I really sat up and took notice of ultrafine particles when I realized they could get straight into my blood stream and settle in my brain! I thought that cannot be good, and so I decided to look into ultrafine particles further.
More than 90% of airborne particles in cities are ultrafine that is, less than 0.1 um in diameter. So the most commonly researched particles, PM2.5, whose levels are reported countrywide are only 10% of the particles in the air! To be fair though, there is good data linking PM2.5 to poorer health outcomes. But what are the health implications of the other 90% of particles the ultrafine particles?
On the whole ultrafine particles cause an increase in cardiovascular events, such as heart attacks and strokes, respiratory problems and increase mortality. They enter our blood stream and our brains and adversely affect the health of children. They may even cause us to age faster.
Particulate air pollution is the major determinant of air quality except for some localized areas of the U.S. where there is a concentration of chemical plants such as “cancer alley” along the Mississippi. Particulate air pollution is the 15th most important risk factor for death in the U.S. and leads to 930,000 years of life lost each year in the US.
The toxic effect of ultrafine particles increases as their particle size decreases. This is partly because smaller particles have a larger surface area so more toxins become attached to their surface.
It is also partly that they can penetrate tissue easily because of their size and so enter our bloodstreams. They simply diffuse across the cell membrane into the cells lining the air sacs, “alveoli”, and then diffuse across the membrane on the other side of the cell and enter the bloodstream. Once in the bloodstream they can enter any cell in the body, as well as diffusing into the nucleus of a cell.
- Ultrafine particles-particles with a diameter of less than 0.01 um
- PM2.5-particulate matter made of particles with a diameter of less than 2.5 micrometers
- PM10-particulate matter made of particles with a diameter of less than 10 micrometers
What Causes Ultrafine Particles
Natural causes
- smoke
- ocean spray
- (volcanic eruptions)
- Biological ultrafine particles come from bacteria. Either lipopolysaccharide from the bacterial cell wall or extracellular vesicles. Lipopolysaccharide fragments cause inflammation in the airways and is associated with asthma, chronic obstructive airways disease and lung cancer. Extracellular vesicles are also associated with asthma, chronic obstructive airways disease, and lung cancer.
- Viruses can be small enough to fit the size criteria for being an ultrafine particle
Please note that forest fires apart from producing profound chemical pollution of the atmosphere also produce a considerable amount of ultrafine particle pollution.
Human sources
- Ultrafine particles are caused by combustion of fossil fuels, wood and tobacco. In cities with lots of traffic about 50% of ultrafine particles are particle emissions from vehicles with internal combustion engines. However, in cities with less traffic only 25% is from vehicles, so other sources can be important.
- A substantial portion of ultrafine particles come from brake dust.
- Laser printers and photocopiers-present in the toners.
- Cooking causes the production of ultrafine particles.
- Peeling citrus fruit
- Vacuuming creates copper and carbon ultrafine particles which come from the vacuum’s motors as the motor turns. It also distributes existing ultrafine particles into the air which is sucked into the vacuum. However, not all vacuum filters will capture them. To minimize this use a vacuum cleaner with a HEPA filter which will capture ultrafine particles efficiently.
So human activity can increase ambient ultrafine particles in indoor air. In an era with increasingly sealed homes because of climate change air pollutant in the indoor air can become more concentrated. This can mean that the indoor air is worse than the outdoor air.
Ultrafine particles are either made of carbon-based molecules such as smoke or metal based particles such as particles from electric motors.
Numbers of Ultrafine Particles
It will probably surprise you to learn that the air that you are now breathing has more than 2 million ultrafine particles per litre (1.76 pints)! So as a normal volume of respiration (breathing) per minute is at least 5 litres we are all breathing in at least10 million ultrafine particles per minute.
A 2021 study has shown that in the US the mean number of ultrafine particles in the air people are breathing is 6.5 million per litre, so people are on average breathing in 32.5 million particles per minute. This study also showed that the exposure in cities was 3 times that of rural exposure.
However the range of the difference in exposure can be almost 20 fold depending on where in the city you live-
- Rural Areas 2610 particles/cm3
- Roadside 48,180 particles/cm3
The roadside particle count falls back to normal with distance so that at 500 m from the road it is down to background levels. We know that dementia rates are 40% higher near roads.
The concentrations of ultrafine particles in the air in winter are approximately double the concentration in the summer.
How do Ultrafine Particles Get Into and Out of the Body
Ultrafine particles are breathed in and can reach the deepest parts of the lungs the alveoli. From here they can enter the bloodstream and reach any organ in the body. One study found nanoparticles in the serum and bodily fluids in this study pleural effusions (fluid around the lung). On analysis of these nanoparticles it was found that they were from combustion derived particulate emission, that is vehicles.
They can enter our brains directly by entering the olfactory nerve in our noses and then travelling down it directly into the brain.
They are removed from our body’s by being filtered out of the bloodstream by the kidneys and then leaving the body in the urine.
Effects of Exposure to Ultrafine particles
The Unborn Child
In a study of 160,641 expectant mothers during pregnancy, exposure to ultrafine particles during the second trimester was associated with an increase in likelihood of asthma in her child of up to 20%. Pregnant women when exposed to ultrafine particles had an increased risk giving birth to a child of low weight especially if they lived within 50 m of a busy road.
Children
In children 8-11 years old inhalation of ultrafine particles made no difference to lung function but raised a marker of inflammation in the body. This is consistent with ultrafine particles penetrating deep into the body to cause inflammation.
Conversely, a review of studies concerning ultrafine particles and children’s health found that these particles did affect health. This was particularly for respiratory illness, when ultrafine particle exposure increased inflammatory markers and reduced lung function. They also remarked that the health effects for ultrafine particles were related to their ability to penetrate into tissues because of their small size.
Having a smoking adult in the home, burning things in the home such as candles and being in the kitchen when cooking is ongoing exposes children to the highest levels of ultrafine particles.
However although we know that children are very vulnerable to particulate pollution because their organs are still developing more research needs to be done to tease out the contribution of fine (PM2.5) and ultrafine particles. Please see this article “The 13 problems from air pollution“.
From a practical point of view however a true HEPA air purifier specified to remove the smallest possible ultrafine particles will deal with both.
Adults
Short-term exposure-effects mainly on the heart and circulation
Heart and Circulation
In a study near an airport on healthy subjects, ultrafine particles affected the heart, circulation and lungs. Particles less than 20nm in diameter changed the heart’s electrical activity by prolonging the time it takes to repolarize and prolonged the QTc interval on the EKG. An increase in the QTc interval has been associated with a fatal cardiac arrhythmias. These particles also reduced the volume of air that can be forced out of the lungs-FVC (force vital capacity). Ultrafine particles 50-100nm in diameter were associated with an increase in blood pressure.
Respiratory System/Lungs
Ultrafine particle exposure is associated with cough decreased airway function and an increase in hospital admissions for asthmatics.
In another study, respiratory symptoms in elderly subjects with coronary artery disease exposed to particle pollution were more correlated with PM2.5 particles than with ultrafine particles.
Clinical studies in which subjects breathed in air with ultrafine particles showed some interesting results. There was little effect on respiratory function, however inflammatory markers on white cells were altered and flow mediated dilation of arterioles (very small arteries) was reduced.
Brain
Much of the information that has been derived from animal studies suggests that ultrafine particles have access to the brain and heart in addition to respiratory systems. In experiments ultrafine particles can be found in the brain 4-24 hours after inhalation. They have direct access to the brain via the olfactory nerve the nerve in the nose that allows us to smell. Once they enter this nerve, they can travel up it directly into the brain, bypassing the blood-brain barrier.
In animal experiment ultrafine particles impair short term memory. Ultrafine particles also affect emotional behaviour, learning capacity and spontaneous motor activity.
Brain derived neuotrophic growth factor(BDNF), is “fertilizer for the brain”, and we produce it in increased amounts when we exercise. In one study when cycling in an air-filtered room BDNF rose but not after cycling near a major traffic route where ultrafine particle levels are very high.
Brain cancer seems to be linked to ultrafine particles. Ultrafine particles were found in brains in 2016. A study from Canada covering 1.9 million people has linked air pollution to the incidence of brain tumors. There was a link between ultrafine particle exposure and brain tumors. PM 2.5 and nitrogen dioxide exposure were not linked to brain tumors.
Generalized Inflammation in the Body
A systematic review of the literature concerning ultrafine particles and human health was published in 2019. This reviewed 85 original studies and concluded that there were adverse short-term changes in the cardiovascular (heart and arteries) system and inflammatory changes. These effects may be independent of other pollutants, that is a particular effect of ultrafine particles.
Long-term ie chronic ultrafine particle exposure-increases heart attacks, heart failure and mortality
Heart Attacks and High Blood Pressure
Long-term exposure to ultrafine particles was found to be associated with an increase in heart attacks and heart failure. This was not seen for PM2.5, so measurement of PM2.5 as currently widely practiced may underestimate the effect of air pollution. This study did find an increase in NO2 was linked to an increase in heart failure and coarse particulate matter levels to an increase in cardiovascular events in general. There were similar findings in another study which linked ultrafine particle exposure to an increase in heart attacks and heart failure.
A further study found that ultrafine particles were associated with developing high blood pressure and diabetes. Also, this association remained despite adjusting for NO2 and PM2.5. Similarly a study from Taiwan found an increase in blood pressure and systemic inflammation with long-term exposure to ultrafine particles. Conversely, another study did not find that ultrafine particles cause an increase in blood pressure.
Exposure to traffic related ultrafine particles was found to affect inflammation, endothelial function and mitochondrial bioenergetics forming reactive oxygen species. These changes can make the lining of blood vessel, the endothelium, function less well leading to heart attacks.
Cancer
An association between ultrafine particles and brain cancer has been reported. Studies in animals and human cells have shown that ultrafine particles cause or can carry substances which cause mutations and stimulate tumour formation.
Respiratory Disease
In another longitudinal study ultrafine particles were associated with the development of chronic obstructive pulmonary disease but not asthma or lung cancer. However when correcting for nitrogen dioxide levels, there was no longer a significant relationship, so it seems that nitrogen dioxide levels are a more important factor. Another group showed that ultrafine particles cause airways in the lungs to become inflamed and that this exacerbates asthma, bronchitis and chronic obstructive pulmonary disease.
By studying the time course of ultrafine particle and fine particle concentrations if became apparent that ultrafine particles had more effect on respiratory function than did fine particles(PM2.5).
In experimental studies, there is a phenomenon of “overload” of the lungs. In this, as the concentration of inhaled particles increases, there comes a point at which inflammation, fibrosis and tumour formation occur. This is most closely related to the surface area of the particles, and of course, ultrafine particles have a very large surface area, much larger than PM2.5 or PM10 per unit of weight.
All Cause Mortality
A study of the bay area of San Francisco showed that there was and excess cardiovascular, respiratory and all cause mortality. It also showed that respiratory hospitalizations increased 20% for a moderate increase in ultrafine particles.
So it seems that ultrafine particles increase heart attacks, heart failure and mortality. Ultrafine particles probably also adversely effect lung function in the short term.
Ultrafine Particles- Do They Speed up Aging?
Ultrafine Particles Have Access to All Tissues in Our Body
Ultrafine particles are those less than 100 nm. They’re found in smog, soot, smoke, some viruses, atmospheric dust, and gases. In open areas they are mainly formed by combustion. Not only is the size important the surface chemistry, charge and composition are also important. Ultrafine particles are small enough to enter the deepest parts of the lung, the alveoli. This is where the air enters the bloodstream, these fine particles can also enter the bloodstream just as molecules of oxygen can. From here they can affect all the blood vessels in the body and even penetrate into the organs such as the brain and heart.
They can directly cross cell membranes into the interior of cells! Here they have direct access to the machinery of the cell including the nucleus.
Nanoparticles formed from presumed brake dust have been found in the brains of people. Also, nanoparticles of carbon from air pollution been found in children’s urine. So they have entered the child through the lungs traveled around the body in the bloodstream and finally been filtered out of the blood by the kidneys.
An interesting study in which volunteers inhaled gold nanoparticles showed the ease with which nanoparticles enter the bloodstream. Gold was detected in the blood in urine within 15 minutes to 24 hours after exposure and even 3 months after exposure was still present. 5 nm particles were found in greater concentration in the body compared to 30 nm particles. Studies in mice showed that Nano particles accumulated following pulmonary exposure in both blood and liver. Again, the accumulation was greater for particles less than 10 nm in diameter.
The particles preferentially accumulated in inflamed vascular lesions in arteries. These lesions tend to be more unstable, with a greater tendency to lead to heart attacks and strokes. Also, following inhalation in patients, gold particles were detected following carotid surgery in tissue removed from the carotid artery wall. This would provide a direct mechanism by which ultrafine particles could destabilize arterial walls and lead to the increased incidence of heart attacks and strokes that are seen with increased air pollution.
It is the sheer number of ultrafine particles that manage to penetrate our body’s defences and enter the body that leads to a greater effect on internal organs than larger particles-
Larger particles exert their effect on the internal organs indirectly. They cause inflammation in the lungs and the inflammatory proteins then travel in the bloodstream to have an effect on the internal organs.
In addition to adverse health effects. Ultrafine particles can affect cellular processes known to be associated with aging.
Numerous toxicological effects of fine particles have been found –
- Impairment phagocytosis (ability of white cells to eat bacteria etc.)
- Crossing tissues and cell membranes
- oxidative stress
- Inflammation
- mitochondrial (the powerhouses of the cells) exhaustion
- damage to protein
- damage to DNA
Inflammation in the body is known to be linked to aging. It has recently become apparent that the stimulation of Aryl hydrocarbon receptors (AhR) by air pollution leads to increase production of interleukin 33, which stimulates inflammation. These receptors are found on cells in organs that are in contact with air – the skin, the gut and lungs. The inflammation can exacerbate asthma could also potentially lead to accelerated aging.
A study before, during, and after the Beijing Olympics looked at air pollution. It found a change in 69 metabolites in the blood. Some of these changes would due to the breakdown of cells release of membrane components into the bloodstream. These can then turn into molecules that stimulate inflammation. The scientists also found an increase in antioxidants thought to be part of our body’s defense mechanism. They found an increase in oxidative stress, inflammation, mitochondrial exhaustion, damaged protein, and damage to DNA, all mechanisms of aging. So, in effect, exposure to airborne particles may accelerate aging.
Aging/Age-Related Declines in Health Are Increased by Particulate Air Pollution
Those people exposed to more traffic related air pollution experience 3 years more decline in health status and those exposed to less. So traffic related applications seen as accelerating the usual age-related decline in health.
Telomeres shorten as we age, and so shorter telomeres are taken as a sign of increased aging. Babies born to mothers you are exposed to air pollution have 9% shorter telomeres in their blood cells. They also have 16% shorter telomeres from cells in their placenta. Preschool children who live near roads or have more roads near their houses have shorter telomeres. Traffic related pollution was also associated with shortened telomeres in children and adolescents in California. Similarly, in adults long-term exposure to small particles (PM 2.5) was linked to shorter telomeres.
Shortened telomeres have been linked to a shorter lifespan, bone marrow failure, pulmonary fibrosis and liver disease.
Also, the EPA regard air pollution as a factor in lung aging-please see EPA infographic (1st illustration above).
As mentioned above, particles in the air induce oxidative stress in skin. They also promote external signs of skin aging. Ozone at levels found in urban areas decreases sirtuin 3 activity in epidermal skin cells. Sirtuins are involved in the cellular biology of aging, with sirtuin 3 located in the mitochondria – the main powerhouses of our cells. So by inhibiting sirtuin’s ozone can be thought of as increasing the rate of aging. Another study also found that skin aging is increased by exposure to traffic related air pollution.
So, there is scientific evidence that air pollution influences at least 3 cellular mechanisms of aging. Also, for skin more exposure to air pollution leads to the appearance of more aged skin.
Premature Death is Linked to Particulate Air Pollution
There is evidence of a link between fine particle air pollution and premature death, even at particle counts below the current EPA standard of 12ug/m3. A study of 6 US cities found that particulate air pollution was linked to death, particularly from lung cancer and cardiopulmonary causes. Following the Clean Air Acts, a decrease in mortality has been seen. It has been calculated that for each 10 mcg/m³ decrease in PM 2.5 pollution, people live in an additional 0.6 years. In another study of 500,000 Americans, followed over 9 years, it was found that mortality increased 3% per 10 mcg/m³ of PM 2.5 exposure.
Interestingly, although total mortality increased 3%, cardiovascular mortality increased 10% but the increase in mortality from respiratory disease was not significant. This is surprising and implies that the particles entering the bloodstream are more lethal than those simply deposited in the lungs.
A study of 1/2 million people from the UK biobank study used two normal statistical methods as well as a machine learning algorithm to predict mortality. The machine learning algorithm turned out to be better at predicting mortality than either of the conventional statistical methods. It’s 9th most important variable in making the prediction was air pollution.
Air pollution in the United States causes 100,000 deaths per year. Half of these deaths are from PM 2.5 generated particles from electricity generation and cars. However, woodstoves and livestock are also a big problem. For instance, ammonia generation by livestock from manure can cause formation of PM 2.5 particles in the atmosphere and these are responsible for 20,000 deaths per year in the US. In the US it is estimated that national life expectancy is decreased by about 2 months because of air pollution.
Another study in 2021 from Harvard found that mortality from particle pollution had been underestimated. It found a particular problem in the China and India but also in the eastern United States, anywhere where large amounts of fossil fuel are burned. Particulate pollution contributed to 17% of deaths in the UK and 13% of deaths in the US.
In the EU in 2015, it is estimated that 659,000 deaths were caused by air pollution. This reduced life expectancy by 2.2 years. It is estimated that China could increase life expectancy by almost 3 years by meeting WHO standards for air pollution. Worldwide it is estimated that 8.8 million deaths are caused each year-more than smoking, which causes 7.2 million deaths!
So which types of particles are particularly problematic? One study looked at the metal particulate matter present in samples of moss and then correlated this with mortality. The participants exposed to higher atmospheric concentrations of metals due to human activity had a higher mortality. So metal particles may be especially problematic.
It seems even premature death is one of the health problems from air pollution.
Occupations With Particularly High Exposure to Ultrafine Particles
In some occupations ultrafine particle concentrations can be 60-450 times higher than the background concentration.
- Welding-levels of exposure to ultrafine particles can be 100 times that of a general urban neighbourhood.
- Machine shops
- Traffic related occupations
- Restaurants-(and kitchens at home!-please see this article “Best air purifier for a kitchen“)
How to Reduce Exposure to Ultrafine Particles
The best way to limit exposure to ultrafine particles is to buy air purifiers that are certified to reduce ultrafine particles.
| Air Purifier | Minimum Particle Size Specified to Remove (nm) |
|---|---|
| iQair HealthPro Plus | 3 |
| Coway 400S | 10 |
| Coway 300S | 10 |
| Coway AP1512 HSS | 10 |
| Oransi EJ120 | 20 |
There is an extensive review of the iQair HealthPro Plus in this article. There is also an article which outlines the Coway 400S and 300S here.
If you cannot afford one of these air purifiers certified to remove ultrafine particles do not worry too much as true HEPA filters are generally good at removing ultrafine particles.
Whichever air purifier you buy be very careful that it has a clean air delivery rate that is enough for your room at a noise level that you can tolerate. This is more difficult than it sounds as many manufacturers do not give the noise level for each fan speed. For very useful information about buying an air purifier please consider reading this article and for the highest flow quietest air purifiers this article.
Always have the fan speed as high as you can reasonably tolerate, this will ensure your lowest possible exposure.
When cooking use a hood over the cooking area with an extractor fan. Ideally cook with electricity rather than gas. Also steam food rather than fry, grill or bake it.
Traveling on the subway will expose you to less than half the ultrafine particle concentrations that you will receive in a car in a city and a quarter of the amount of that you would receive on a motorbike. The reverse is true for PM10 which is much higher on a subway.
Can I Buy a Meter to Measure My Ultrafine Particle Count?
The most practical meter for measuring ultrafine particle count is the P-Trak 8525, this is quite easy to use and works well. Please see video below-
It will measure particle size from 20-100nm. The problem is that new it costs about $4000. You may be able to pick up a used one for around $500-1500 but it would then need calibrating and servicing by TSI which is likely to cost around $400.
Should Ultrafine Particle Exposure be Regulated?
Yes it should because of the health effects. Ideally there should be agreement first on the methods used for measuring ultrafine particles so that all measurements are standardized.
Conclusion
Ultrafine particle air pollution is a considerable concern especially as it is linked to cardiovascular disease such as heart attacks, respiratory illness to some extent and increased mortality. It also concerned me that ultrafine particles have been found in the brain and that air pollution is linked to dementia. Damage to the brain cells, “neurones” is a particular problem as the neurones in the brain have to last a lifetime. They cannot be replaced in large numbers, otherwise the neural connections that we have built up over a lifetime would be lost and we would lose our memories and personality.
Fortunately there are excellent air purifiers specified to remove ultrafine particulate matter as listed above.
One last thought. We are going to see many anti-aging medicines reach the clinic over the next few decades these will be able to tackle DNA, RNA, proteins, autophagy, cellular senescence, inflammation….. but will they be able to help a brain riddled with ultrafine particles?
Possibly the best approach is to limit our exposure to ultrafine particles.
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