The terms nanoparticles or nanoparticles denote compounds of a few to a few thousand atoms or molecules . The name nano refers to its size, which is typically 1 to 100 nanometers : One nanometer (abbreviation: nm ) corresponds to 10 −9 = 0.000 000 001 meters = 1 billionth of a meter. According to ISO / TS 27687: 2008, nanoparticles are nano- objects with three external dimensions. “Nano” is derived from the Greek “nanos” for “dwarf” or “dwarfish”.
Occurrence and manufacture
Synthetic nanoparticles are artificially produced particles that are specifically equipped with new properties and / or functionalities, such as. B. electrical conductivity, chemical reactivity. Synthetic nanoparticles can be subdivided according to their chemical and physical properties. Groups that are widespread in research and application are:
- Carbon-containing nanoparticles
- Metal and semi-metal oxides ( silicon dioxide (SiO 2 ), titanium dioxide (TiO 2 ), aluminum oxide (Al 2 O 3 ), iron oxides (Fe 2 O 3 or Fe 3 O 4 ), zinc oxide (ZnO) as well as zeolites and others on silicon based mesoporous materials such as MCM-41 or SBA-15 )
- Semiconductors ( cadmium telluride (CdTe), cadmium selenide (CdSe), silicon )
- Metals (gold (Au), silver (Ag), iron (Fe))
- Metal sulfides
- Polymers such as dendrimers and block copolymers
Carbon-containing nanoparticles can exist in different forms:
While fullerenes and nanotubes are produced synthetically and are therefore clearly defined in their structure (e.g. Buckminster fullerene of 60 carbon atoms), industrial soot is understood to mean only very small carbon particles, B. can also arise in combustion processes. There are many possible areas of application for nanoparticles. So they could z. B. can be used to improve various materials in the household. In medicine, nanoparticles could be used to achieve a targeted transport of drugs in the body or a gentler form of cancer therapy. Nanoparticles could also help in electrical engineering, e.g. B. to enable more powerful and smaller computers.
The high potential benefits result in a drastic increase in the production and use of the most varied types of nanoparticles, but it also opens up a wide range of possible dangers for us and our environment. It is still extremely unclear which nanoparticles have an effect on organisms. In order to be able to estimate the possible hazards that the nanoparticles pose to the environment during their production, use and disposal, nanoecotoxicology was established. It emerged in addition to the ecotoxicology that already existed up to that point , since nanoparticles have novel chemical and physical properties.
Properties of nanoscale particles
Nanoparticles have special chemical and physical properties that differ significantly from those of solids or larger particles. These are among others:
- higher chemical reactivity possible due to large specific surface (large particle surface in relation to volume)
- low influence of inertia forces (weight force) and increasing influence of surface forces (e.g. van der Waals force )
- increasing importance of surface charge (see DLVO theory ) and thermodynamic effects ( Brownian molecular motion )
- this can result in stable suspensions but also aggregate formation
- special optical properties
Ultimately, these properties of the nanoparticles are based on the extremely high surface charge that seeks compensation. However, this increased reactivity limits the service life as “singular nanoparticles” to a very short time. If there is no targeted isolation through ion or micelle loading , charge equalization through agglomeration or aggregation (e.g. through ultrasound irradiation and vortexing ) occurs very quickly , which according to the 2nd law of thermodynamics only occurs with the use of correspondingly high energy inputs can be solved again. This lifetime of singular nanoparticles can represent a criterion in the risk assessment and occasionally exclude the inclusion of nanostructured materials in risk assessments.
Graphite is (a form of carbon, in addition to diamond and fullerene), the basic structure of carbon black ( carbon black ). It is a soft, shiny black metallic material that occurs both naturally and can be artificially produced. The crystal structure of graphite consists of many parallel layers on top of one another, which can vary in size and arrangement. Within these layers, sp 2 -hybridized carbon atoms condense into aromatic six-membered rings and form a conjugated π system.
Carbon black is the English name for industrial soot that is specifically manufactured under controlled conditions and is physically and chemically defined. On the other hand there is chimney or diesel soot, which is a by-product that is not precisely defined when coal or hydrocarbons are burned.
Carbon black consists of 96–99% carbon, the remaining parts are hydrogen, oxygen, nitrogen and sulfur, most of which (in functional groups) are chemically bonded to the surface. The surface energy is greatest at the corners and edges of the aromatic compounds, so that adsorption of gases and liquids takes place preferentially.
The oxide groups on the pore surface have the greatest influence on the physicochemical properties of industrial soot, such as water adsorption and catalytic, chemical and electrical reactivity. Mainly, basic hydroxyl, acidic carboxy as well as carbonyl and lactone groups are formed on the surface. In the production of active carbon black, functional oxygen groups can be introduced with a mass fraction of up to 15%.
In air quality measurement, particles with a thermodynamic diameter of less than 0.1 µm are referred to as ultra-fine particles (UP or UFP, "ultra-fine dust"), regardless of their precise nature . The thermodynamic diameter describes a spherical particle with an identical diffusion behavior as the considered particle.
The fullerenes are brown-black powders with a metallic sheen. They dissolve in some organic solvents (e.g. toluene ) with a characteristic color. Fullerenes change from solid to gaseous at approx. 400 ° C.
Semiconductor nanoparticles have special fluorescence properties . As with macroscopic semiconductors, there is a band gap ; This means that excitons (electron-hole pairs) can be generated by optical excitation , which emit photons upon recombination, i. i.e., emit light in the form of fluorescence. What is special about semiconductor nanoparticles is that the energy of the photons (i.e. the energy difference between the ground state and the excited state) does not only depend on the material, but also on the particle size. In this way, particles can be produced from the same material, which fluoresce in different colors, whereby the color (emission wavelength ) can be adjusted through the particle size. Small particles emit at shorter wavelengths (greater photon energy), larger particles at longer wavelengths (smaller photon energy). This can be explained by quantum mechanics ("" " Particle in the Box " model), even in the simplest model it becomes clear that due to the spatial restriction (the electrons must be inside the particle) the distance of the energy levels from the spatial dimensions (i.e. the Such systems are also known as quantum dots , common materials are e.g. CdSe and CdTe . Oxide materials have a very large band gap and are optically transparent. They can be made to phosphorescence by doping them with foreign atoms .
Carbon nanotubes (English: carbon nanotubes , CNT ) consist of cylindrical graphite plies and have a diameter of 1-100 nm The shape of the nanotubes can be single-walled, multi-walled or Y-shaped.. They show u. a. have a very high thermal conductivity , high tear resistance and extreme elasticity , and they are also very hard-wearing. They have ten times more tensile strength than steel . Depending on the detail of the structure, the electrical property inside the tube is conductive or semi-conductive.
Compared to metals in larger configurations, metallic nanoparticles have changed chemical properties. This is due to their smaller size and the resulting very high surface-volume ratio. So z. B. colloidal gold has a stronger catalytic activity and shows, with very small gold nanoparticles, a drastically lower melting point .
In addition, alkali metal, copper, silver and gold nanoparticles show different optical properties compared to the same metals in larger arrangements. In dispersion they show a broad absorption band in the visible range of the electromagnetic spectrum and thus have an intense color (characteristic color of gold colloids : red to purple). This effect is caused by particle plasmons.
In biochemistry and cell biology , nanoparticles are used for uptake in cells . To change the function of the nanoparticles and to avoid aggregation, these particles are coated, e.g. B. for binding proteins in the immunogold staining used for transmission electron microscopy or for binding DNA in the ammunition of the gene gun .
The end of 2013, researchers succeeded in the United States of America for the first time, stable nano water to generate -Tropfen - with a diameter of 25 nanometers. This was achieved by means of electrospray . Due to the increased surface tension compared to normal water droplets, the nano water droplets remained stable for up to four hours and were able to float in the air for a certain time without evaporating. In addition, highly reactive oxygen radicals such as hydroxyl radicals and superoxides that were generated during the splitting of the water by the electrospray process were encapsulated in the nanodrops. Because of the additional ionization, the drops were extremely aggressive: they tore holes in the cell membrane of bacteria floating in the air, killing them in this way. This process led to the formation of the term nanobomb for the water particles . As a result, the use of nanowater as a - completely residue-free - disinfectant was discussed. In inhalation experiments with mice, a toxicological effect was e.g. B. not found in their lungs, since the nanowater particles would presumably be neutralized immediately on aqueous surfaces. "
Differentiation from aerosol
Aerosol is the collective name for the finely distributed (dispersed), solid and liquid particles (suspended matter) of different sizes that are floating in gases. The same laws of nature apply to nanoparticles suspended in the gas - regardless of whether they were created intentionally or unintentionally.
Nanoparticles in aerosols have z. T. a short service life of only a few hours, since they coagulate quickly with larger particles due to their high diffusivity .
Completely new aerosol particles can form in the atmosphere. Experiments in the expansion chamber made it possible to study aerosols in the nanometer range from one to three nanometers and to simulate the formation of new aerosol particles in the atmosphere.
The range of aerosol nanoparticles from 1 to 10 nm is of particular interest, since quantum effects occur in this order of magnitude and the formation of critical clusters and subsequently larger aerosol particle molecules can be observed. Above a certain particle size, they become less volatile and condensation nuclei on the order of 100 nm can develop.
Various processes for the production of nanoparticles have become established: A distinction is made between bottom-up and top-down processes, depending on whether a material is nanostructured (top-down) or e.g. B. Particles are synthesized from a fluid phase.
- Grinding processes
- Laser ablation
or via lithographic processes such as:
- Electron beam lithography
- Nano imprint lithography
- chemical production in solutions (e.g. sol-gel method ),
- Production in plasma , with gaseous starting materials , alternatively also by means of a heated reactor (e.g. chemical vapor deposition ),
- Production by self-organized diffusion-limited growth on surfaces or with templates (e.g. hydrothermal synthesis of nanoporous cetineites ),
- Production through targeted nucleation of molecules from the gas phase (aerosol process).
- Microemulsion techniques
- SMAD ( solvated metal atom dispersion )
Depending on the area of application of the nanoparticles, a precisely defined and narrow particle size distribution is usually required. Depending on the chemical nature of the desired nanoparticles, one or the other method is better suited to achieve a good result. Mostly, methods in solution or methods of self-organization deliver the best results. However, these are difficult or impossible to carry out on an industrial scale.
It has been possible to create logic circuits from carbon nanotubes and from semiconductor nanocables. These could be the first steps towards making nanocomputers a reality. In addition, the first logic circuits with zinc oxide nanoparticles could be demonstrated. Due to the permeability for electromagnetic waves in the visible wavelength spectrum, these circuits are particularly interesting for the implementation of transparent electronics. In addition, the zinc oxide can also be deposited in its nanoparticulate form in printing processes, so that circuit integration in the printing process is possible. However, since the performance is reduced by the relatively low charge carrier mobility, the components are mainly suitable for so-called low-cost / low-performance applications. This includes, for example, RFID tags or simple sensory tasks. Indium arsenide nanocrystals are used to make light emitting diodes (LEDs). The radiation wavelength is that of telecommunication systems. One area of application could be telecommunications technology.
Nanoparticles are already used in the manufacture of many products. Concrete is sometimes mentioned as the oldest nanomaterial , although it was only recognized long after its first use that it owes its strength to crystal structures that are only a few nanometers in size. Whether "marble from the roll", facade plaster that removes pollutants and unpleasant smells by adding nanoparticles or nanoparticles on roof tiles that are supposed to prevent the growth of algae - there are many ways to improve materials with the help of nanotechnology.
A number of cosmetic products, such as various sun creams, deodorants and toothpastes, contain nanoparticles such as titanium dioxide (TiO 2 ) ( E 171 ) and aluminum oxide (Al 2 O 3 ). Nanoparticles are already being buried in food. In tomato ketchup , silicon dioxide (E 551) is used as a thickening agent, titanium dioxide is used to lighten salad dressings and aluminum silicate counteracts the clumping of powdered foods.
The NanoEnergieTechnikZentrum (MAINS) researches with nanocomposites for more powerful electrodes of lithium-ion batteries that have a higher through the relatively larger reactive surface of the nanocomposites energy density and power density can be obtained.
Further examples are nanoparticles in paints and varnishes as well as impregnating agents for all types of surfaces, which are supposed to offer protection against mechanical damage.
In October 2009 the Federal Environment Agency warned of health risks that could result from the industrial use of nanotechnology in food, clothing, cosmetics and other products. Shortly afterwards, however, the Federal Environment Agency put its statements into perspective again. Leading Swiss scientists were also surprised by the statements made by the Federal Environment Agency in its study from October 2009. Nevertheless, Bio Suisse ended the approval of E 551 as a release agent in spices at the beginning of 2019 due to concerns about the nanoparticles it contains.
Nanotechnology in Medicine
Nanotechnology opens up a wide hypothetical field for medical applications.
- One example is the growth of artificial bones through the implantation of coated titanium frameworks on which the bone component hydroxyapatite can be deposited. In addition, a bone substitute material has been developed which consists of hydroxyapatite. Due to the nanocrystalline structure of the substitute material, bone-forming cells can immigrate and replace the bone substitute mass with natural bones.
- The special properties of nanomaterials can be used to specifically make the blood-brain barrier passable for therapeutic agents. The targeted introduction of drugs into the body could also be made possible by nanotechnology. The tissue-specific treatment is intended to achieve minimal side effects. The surface quality of the injected substance is decisive for its further purpose in the body. Particles with a water-repellent surface are quickly recognized and removed by the immune system. This process can be circumvented by coating the particles with molecules that are not recognized as foreign by the immune system. An example of this is the injection of liposomes (microscopic bubbles made of phospholipids ) that have been coated with certain molecules. Liposomes can be used, for example, in cancer therapy, since the blood vessels of tumors have a greater permeability ( EPR effect ) for the liposomes than the blood vessels in healthy tissues. The liposomes thus accumulate in the tumors. In this way, active ingredients can be used in a targeted manner.
- Among other things, cells have a mechanism for absorbing substances called receptor-mediated endocytosis (see membrane transport ). Here, receptors on the surface of the cells have the function of recognizing substances with suitable surface molecules and initiating the uptake of the substance into the cell. The receptors vary from cell type to cell type or from tissue to tissue. If the desired substance is coated with biomolecules, such as. B. monoclonal antibodies (see antibodies ) or sugar residues - which can have highly specific properties and can therefore only be recognized by certain cell receptors - it is possible to direct the substance into a very specific body tissue.
- Targeted marking of certain cells (e.g. stem cells, dendritic cells), for example with nanoparticles of iron oxides, allows the cells administered for therapeutic purposes to be displayed non-invasively using imaging techniques such as magnetic resonance tomography at different times.
- The first cancer treatment with nanoparticles made from paclitaxel albumin has already been approved with the drug Abraxane (manufacturer Celgene ) for metastatic breast cancer . Cancer treatment with iron oxide nanoparticles is another research area (see nanotechnology ).
- With bovine sperm stored in magnetically influenceable nanoshells, so-called “assisted” artificial inseminations are achieved under laboratory conditions .
The diverse fields of application of nanotechnology also open up new possibilities for use in the military sector. For example, small, built-in computers in weapons or uniforms are conceivable, as is the implantation of nanotechnology in soldiers' bodies, for example for communication, monitoring or the dispensing of medication. Likewise, new applications are foreseeable in the field of biological and chemical weapons, also for detection and medical treatment.
The relationship between the benefits and dangers of nanotechnology is controversial. The technology could offer potential for relieving the burden on the environment, but many of the applications are still in development.
- Nanomaterials can be used as binders for environmental toxins. For example, two minerals occurring as natural nanoparticles ( allophane and a smectite ) have been shown to have a high absorption capacity for pollutants such as B. have copper or naphthalene .
- From Rice University a low-cost removal (filtering) was of arsenic from drinking water using nano magnetite developed.
- Nanotechnology-based sensors should be very energy-efficient to operate because of their lower weight. These sensors are primarily developed for the biomedical and military sectors. They can also be used in environmental applications for the optimized and specific detection of biological and chemical contamination.
- With the use of nanotechnology-based light-emitting diodes (LED), it is said that a three to five-fold increase in energy efficiency can be achieved for lighting compared to lighting with conventional compact fluorescent tubes. According to the UBA, the use of dye solar cells promises a higher efficiency of light capture through nanometer-fine distribution of a light-absorbing dye.
- The water quality can also supposedly be improved. By using nanotechnology-based flow condensers for seawater desalination, more than 99 percent of the energy to be applied should be saved compared to conventional reverse osmosis or distillation. In wastewater treatment, pretreated wastewater can be freed of pathogens through nanoporous membranes, thus preventing their spread in the environment.
- Silicon dioxide and nano-soot particles are already incorporated into modern car tires to reinforce the material. They are supposed to bring about a lower rolling resistance and thus help to save up to ten percent fuel.
- The exhaust gas cleaning in motor vehicles is to be improved by nanoporous filters in order to hold back soot particles from exhaust gases.
- In pest control, ultra-thin nanopolymers could replace toxic organic biocides.
- By reducing the layer thickness of paints, raw materials can be saved. Furthermore, chrome VI paints, which are harmful to the environment and health, could allegedly be dispensed with for corrosion protection for metals because of nanotechnology-based surfaces. The use of nanoparticle-containing car paints promises less wear and tear due to the ceramic-like crystalline structure of several wafer-thin layers. According to Mercedes, this nano-paint, which has already been used for two years, still has 72 percent “residual gloss” after around 100 car washes, whereas conventional paint only has 35 percent of the new car's brilliance with the same load. This varnish therefore helps to ensure that you do not have to wash your car as often and thus save water and contaminate the groundwater less. According to the manufacturer, there is no health risk because the nanoparticles are bound in a matrix. Similar nano lacquers are also used as wall paint.
According to an article by the Federal Ministry for the Environment (BMU), considerations about the disposal of nanoparticles are still marked with a question mark. When creating disposal guidelines, it must be taken into account whether the particles are free or bound to a matrix , whether they are water-soluble or not, whether they disintegrate or agglomerate. There is no such thing as “the nanoparticle”, each substance must be viewed individually, and for this purpose the various particles must first be characterized and standardized .
So far, there is little experience or knowledge on the disposal of nanoparticles. First scientific investigations in connection with their combustion showed that they largely did not get into the exhaust gas stream, but remained in the respective ash and slag. Further investigations are in progress: For example, it is unclear what happens to nanoparticles from cosmetics , for example, that have got into the water or sewage sludge .
The enormous reactivity of nanoparticles and the drastic increase in the production and use of the most diverse types of nanoparticles can open up a broad spectrum of possible dangers for humans and the environment. The expansion of the product range for the benefit of the consumer can bring great advantages, but the advantages and disadvantages of the nanotechnologies already used and the materials used must be carefully weighed. In a study, the Federal Environment Agency recommends avoiding products with the small particles as long as their effects on the environment and on human health are still largely unknown. A Japanese study concluded that nanoparticles can affect brain development in fetuses. Several animal- based studies have repeatedly shown that nanoparticles cause inflammation of the lungs .
Numerous studies show possible environmentally damaging and unhealthy aspects of nanotechnologies, for example the absorption of the particles into the organism via the respiratory tract, skin and mouth, even in products such as cosmetics and food additives that are already on the market. There is no evidence of any risk to humans or the environment from the nanomaterials currently in use. Conversely, however, it cannot be assumed that they are generally harmless, according to the Federal Environment Agency in 2016. From a scientific point of view, however, nothing speaks against the fact that nanomaterials can be awarded eco-labels .
Due to their small size and the associated special mechanical properties (ability to clump), nanoparticles such as titanium dioxide have been shown to be toxic in tests in a manner that was previously not detectable and recorded.
Risks to humans
Due to their small size (10–100 nm), nanoparticles can be absorbed into the body via the skin, the respiratory tract (cf. inhalable fraction ) and via the gastrointestinal tract, where they are distributed throughout the entire organism via the bloodstream.
During the production, consumption and use of products containing nanoparticles, people come into contact with these potentially harmful substances. If the particles are absorbed into the organism, they could cause considerable damage there and be the cause of diseases. Numerous studies are being carried out to this end, which aim to expand current knowledge of the toxicology and ecotoxicology of nanomaterials. Any risk to workers in the manufacture of nanomaterials can be ruled out if the applicable workplace safety rules are followed.
Basically, it must be pointed out that in investigations carried out so far, no uniform standards have been applied for the characterization of the materials used and for carrying out the measurements. Research projects such as the NanoCare project supported by the Federal Ministry of Education and Research provide the first binding work instructions .
- When using nano impregnation sprays, for example, nanoparticles can be absorbed into the lungs through the air we breathe . In the lungs, nanoparticles reach the area of the alveoli, in contrast to larger particles. There they become the trigger for severe inflammation of the lung tissue. In addition, the transfer of the particles into the bloodstream also takes place at this point. Smaller particles pass more easily into the blood and can then penetrate the blood-brain barrier.
- In a study published in 2009 studying the effect of carbon nanotubes on the lung tissue of mice was clear that the tubes such as asbestos fibers to the pleura penetrate. Scavenger cells of the immune system subsequently gathered there , two weeks after inhaling the fine dust (in a single, high dose), scars formed on the lung tissue, so the tissue was irritated. Researchers follow the same precautions as when using asbestos until the risk is more clearly identified.
- Basically, it has been proven that nanoparticles that are absorbed through the olfactory mucous membrane reach the brain via the nerve tracts of the olfactory bulb and through the extremely selective blood-brain barrier. The protection of the brain from highly reactive and presumably tissue-damaging substances is therefore no longer guaranteed due to the size of the nanoparticles.
- As a result of the uptake of nanoparticles, especially in people suffering from arteriosclerosis and heart disease, the existing disease can worsen and there can be deposits in various organs such as the spleen, liver, bone marrow, etc.
- The consumption of foods that contain nanoparticles enables the potentially harmful substances to be absorbed into the bloodstream via the mucous membranes of the gastrointestinal tract. In the intestine, nanoparticles are absorbed by Peyer's plaques . When nanoparticles are absorbed via the gastrointestinal tract, the smaller the particles, the greater the likelihood that the absorbed particles will deposit in certain tissues and organs and cause damage to them.
- Another possibility for the absorption of nanoparticles into the organism is possibly via the skin, e.g. B. by the direct application of nanoparticle-containing cosmetics. Some studies refute the uptake of nanoparticles up to living cell layers of the epithelial tissue; other studies give indications to the contrary. For example, nanoparticles contained in cosmetic products could be absorbed into the skin directly via the cornea or via hair roots and lead to damage to the cells there due to the formation of radicals and possibly trigger skin irritations and allergies. However, recent studies using modern methods have shown that the dermal absorption of nanomaterials, if they are used in cosmetics, is very low, if at all. The Scientific Committee on Consumer Safety (Scientific Committee on Consumer Safety, SCCS) at the European Commission has fundamentally concerned with the safety issues of nanomaterials in cosmetics and came to literature review concluded that usually a simplified procedure for the assessment of nanomaterials can be used in cosmetics when applied to the skin and has justified this in a detailed statement. Also for some nanomaterials, such. If, for example, they are used in sunscreens as effective physical protection against sunlight, detailed statements by the SCCS are available that prove the harmlessness of their use in cosmetics. This scientifically based safety is a prerequisite for approval and inclusion in the corresponding appendices of the European Cosmetics Regulation 1223/2009 / EC, e.g. B. for nano-titanium dioxide, nano-zinc oxide and another nanomaterial on an organic-chemical basis (tris-biphenyl-triazine), while nano-carbon black is approved as a coloring agent in cosmetics after an appropriate assessment by the SCCS. However, the SCCS did not classify the inhalation of the aforementioned nanomaterials as harmless due to unexplained possible risks. This is why the use of these nanomaterials in pressurized gas spray cans is currently not permitted.
- “Nanoparticles used medically can damage DNA without having to penetrate the cells. This is shown by a study on cells kept in culture that has now been published in "Nature Nanotechnology". "
- One study found that nanoparticles that got into the bloodstream were enveloped in a protein corona , a ring of up to 300 endogenous proteins , within seconds due to their molecular attraction ; this corona practically did not change after its formation. The effect in the body remained unclear.
Risks to the environment
It is not clear whether these ecological risks and dangers also apply to nanoparticles introduced into carrier substances (lacquers, facade paints, textiles) or technical devices (information technology). The current state of science does not permit any reliable statements to be made about the danger and harmfulness to health with regard to nanoscale ingredients and components. It remains to be clarified whether, due to certain weather conditions or mechanical stress, nanoparticles can escape from facade paints, car tires or paints in the form of nanoscale abrasion.
If nanoscale particles are washed out from solid carrier substances, this can pollute the environment and organisms. The use of nanoscale compounds is very likely synonymous with their entry into the environment or their entry into food chains. Even if the nanomaterials as such do not cause any direct damage, nanoparticles could, due to their high reactivity, bind other pollutants and facilitate their transport in the air or in water.
The hazard potential is mainly due to the binding to and from toxic substances, the mobilization of heavy metals, binding of nutrients in the groundwater, accumulation via the food chain, worldwide distribution via the air and changes in the microfauna due to biocidal effects in soil and water.
The behavior of nanoparticles in the air is discussed in more detail in the section “Risks during manufacture”.
In water, too, particles can fundamentally change their properties due to the binding of other substances so that, for example, their absorption by organisms would be facilitated: Either the particles themselves or pollutants bound to them could trigger negative effects in the organisms. The biological activity of the nanoparticles depends on their size, shape, chemistry, surface and solubility.
A study by Ling Yang and Daniel J. Watts from the New Jersey Institute of Technology provides indications of the negative or inhibitory effects of nanoparticles on the root growth of plants. There is a need for further clarification here.
Studies with fish indicate that nanoparticles can also penetrate biological barriers such as the blood-brain barrier. The so-called C60 molecules (also known as “Buckminster fullerenes”) are absorbed through the gills at relatively low concentrations. The distribution of the nanoparticles in the body seems to be dependent on size, shape and material properties. Experiments by Swedish researchers suggest that commercially produced polystyrene nanoparticles that are ingested through the food chain can influence the eating behavior and fat metabolism in fish.
In a cross-generational experiment with water fleas it was found that the offspring of animals treated with titanium dioxide, which themselves never had contact with titanium dioxide , were more sensitive to the substance: they did not shed their skin as usual or died; there must have been “a transmission of damage from parents to subsequent generations”.
When manufacturing nanoparticles, there is a risk of people being exposed at their workplace, because knowledge of the actual behavior of nanoscale substances is so poor that it is not possible to set up meaningful MAK or TRK values to a satisfactory extent. This ignorance of the general chemical and physical properties of particles of this size and also the lack of ethical debate in this area will possibly lead to the "accidental" production of highly dangerous substances that cause great damage to exposed organisms.
Faults in the apparatus can cause nanoparticles to be released into the environment during their synthesis. Such an accident is much more difficult to determine than with larger particles because the concentrations in which nanoparticles are present are usually very low. Nanoparticles move very quickly and can travel long distances in the air. They are thus distributed in the room in a very short time, so that not only areas in the immediate vicinity are contaminated, but also areas and people further away. Highly sensitive gas detection systems are required for control.
At the moment there are neither suitable masks nor high-performance filters available that offer adequate protection to those directly exposed. Although nanoparticles are subject to a rapid growth process due to collision and agglomeration, the aggregated particles are mostly still nanoparticles.
In the near future, production will be followed by long-distance transport of nanoparticles. Accidents, such as a leaking or sinking oil tanker, transferred to nanoparticles, currently possibly catastrophes of unpredictable proportions.
The production of large quantities of substances such as nanoparticles must result in a targeted disposal management and policy with particular attention to the chemistry and reactivity of the material to be disposed of. In addition, safety standards both during manufacture and during transport must be based on the hazard potential of the substances in question. This is not possible with regard to nanoparticles, since the range of products is already much larger than the range of the examined nanoparticles.
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