I, for one, and I am sure many similarly, simply do not think about the air quality once the vessel is closed and the process commences. So what has changed now? Well it is the increasing use of nano-materials that has brought into focus the potential dangers. Nano-materials by their definition are of the nanometer scale, often in all three dimensions. The significant part of this is that they are orders of magnitude below a size that can be resolved by the human eye. In many cases they are small enough that they are easily moved around in the atmosphere and are slow to settle onto surfaces. This means that after cleaning a vacuum system the nano-particles from the cleaning process will be present in the atmosphere and these will be present for days, if not weeks in the atmosphere unless the atmosphere is changed regularly. I have seen this happen in practice during a time when I was involved in the manufacture of a vacuum coated material used as a colored pigment. This pigment was in the micron range but due to the process a lot of fines were produced. The systems were cleaned and everyone wore protective clothing and masks. Once the cleaning was over the protective clothing and masks were discarded. Over the period of a couple of weeks it became noticeable that the top surfaces of all the equipment was changing color and when examined this was found to be due to the sub-micron particles of the pigment that had very slowly deposited out of the atmosphere. The worrying part about this was that this was the same atmosphere that we had been breathing. This demonstrable evidence comprised only the heaviest airborne particles and the expectation, although never proved, was that the atmosphere contained and even larger number of smaller particles that had not yet settle due to the continuous disturbance of the air.
The other item that reminded me of this hidden problem was an article I saw "Unveiling the molecular structure of pulmonary surfactant corona on nanoparticles," by Prof. Yi Zuo of the University of Hawaii. This explains a new method that Yi Zuo has developed to show the nano-bio interactions that take place in the lungs. This work shows that the inhaled nanoparticles that enter the lungs are coated in a natural pulmonary surfactant comprising lipids and proteins that enable the nanoparticles to stick onto the alveoli surfaces. This surfactant helps to minimise the work done when breathing and so any change to the quality of the surfactant can result in breathing problems. The surfactant easily sticks to the nanoparticles surfaces because of the high surface free energy of the nanoparticles and so it does not matter if the particles are silver or polypropylene the surfactant will cover them both. This means that instead of the particles being breathed in and then back out there is the possibility that they will be breathed in and stay on the lung surfaces and with the next breath more will be added. What happens then and just how far the nanoparticles can move through the body is a subject that is being actively researched. Any accumulation is likely to change the surfactant properties as well as allow the nanoparticles to move more easily over the lung surfaces to the bronchioles, the alveolar ducts and the alveoli. Particles in the surfactant could potentially cause a reduction in the gas diffusion and hence gas transfer that takes place across the alveoli which would be felt as breathlessness. Other effects could be toxicity which again may be dormant until there has been sufficient accumulation to make the effects noticeable.
This highlights what we do not know and so for those interested in a healthy future I would suggest that it would be wise to err on the side of caution and consider the air quality, not just during vacuum system cleaning but all day, everyday and down to a finer level than ever before.
1. Qinglin Hu, Xuan Bai, Guoqing Hu, and Yi Y. Zuo. ‘Unveiling the Molecular Structure of Pulmonary Surfactant Corona on Nanoparticles’ ACS Nano, 2017, 11 (7), pp 6832–6842 DOI: 10.1021/acsnano.7b01873
2. D. Docter, D. Westmeier, M. Markiewicz, S. Stolte, S. K. Knauer and R. H. Stauber. ‘The nanoparticle biomolecule corona: lessons learned – challenge accepted?’ Chem. Soc. Rev., 2015, 44, 6094--6121