Every day, we inhale and exhale without a second thought. Why? Because we believe we breathe fresh air. The fresh air we hope to breathe consists of a mixture of simple gases, mainly oxygen and nitrogen. However, this air can be polluted with very different tiny particles emitted from natural sources and human (anthropogenic) activities in our day-to-day life, which might be harmful to our health. These tiny particles are known as nanoparticles. This blog post explains how nanoparticles are released in our environment, their sources, how they end up in the air we breathe, the nanoparticle cocktail in urban and rural areas, and their potentially harmful effects on humans and the environment.
More than just air
In today’s world, every breath we take contains a complex mixture of suspended particles from various sources, both natural and human-made, according to the UN Development Programme (UNDP). Alongside oxygen and nitrogen, the atmosphere holds dust, pollen and tiny fragments from various sources. These ultrafine particles remain airborne from a few hours to several months, infiltrating indoor spaces and traveling hundreds of kilometers, to the extent that almost every inhalation introduces far more than just simple gases into our lungs. According to the World Health Organization, 99% of the world’s population breathe polluted air, and nanoparticles carry a significant portion of polluted air as they are ubiquitous in the atmosphere.
What are Nanoparticles?
Nanoparticles are extremely small particles of particulate matter that measure between 1 and 100 nanometers in size. For comparison, they are about 50,000 times smaller than the diameter of a single human hair strand. These particles are pollutants released into the environment through various natural and human-made sources. They are generally categorized into two groups: those intentionally produced for specific uses, called Engineered Nanoparticles (ENPs), and those that are naturally occurring or produced as byproducts of human activities like combustion or plastic degradation, known as non-engineered nanoparticles (NENPs). Nanoparticles are airborne, meaning they are primarily found in the air and can also settle on water surfaces. They consist of thousands of different types of particles, including metals such as iron oxides, black carbon (soot), microplastics, nanoplastics, or complex mixtures. Their tiny size allows them to clump together or stick to larger particles, forming particulate matter.
Urban sources of nanoparticle emission
The composition of the nanoparticles in the air differs primarily with the geographical location. In cities and developed areas, nanoparticles may be composed of fragments from industrial emissions (e.g., steel plants, refineries, mining and chemical factories), incinerators (waste‐to‐energy plants), and via the breakdown of used plastics as well as synthetic clothing fibres. Traffic is another major contributor to nanoparticles in the cities. The combustion engines emit ultrafine soot and metal oxides, while tire abrasion and brake‐pad wear may also release microplastic fragments and metallic dust to the urban nanoplastics cocktail. Construction sites also release a huge amount of particulates into the atmosphere, which alone contribute about 30% of particulate matter in the air according to the 2019 London Atmospheric Emissions Inventory (LAEI). These include cement, silica, and paint particles, and other building materials that produce nanoparticle debris laden with toxic metals. Nanoparticles from urban houses may also seep outdoors, as cooking and heating appliances may emit carbonaceous particles (particles composed primarily of carbon).
Rural sources of nanoparticle emission
It is generally believed that the air quality in rural and undeveloped areas is better than the cities. This can be untrue because even with the relatively fewer industrial activities compared to the urban areas, the air quality may be worse; it is just composed of a different cocktail of nanoparticle pollutants. As a matter of fact, a recent 2022 study found that pollution particles in rural areas are can be just as harmful. Nanoparticles in rural areas are emitted from particles of fertilizers and pesticides used during agricultural activities. These chemical substances can become volatilized or aerosolized (suspension of solid or liquid droplets in air) during spraying. Other rural sources of nanoparticles include pollen, dust from unpaved roads, microplastics from sheet abrasion, and smoke from wood-burning stoves or agricultural fires, which become suspended in the air for a long time.
NP transport and environmental impacts
Nanoparticles know no boundaries; they are susceptible to long-range transport due to their ability to float in the air. This enables urban or rural areas to have a cocktail of particles that are not necessarily produced in the area. For instance, urban smog particulates may travel to rural areas, while microscopic dust particles from farms can blow into cities. They can also be transported from aquatic to terrestrial ecosystems. Ecologically, these particles disrupt plant photosynthesis, inhibit soil‐invertebrate reproduction, and bioaccumulate in aquatic organisms, thus undermining ecosystem services and food quality.
The societal burden: health impacts of NPs
Nanoparticle pollution, often called “nano-pollution,” is considered a serious human and environmental threat due to its unique characteristics and ubiquitousness. Due to its very small size, they can easily penetrate animal cells and cause serious harmful effects. When inhaled, they can penetrate deep into the lung’s alveoli, triggering inflammation, oxidative stress, and even translocation into the bloodstream, where they can cause cardiovascular and neurological disorders. Aside from inhalation, humans can be exposed to nanoparticle pollutants via oral ingestion of drinking water, aquatic organisms, or food crops in agricultural lands, as nanoparticles settle on these media.
Dermal exposure is another exposure route to nanoparticles, and this occurs when settled nanoparticles are re‑suspended by wind or human activity and come into contact with our skin. Ingestion of deposited nanoparticles via contaminated drinking water or food has been linked to gut dysbiosis, mucosal damage, and systemic organ toxicity, while dermal contact through soil, dust, or personal‐care products allows certain nanoparticles to breach the skin barrier and cause localized cytotoxicity and even serve as vectors for deeper tissue uptake of nanoparticles.
Our shared responsibility for clean air
Nanoparticles are increasingly recognized as emerging stressors that pose potential risks to both human health and the environment. Therefore, achieving truly clean air that is free from nanoparticles requires a collective action. Air monitoring is important. Each locality must routinely report its Air Quality Index (AQI) values using the PM2.5 concentrations, to quickly detect when it exceeds the 5 µg/m³ annual or 15 µg/m³ 24-hr PM2.5 average concentration limit set by the WHO. Controlling particle emissions from the source is another measure. This could include, amongst other measures, upgrading vehicle fleets, enforcing industrial emission limits, and reducing open‑burning. Indoor air management, e.g., with the use of air purifiers, could also help reduce human exposure, as well as supporting advocacies for green‑space expansion, policies that reduce particulate emissions, and the adoption of low-emission commuting, such as cycling and electric vehicles. By combining these measures, we can collectively turn the tide on nano-pollution and ensure we breathe cleaner, healthier air.
Author: Adetola Adebowale