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What do we know about the long-term effect of manufactured nanoparticles found in nature?
Manufactured nanoparticles, that is to say made by humans, are today present in a multitude of consumer products, from cosmetics to paints, including clothing and flat screens. These nanometric-sized particles (of the order of a nanometer, or 10-9 meter) end up one day or another being released into the environment. We therefore find them everywhere, in the air, in water, in river sediments and in soils where they are very difficult to detect.
“The toxicity of these nanoparticles depends above all on their composition, which closely resembles that of the elements that compose them. A nanoparticle made of cadmium will have the same effects as an equivalent concentration of cadmium in ionic or metallic form,” underlines Kevin James Wilkinson, professor in the Department of Chemistry at the University of Montreal and deputy editor-in-chief of the journal. Environmental Science: Nanoof the Royal Society of Chemistry.
Toxicity therefore varies from one type of nanoparticle to another. For example, silica nanomaterials (SiO2, which has the same chemical composition as sand), which are introduced in particular in food, baby diapers as well as cosmetic and pharmaceutical products and toothpastes, are much less toxic than quantum dots. The latter, crystalline nanostructures of semiconductors, are used in the manufacture of flat TV and computer screens in particular, and are made up of cadmium and selenium surrounded by zinc sulphide, explains the professor.
“We cannot simply say that all nanoparticles are toxic. It would be like saying that all metals are toxic. There are certain metals that are beneficial to the body, such as zinc and iron, which are included in the composition of certain vitamins,” notes Kevin James Wilkinson.
Zinc, iron and copper may be beneficial at low concentrations, but they become toxic at high concentrations. Therefore, given that the quantity of nanoparticles continues to increase in the environment, is there not a risk that those containing these metals reach a toxic abundance?
“There is indeed this risk that we exceed the toxic threshold, but for the moment, according to the measurements that we have taken to evaluate the toxicological risk of nanoparticles in the environment, we do not find, in any way general, concentrations which are very worrying, apart from the cases of contamination by an industry which produces it or which pollutes”, affirms the specialist in environmental chemistry.
The assessment of the toxicological risk of each type of nanoparticle consists of dividing the concentration found in the environment by that where negative effects have been observed in the laboratory. For the moment, the concentrations measured in the environment seem 10 to 100 times lower than the concentrations recognized as toxic, specifies the researcher.
Only a few particular types of nanoparticles seem a little more problematic than others: this is particularly the case for titanium dioxide (TiO) nanoparticles.2), the concentrations of which could approach the toxicity threshold, because these nanoparticles are present in particular in paints, which means that all or almost all surfaces are covered with them. “Titanium dioxide is also a persistent compound, it does not degrade and accumulates in the environment. Its presence therefore entails a longer-term risk,” adds the specialist.
Silver nanoparticles, which are found in cosmetics, deodorants and socks due to their antibacterial properties, can also prove problematic due to their abundance in the environment, and the fact that they could dissolve there more easily and thus end up in a toxic ionic form.
Nanoplastics, on the other hand, do not degrade well and persist in the environment. Their toxicity is mainly attributable to the products that are added during their manufacture in order to give them a flexible or rigid texture, or even a particular color. These products are often 1000 times more toxic than plastic.
The case of nanopesticides, that is to say these organic nanocapsules into which pesticides are introduced, which make it possible to better target the plants that we aim to exterminate and thus to reduce the quantities of pesticides introduced into the environment, has was studied by Mr. Wilkinson’s team. This analysis found that nanoparticles were much less problematic than the pesticides they contain.
How do nanoparticles with toxic potential exert their harm? Their very small size allows them to cross the biological membranes of cells and gives them a large surface area which increases their chemical reactivity, explains the researcher.
In the absence of regulations aimed at reducing the use of nanoparticles, it is essential to monitor their presence in the environment, says Mr. Wilkinson.
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