18 December 2008

Careful, nanoparticles!

Nanotoxicity"Everything in the world is poison, and only

the dose makes the substance safe"

The ability of harmless substances to become dangerous to health during strong grinding was discovered by mankind long ago, long before the advent of nanotechnology. Even in ancient times, people engaged in zinc smelting suffered from zinc fever caused by inhalation of zinc oxide aerosols. Everyone also knows the carcinogenic effect of asbestos dust, which causes lung and peritoneal cancer. But still, the most extensive damage to health is caused by the inhalation of carbon nanoparticles formed during incomplete combustion of organic fuel in car engines, at power plants, especially in large quantities entering the lungs of a person during smoking. The fact is that the protective mechanisms of the lungs are completely unable to process or remove carbon dust, and it remains there forever, causing reflex narrowing of the bronchioles and alveoli and reducing the amount of oxygen in the blood. It is also impossible not to recall that asbestos is prohibited for use in most developed countries simply because its microscopic fibers can cause serious oncological diseases when inhaled. In the era of the nanotechnology revolution, scientists, creating and using new nanomaterials, should feel responsible to society, learn to predict the impact of nanoparticles on human health and the ecology of the entire planet. To do this, you need to know the "toxicology of nanoparticles".

A characteristic feature of substances in the nanostate is the ability to “pass” through the body's defense systems. For example, particles smaller than a few hundred nanometers easily penetrate into the intra-pulmonary space, and nanometer particles freely enter the bloodstream from the lungs. This is how the influenza virus, which is a complex natural nanoparticle, enters the human body.

If the penetration of nanoparticles into the lungs occurs, as a rule, against our will, then we apply them to the skin voluntarily and with great pleasure – nanoparticles are a key component of most all kinds of creams recommended by dermatologists and cosmetologists. Indeed, creams for "rejuvenation" of the skin contain nanoscale liposomes, and topical sunscreen creams during the summer holidays are highly effective nanoparticles of titanium oxides TiO 2 and zinc ZnO, absorbing the UV part of the solar spectrum. However, almost no one thinks about the fact that nano-TiO 2 penetrates into the skin and is found in the epidermis already 8 hours after applying the cream. It is not surprising that since the beginning of the mass use of such creams, the incidence of skin cancer, for example, in the USA has increased by 90%! Unlike the respiratory system and skin, the behavior of nanoparticles in the gastrointestinal tract has been little studied - it is only known that they are rapidly excreted from the body.

Based on the knowledge accumulated to date about the properties of various nanoparticles, three main reasons for their harmful effects on human health can be identified. Firstly, the main substance of a nanoparticle can be toxic, as, for example, in the case of "quantum dots" – Cd 2+, whose toxicity is high both in the nano- and macro-states, is the cause of toxicity for individual cells of water-soluble cadmium selenide CdSe nanoparticles. At the same time, the cytotoxicity of CdSe correlates with the amount of cadmium released from them during oxidation, and can be significantly reduced when coated with ZnS or SiO 2. As another example, ultrafine particles of beryllium oxide, as well as metallic beryllium and its compounds, the inhalation of which causes a slowly developing lung disease with a fatal outcome – beryllosis. While compact beryllium oxide BeO is an exceptionally inert and harmless material, highly reactive nanoparticles of this oxide, entering lung cells, give a soluble phosphate complex Be 2+, which inhibits phosphatase and causes cell death.

Secondly, even if the nanoparticles that have entered the body are harmless in themselves, some of them can act as catalysts for the formation of toxic substances. This is how the TiO2 and ZnO nanoparticles discussed above behave, catalyzing photooxidation, viruses, nanoparticles of iron oxides and some other metals that cause metallic (in particular, zinc) fever.

And, finally, the specific effect of the substance on the body can be directly due to the fact that it is in a nanostate. For example, the chemically inert and safe polymer fluoroplast, widely used for the manufacture of tableware, being sprayed in the air in the form of nanoparticles with a diameter of 26 nm in a negligible concentration (60 micrograms/m3) is able to kill a rat in 30 minutes, causing hemorrhages in the lungs. It may be hard to believe, but fluoroplast nanopowder is an order of magnitude more toxic than the VX chemical warfare agent! And the inhalation of aerosols of silicon dioxide nanoparticles SiO 2 causes silicosis – chronic destruction of the lungs, while in the macrocrystalline state it is absolutely safe – it is the most common sand that beaches are covered with and children's sandboxes are filled with. Thus, the specificity of nanoparticles consists in the large role of the surface, the chemistry of which (broken bonds, adsorbed molecules) is radically different from the chemistry of bulk material – for the same substance, small nanoparticles are more toxic than large ones. In addition, having penetrated into the cell, nanoparticles are able to adhere to various organelles and deform DNA, causing structural destruction and mutations.

The shape of nanoparticles has a certain value in nanotoxicity. Anisotropic nanoparticles (e.g. asbestos fibers) are associated with an increased risk of fibrosis and lung cancer. An aerosol of "carbon nanotubes" leads to the germination of fibers and thickening of connective tissue in the lungs of mice. Getting into the epidermis, nanotubes cause the release of cytokine by skin cells, which is a modulator of inflammatory processes.

In conclusion, I would like to draw attention to the words of Paracelsus given in the epigraph. Even such a useful substance as oxygen in large doses is poisonous – after three days in an atmosphere of pure oxygen, a person dies from pulmonary edema. For most nanoparticles, toxic doses are unknown, one can only hope that they will be determined in the future, but for now, elementary caution should be observed when working with such objects.

LiteratureG.Oberdörster, E.Oberdörster, J.Oberdörster, Nanotoxicology: an emerging discipline from studies of ultrafine particles, Environmental Health Perspectives, 2005, v.113, 823

P Hoet., I.Bruske-Holfeld, O.Salata, Nanoparticles – known and unknown health risks, J. Nanobiotechnology 2 (2004) 12


Portal "Eternal youth" www.vechnayamolodost.ru18.12.2008

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