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NANOPARTICLES. WHAT ARE NANOPARTICLES? AN OVERVIEWPUBLIC HEALTH
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What are the physical and chemical properties of nanoparticles?
Nanoparticles often have unique physical and chemical properties. For example, the electronic, optical, and chemical properties of nanoparticles may be very different from those of each component in the bulk. At the nanoscale, materials behave very differently compared to larger scales and it is still very difficult to predict the physical and chemical properties of particles of such a very small size. The principal parameters of nanoparticles are their shape, size, surface characteristics and inner structure. Nanoparticles can be encountered as aerosols (solids or liquids in air), suspensions (solids in liquids) or as emulsions (liquids in liquids). In the presence of certain chemicals, properties of nanoparticles may be modified. The composition of a specific nanoparticle can be very complex, depending on what interactions it has had with other chemicals or particles and on its lifetime. The chemical processes taking place on the surfaces of nanoparticles are also very complicated and remain largely unknown.
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Nanoparticles have different ways of interacting with each other. They can remain free or group together depending on the attractive or repulsive interaction forces between them. These interactions remain difficult to characterize. Nanoparticles suspended in gas tend to stick to each other more readily than in liquids. Nanoparticles can group together
Credit: NanoPrism Technologies, Inc.
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How are nanoparticles formed?
Free nanoparticles may occur naturally, be released unintentionally by industrial or domestic processes such as cooking, manufacturing, and transport, or be specifically engineered for consumer products and advanced technologies. 4.1 In the liquid phase, engineered nanoparticles are mainly produced through controlled chemical reactions, while naturally occurring nanoparticles are generated by the erosion and chemical degradation of plants, clay, etc. |
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4.2 In the gas phase, both naturally occurring and engineered nanoparticles are generally created by chemical reactions whereby gases are converted into tiny liquid droplets which then condensate and grow. They rarely originate from the breaking down of larger particles. 4.3 Both in rural and urban areas, a litre of air can contain millions of nanoparticles. In urban areas, most nanoparticles come from diesel engines or cars with defective or cold catalytic converters. In some workplaces, exposure to airborne nanoparticles may represent a potential health risk.
What are the uses of nanoparticles in consumer products?
Nanoparticles can contribute to stronger, lighter, cleaner and “smarter” surfaces and systems. They are already being used in the manufacture of scratchproof eyeglasses, crack-resistant paints, anti-graffiti coatings for walls, transparent sunscreens, stain-repellent fabrics, self-cleaning windows and ceramic coatings for solar cells. Nanotechnology can be used to increase the safety of cars. Nanoparticles can improve adhesion of tyres to the road, reducing the stopping distance in wet conditions. In addition, the stiffness of the car body can also be improved by use of nanoparticle-strengthened steels. Moreover, ultra-thin transparent coatings can be applied to displays or panes to avoid glare or condensation, and in the future it may be possible to produce transparent car body parts to improve all-round vision.
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Nanotechnology can be applied in the processing of food. In addition, food packaging – and, as a result, food safety – can be improved through nanomaterials placing anti-microbial agents on coated films and modifying gas permeability as required for different products. |
Nanomaterials are also being used in biology and medicine in a wide variety of ways. Examples include products for drug delivery and gene therapy, tissue engineering, DNA probes and nanoscale “biochips”.
What are potential harmful effects of nanoparticles? |
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6.1 Nanoparticles can have the same dimensions as some biological molecules and can interact with these. In humans and in other living organisms, they may move inside the body, reach the blood and organs such as the liver or the heart, and may also cross cell membranes. Insoluble nanoparticles are a greater health concern because they can persist in the body for long periods of time.
6.2 The parameters of nanoparticles that are relevant for health effects are nanoparticle size (smaller particles can be more dangerous), chemical composition and surface characteristics, and shape.
Materials which by themselves are not very harmful could be toxic if they are inhaled in the form of nanoparticles. |
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6.3 Inhaled nanoparticles can deposit in the lungs and then potentially move to other organs such as the brain, the liver, and the spleen, and possibly the foetus in pregnant women. Some materials could become toxic if they are inhaled in the form of nanoparticles. Inhaled nanoparticles may cause lung inflammation and heart problems.
6.4 The objective of nanoparticles used as drug carriers is to deliver more of the drug to the target cells, to reduce the harmful effects of the drug itself on other organs, or both. However, it is sometimes difficult to distinguish the toxicity of the drug from that of the nanoparticle.
6.5 With the exception of airborne particles reaching the lungs, information on the behaviour of nanoparticles in the body is still minimal. Assessment of the health implications of nanoparticles should take into account the fact that age, respiratory tract problems, and the presence of other pollutants can modify some of the health effects.
6.6 Information on the effects of nanoparticles on the environment is very scarce. However, it is likely that many conclusions drawn from human studies can be extrapolated to other species, but more research is needed.
How can inhaled nanoparticles affect health?
Particulate matter present in air pollution, especially from traffic emissions, is known to affect human health, although it is not clear exactly how. Epidemiological studies on ambient air pollution have not proved conclusively that nanoparticles are more harmful than larger particles, but these studies may not be well suited to demonstrate such differences. |
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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. Out of three human studies, only one showed a passage of inhaled nanoparticles into the bloodstream. Materials which by themselves are not very harmful could be toxic if they are inhaled in the form of nanoparticles. |
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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.
How can exposure to nanoparticles be measured?
7.1 Detecting nanoparticles is difficult, both in gases and in liquids. Nanoparticles are so small that they can only be detected by electron microscopes. Instruments able to detect and analyse particles of a few nanometres were only developed recently.
7.2 Most people are routinely exposed to nanoparticles in ambient air, primarily from diesel fumes. Exposure to airborne nanoparticles is low in terms of mass but significant in terms of numbers of particles. It is the number of particles, their size, and their surface characteristics that are determinant for interactions with living systems.
There is no clear opinion on which measures are most appropriate for assessing exposure. Also, there are no adequate portable instruments for measuring nanoparticle exposure. New sampling techniques and strategies for assessing exposure at the workplace and in the environment should be elaborated.
7.3 Currently, inhalation is the main route of human exposure to nanoparticles, and motor vehicle emissions constitute the most significant source of nanoparticles in urban areas. Exposure to airborne nanoparticles may also occur at some workplaces but data is scarce. Very little is known about the other routes of exposure, namely exposure through the skin (which concerns mostly cosmetic or pharmaceutical skin preparations that use nanoparticles) and exposure through ingestion.
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