecules such as proteins.

..... the interaction with living systems is also affected by the dimensions of the nanoparticles. For instance, nanoparticles no bigger than a few nanometres may reach well inside biomolecules, which is not possible for larger nanoparticles. Nanoparticles may cross cell membranes. It has been reported that inhaled nanoparticles can reach the blood and may reach other target sites such as the liver, heart or blood cells.

Key factors in the interaction with living structures include nanoparticle dose, the ability of nanoparticles to spread within the body, as well as their solubility. Some nanoparticles dissolve easily and their effects on living organisms are the same as the effects of the chemical they are made of. However, other nanoparticles do not degrade or dissolve readily. Instead, they may accumulate in biological systems and persist for a long time, which makes such nanoparticles of particular concern.

There remain many unknown details about the interaction of nanoparticles and biological systems and more information on the response of living organisms to the presence of nanoparticles of varying size, shape, chemical composition and surface characteristics is needed to understand and categorize the toxicity of nanoparticles

…..Inhaled particulate matter can be deposited throughout the human respiratory tract, and an important fraction of inhaled nanoparticles deposit in the lungs. Nanoparticles can potentially move from the lungs to other organs such as the brain, the liver, the spleen and possibly the foetus in pregnant women.

Data on these pathways is extremely limited but the actual number of particles that move from one organ to another can be considerable, depending on exposure time. Even within the nanoscale, size is important and small nanoparticles have been shown to be more able to reach secondary organs than larger ones.

Another potential route of inhaled nanoparticles within the body is the olfactory nerve; nanoparticles may cross the mucous membrane inside the nose and then reach the brain through the olfactory nerve.

Materials which by themselves are not very harmful could be toxic if they are inhaled in the form of nanoparticles.

The effects of inhaled nanoparticles in the body may include lung inflammation and heart problems. Studies in humans show that breathing in diesel soot causes a general inflammatory response and alters the system that regulates the involuntary functions in the cardiovascular system, such as control of heart rate.

The pulmonary injury and inflammation resulting from the inhalation of nanosize urban particulate matter appears to be due to the oxidative stress that these particles cause in the cells

 ….........The use of nanoparticles as drug carriers may reduce the toxicity of the incorporated drug but it is sometimes difficult to distinguish the toxicity of the drug from that of the nanoparticle. Toxicity of gold nanoparticles, for instance, has been shown at high concentrations. In addition, nanoparticles trapped in the liver can affect the function of this organ.

Nanoparticles have the potential to cross the blood brain barrier, which makes them extremely useful as a way to deliver drugs directly to the brain. On the other hand, this is also a major drawback because nanoparticles used to carry drugs may be toxic to the brain.