In a recent study published in the journal Science of the Total Environment, researchers review the sources of airborne microplastics (AMPs), as well as their presence and dispersal in the atmosphere, physical and chemical properties, and toxic effects on the human respiratory tract.
Study: Airborne microplastics: A narrative review of potential effects on the human respiratory system. Image Credit: Trong Nguyen / Shutterstock.com
Since the original discovery of microscopic plastic fragments and fibers in marine habitats, researchers have also identified microplastics (MPs) in soil, sediments, water bodies, and biota. MPs can also be found in the most remote areas around the globe, including the poles, deep seas, and high mountains.
MPs pose a serious risk to ecosystems and human health, as demonstrated by several studies reporting the toxic effects of MPs on aquatic animals, primarily fish and small crustaceans. However, there remains a lack of data on the presence of MPs in the air and their adverse effects on human health.
Several studies have reported that the presence of MPs in humans is likely due to the ingestion of contaminated food or drinks. However, data on exposure to MPs through inhalation is scarce, and its toxic effects are less defined. Likewise, few studies have investigated the toxic effects of MPs on the human respiratory system using in vitro and in vivo models.
What are MPs?
MPs can be present in the form of beads, fragments, and fibers, with fragments and fibers most common. Previous studies have reported the smallest size of AMPs to be within the range of five to 100 micrometers (μm) in diameter.
This small size of some AMP particles prevents highly sensitive techniques like Fourier transform infrared (FTIR) and stereo microscopes with detection limits of 10-20 and 50μm, respectively, from being identified. Thus, there is a need for more advanced, sensitive, and high-throughput technologies for detecting MPs, including AMPs and nanoplastics (NPs).
Chemically, AMPs comprise repeated monomeric units of 20 or more types of polymers, polyethylene (PE) and polypropylene (PP). AMPs also consist of plastic additives, environmental pollutants, and pathogens.
Sources of AMPs
AMPs enter indoor environments and air through various sources. Synthetic textiles, for example, are considered the primary source of AMPs indoors.
Tire treads, household furniture, and waste disposal sites are other primary sources of AMPs. Previous studies have also indicated that smokers inhale more types of MPs, as cigarette filters are a potential source of tiny microfibers.
Human activities and meteorological conditions like wind speed often determine the deposition and atmospheric distribution of AMPs. For example, there is an increased abundance of AMPs in indoor areas where plastics are frequently used. Furthermore, AMPs are often present in higher amounts in areas with higher population densities.
Are AMPs toxic?
Previously, researchers determined the toxicity mechanisms of over 50 plastic additives. To this end, many of these additives were found to increase the risk of cancer, inflammation, and neurotoxicity; however, the health effects of most plastic additives remain unclear.
AMPs interact with cells in the human respiratory tract due to their unique physical properties, including size, shape, surface charge, and roughness. AMPs also interfere with cell membranes, which subsequently causes damage and oxidative stress.
Fibrous MPs are the most persistent type because of their shape, which prevents macrophages from successfully phagocytosing these particles. As a result, inhalation of fibrous MPs can lead to lung inflammation and respiratory lesions. Increased reactive oxygen species (ROS) production could also lead to programmed cell death or carcinogenesis.
The study findings highlight the urgent need for biomonitoring and toxicological assessment of smaller sizes, irregular shapes, and positively charged MPs in humans.
Given the widespread prevalence of indoor AMPs, particularly microfibers, young children and older adults who frequently stay at home are more vulnerable to being exposed to these particles. Thus, future studies are needed to elucidate the possible health effects of AMPs and establish effective approaches that can mitigate their toxicity.
Likewise, additional human studies assessing the occurrence of AMPs in the human respiratory system and the fate of AMPs in the human body are urgently needed. For example, studies using advanced detection methods could help discern whether MPs can penetrate the lung tissue barrier to reach the bloodstream.
Most commercially available AMPs are spherical and comprise known polymers; however, the real-world environment may also carry secondary MPs and source-specific AMPs. Thus, future studies are needed to better understand how exposure to these different types of MPs may have additive or synergistic toxic effects on human health.
- U. Vattanasit, J. Kongpran, & A. Ikeda. (2023). Airborne microplastics: A narrative review of potential effects on the human respiratory system. Science of the Total Environment. doi:10.1016/j.scitotenv.2023.166745