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Nanoparticles present a significant threat to human health across the globe. They contribute to air pollution and enter our lungs as we breathe and, over time, these particles can accumulate in our bodies and cause disease and death.
Recent research has linked exposure to nanoparticles to Alzheimer’s disease, cardiovascular disease (including heart disease and stroke), cancer, respiratory diseases (including asthma), and even psychological conditions such as autism, depression, anxiety and more.
While air pollution meters have become widely adopted by agencies across the world as a strategy of monitoring air pollution and collecting data to analyze in order to implement interventions to lower air pollution, these meters do not count nanoparticles. This is a major issue given the growing body of research that has linked exposure to nanoparticles in the air to serious illness and death.
To combat this serious threat to human health, scientists are working on developing analytical methods that can reliably and accurately measure nanoparticle pollution. Here, we discuss recent updates in this field.
The True Threat of Nanoparticle Pollution
Current warnings around the dangers of air pollution focus on the detrimental impact of exposure to particles known as PM2.5. These particles are roughly 30 times smaller than the width of a single human hair and measure around 2,500 nanometers. Much research has shown how PM2.5 particles threaten health and has given a sense of urgency to the need to prevent this kind of air pollution.
However, less is known about nanoparticles, particles that measure just 100 nanometers or less. We know less about the impact of nanoparticles due to the difficulty of tracking them because of their small size; however, what we do know is that, like PM2.5 particles, nanoparticles enter the body and infiltrate its organs - contributing to disease and premature death.
Evidence shows that while NOx gases are deemed to be the most dangerous to our health, only 14% of deaths attributed to air pollution are associated with exposure to NOx gases (such as nitrogen dioxide). This data demonstrates that nanoparticles may significantly contribute to illness and premature death from air pollution.
The Challenge of Measuring Nanoparticles
Back in 2017, scientists at the University of Edinburgh devised one of the first experiments to visualize how nanoparticles breathed in from the air impact the body. Previously, work had focussed on determining the nature of nanoparticle pollution, with previous studies revealing that up to 90% of all particles contaminating the air of busy roads are nano-sized.
With the knowledge that nanoparticle pollution is both excessive and detrimental to human health, the team in Scotland embarked on conducting an experiment that could demonstrate how nanoparticles behave once they are breathed into the lungs.
The team was presented with the challenge of devising a methodology that would visualize the nanoparticles in the body at a sufficient resolution. This was a difficult task, given the small size of the particles and the potential danger posed to the human subjects participating in the study.
The team decided to use gold nanoparticles to overcome the issue of causing harm to their participants as gold is known to be safe as it is inert and doesn’t react inside the body or cause oxidative stress. Additionally, gold is easy to detect, in comparison to carbon which can become disguised in the body amongst other carbon-based tissues.
Electrodes were used to create gold nanoparticles measuring as little as 2 nanometers. Next, the team used mice, getting them to breathe in the gold nanoparticles so they could then be traced within the body. Following this, the team ran the experiment on human participants. Samples of blood and urine were collected 15 minutes and 24 hours after inhaling the good nanoparticles.
The gold nanoparticles were visualized using high-resolution inductively coupled mass spectrometry and Raman microscopy. The results showed that the gold had passed through the lungs, into the blood and the urine. This was evident even three months later, showing how long exposure to nanoparticles can continue to impact the body.
When studying the mice, the team found that the nanoparticles had accumulated within the blood and liver, thus demonstrating, again, the ability of nanoparticles to pass through the lungs and translocate throughout the body.
On further examination, it was discovered that smaller nanoparticles were able to more easily move through the body, with translocation significantly higher for nanoparticles less than 10 nanometers in diameter. Overall, the team found 30 nanometers to be the cut-off point, with particles larger than that failing to move past the lungs.
The Future of Nanoparticle Analysis
Currently, there are a number of techniques that have successfully been used to measure the size and characteristics of nanoparticles, such as dynamic light scattering, disc centrifugation, nanoparticle tracking analysis, tunable resistive pulse sensing, atomic force microscopy, and electron microscopy. However, methods that track patterns of nanoparticle concentration and distribution in the air are less established.
Recent research has highlighted the ability of nanoparticles to translocate within the body once they enter the lungs. It is likely that this translocation is linked with the illnesses that have been linked with exposure to air pollution. There is an urgent need to develop analytical techniques to measure the level of nanoparticles in the air that are both scalable and cost-effective so that they can be widely adopted.
References and Further Reading
Bundschuh, M., Filser, J., Lüderwald, S., McKee, M., Metreveli, G., Schaumann, G., Schulz, R. and Wagner, S., 2018. Nanoparticles in the environment: where do we come from, where do we go to?. Environmental Sciences Europe, 30(1). https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5803285/
Miller, M., Raftis, J., Langrish, J., McLean, S., Samutrtai, P., Connell, S., Wilson, S., Vesey, A., Fokkens, P., Boere, A., Krystek, P., Campbell, C., Hadoke, P., Donaldson, K., Cassee, F., Newby, D., Duffin, R. and Mills, N., 2017. Inhaled Nanoparticles Accumulate at Sites of Vascular Disease. ACS Nano, 11(5), pp.4542-4552. https://pubs.acs.org/doi/10.1021/acsnano.6b08551
Raftis, J. and Miller, M., 2019. Nanoparticle translocation and multi-organ toxicity: A particularly small problem. Nano Today, 26, pp.8-12. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6558960/