What are the Health Effects of Ultrafine Particles?

Ultrafine particles (UFPs) are ubiquitous – they are present in air everywhere. They come from many sources , including many human activities (transportation, cooking, etc.) and also many natural environmental processes. Given how common they are, it would be easy to presume that they could not possibly have negative impacts on human health.

As is often the case, though, something that was long presumed to be nearly innocuous is slowly revealed to have deleterious effects on human health. This process has happened for many environmental pollutants in the past (e.g. lead, PM10, PM2.5, etc.), and a steadily growing body of research is elucidating the health impacts of UFPs. The picture is emerging that UFPs pose a unique health hazard, and that monitoring them should be considered as a means to address growing health concerns related to particulate air pollution

Health Effects of Particulates in Ambient Air

Poor health effects of breathing outdoor air pollution are not only the result of inhaling harmful gases, but also breathing in tiny particles that float in ambient air and nestle deep within the lungs. A significant amount of research has been done in the area of health effects of exposure to airborne particulate matter (PM) of 2.5 micrometer in size or less (PM2.5).

It has been well-established that ambient PM2.5 exposure is associated with respiratory illnesses, such as chronic bronchitis and pneumonia, and cardiovascular diseases, such as congestive heart failure and coronary heart disease.^1,2 And PM2.5 is an important pollutant to monitor as over 90 % of the monetized social costs of particulate air pollution are due to particles 2.5 micrometers and smaller.³ 

Since UFPs are smaller than 2.5 micrometers, technically they are included in the PM2.5 metric. Given their tiny size, however, they have an extremely low mass. As such, it’s entirely possible to have a very large population of ultrafine particles present, but for the PM2.5 mass measurement to barely respond to that presence.

Because of this, studies that look at health effects as a function of PM2.5 exposure are very likely not able to pinpoint the health effects exerted specifically by the ultrafine particles. Despite this challenge, studies carefully designed to examine UFP exposure continue to build the case that ultrafine particles pose a greater health hazard than previously assumed.

Health Effects of Ultrafine Particles

As stated above, UFP’s are considered to be 0.1 microns in size or smaller; particles in this size range can also be referred to as “nanoparticles.” The smallest UFPs are only 5-10 atoms across. Because UFPs are so small, they behave differently within the respiratory system than do larger particles. One key attribute of UFPs is their ability to cross the blood-brain barrier.⁴

Because of UFPs’ ability to translocate within the body, some researchers have utilized this ability to demonstrate the consequences of exposure to UFPs. In a 2020 study published in Nature Communications, nanoparticles that formed outside the human body were found in human lung fluid.⁵ The exposure to particulate air pollution in the examined cases was unintentional, as individuals were simply carrying out their routine activities and had encountered these particles in the surrounding air. As a result of this exposure, the particles were absorbed and accumulated in their lung fluid.

In a separate study, volunteers were exposed to the hazard of breathing in inhalable particles in the form of aerosolized gold nanoparticles of sizes 5 and 30 nm. The particles were detected in the volunteers’ blood and urine within 24 hours, and were still present after 3 months.⁶ This research suggests that UFPs can easily enter the body and remain there for extended periods of time, potentially causing long-term health effects.

Other research work has focused on understanding the pathways between PM0.1 exposure and health consequences. Disease development occurs via oxidative stress, epigenetic changes, and other mechanistic pathways, all of which can be initiated by exposure to PM 0.1, i.e. ultrafine particles. Oxidative stress, for example, can cause inflammation and damage to cells, leading to a variety of health problems such as cardiovascular disease and cancer. Epigenetic changes, on the other hand, can alter the way genes are expressed, leading to changes in cell behavior and the development of disease.⁷

Monitoring of Ultrafine Particles as a Means to Address Growing Health Concerns

The scientific understanding that UFPs pose a unique health hazard is growing ever stronger. Since the very motivation for ambient air quality monitoring is protecting public health, adding UFP measurements to regular ambient air monitoring efforts would help identify areas where UFP occur at high concentrations and initiate changes to protect health. Such efforts are already underway in the ACTRIS network and other research efforts. Standardizing the measurement techniques of UFPs – which will strengthen epidemiological studies as to the effects of UFPs – is well underway thanks to two European technical specifications, EN 16976* and CEN/TS 17434.

*EN 16976 is formerly known as the Technical Specification CEN/TS 16976, and established by the European Committee for Standardization (CEN).