When the impregnating spray hits your lungs

What happens if impregnating sprays containing tiny particles (nanoparticles) get into your lungs? Do they trigger inflammation in your lungs, or even cause damage to your lung tissue? These are key questions that have been addressed over the past three years by experts from Germany, other European countries and the USA as part of the "NANOaers" international research project, led by the German Federal Institute for Risk Assessment (BfR). The results of the tests on aerosols released from impregnating sprays were presented at the project's concluding workshop, held on 21 and 22 January 2020. A gas transports (either solid or liquid) airborne particles in an aerosol. The experiments involving silver or cerium oxide nanoparticles showed that it was not just the properties of the particles, such as their size, that influence the impact on lung tissue. The solvents and additives contained in these sprays also change the way the aerosols react with lung cells. Additives are substances that stabilise solutions and increase the dirt-repelling properties of the impregnating sprays.

Nanospray products are made up of particle-liquid mixtures, which are converted into aerosols when they are sprayed. Made up of minute airborne particle-liquid droplets, these products can get deep into the lungs when inhaling.

The core part of the NANOaers research project involved investigating the interactions between the various elements contained in nanosprays, such as solvents and additives, and the nanoparticles contained therein, as well as the resulting biological consequences. A method was also developed in order to depict, as realistically as possible, the impact of aerosols sprayed from spray cans on the respiratory tract and cells.

During their experiments, the researchers combined a spray chamber developed in-house with other equipment enabling a physical aerosol analysis and toxicity tests with cell cultures. This arrangement included physical measuring tools to examine the aerosols on the one hand, and an air-liquid interface, a device in which human lung cells come into contact with aerosols, on the other hand. Aerosols made up of the desired composition of particles, solvents and additives were created in the spray chamber. This enabled the scientists involved to analyse the impact of the individual components in a targeted fashion, doing so as if they came from a commercial spray can. The aerosol generated in this way was then transferred to the analysis chamber in order to be analysed. The size and volume of particles were measured there. A portion of the aerosol stream formed on the cell culture at the same time and reacted with the human lung cells. Finally, the extent to which the cells absorbed particles and the associated consequences of such absorption were examined. In doing so, signs of inflammation and their survivability were tested.

The tests involving silver or cerium oxide nanoparticles showed that only a portion of the aerosols from the spray chamber established on the cells. The question how large this portion is, depends on the composition of the nanospray solution, i.e. the respective solvents and the contained additives. However, the spraying method involved also plays a role here. A small number of brief sprays meant a lower rate of absorption by the cells. In addition, the distance from the spray can and the system ventilation are also key factors here; in a real-life application, this would involve the room size or any opened windows, for example. Furthermore, the tests showed that the damage caused to the cells by the aerosol is also largely determined by the solvents and additives used. In particular, the investigated perfluorosilane additives were found to be toxic to cells.

In addition to the BfR, the NANOaers project involved the Mechanical Process Technology working group from Technical University of Dresden, the Institute of Fluid Mechanics and Heat Transfer from Graz University of Technology, the Spanish GAIKER Technology Centre, Harvard University together with T.H. Chan School of Public Health in Cambridge, USA, and the Romanian National Research & Development Institute for Textiles and Leather. With NANOaers, the six institutes involved have created a test assembly that enables the realistic analysis with regard to the potential health risks of aerosols with nanoparticles as mixtures, without having to resort to animal experiments.

Funding for the NANOaers project for German partners has been provided by the Federal Ministry of Education and Research (BMBF), under the terms of the Horizon 2020 framework. The other European and international partners were funded via the ERA-NET SIINN research programme and national project sponsors.

About the BfR

The German Federal Institute for Risk Assessment (BfR) is a scientifically independent institution within the portfolio of the Federal Ministry of Food and Agriculture (BMEL) in Germany. It advises the German federal government and German federal states ("Laender") on questions of food, chemical and product safety. The BfR conducts its own research on topics that are closely linked to its assessment tasks.

This text version is a translation of the original German text which is the only legally binding version.

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