In a recent study published within the journal Science of the Total Environment, researchers review the sources of airborne microplastics (AMPs), in addition to their presence and dispersal within 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

Background

Because 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 may also be present in essentially the most distant areas across 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. Nonetheless, there stays a scarcity of information on the presence of MPs within the air and their antagonistic effects on human health.

Several studies have reported that the presence of MPs in humans is probably going on account of the ingestion of contaminated food or drinks. Nonetheless, 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 could be present in the shape of beads, fragments, and fibers, with fragments and fibers commonest. Previous studies have reported the smallest size of AMPs to be throughout the range of 5 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 may be a necessity 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 kinds 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 instance, are considered the first 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 kinds of MPs, as cigarette filters are a possible source of tiny microfibers.

Human activities and meteorological conditions like wind speed often determine the deposition and atmospheric distribution of AMPs. For instance, there may be an increased abundance of AMPs in indoor areas where plastics are continuously used. Moreover, AMPs are sometimes 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, a lot of these additives were found to extend the danger of cancer, inflammation, and neurotoxicity; nevertheless, the health effects of most moldable additives remain unclear.

AMPs interact with cells within the human respiratory tract on account of 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 essentially the most persistent type due to their shape, which prevents macrophages from successfully phagocytosing these particles. In consequence, inhalation of fibrous MPs can result in lung inflammation and respiratory lesions. Increased reactive oxygen species (ROS) production could also result in programmed cell death or carcinogenesis.

Conclusions

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 continuously stay at home are more vulnerable to being exposed to those particles. Thus, future studies are needed to elucidate the possible health effects of AMPs and establish effective approaches that may mitigate their toxicity.

Likewise, additional human studies assessing the occurrence of AMPs within the human respiratory system and the fate of AMPs within the human body are urgently needed. For instance, studies using advanced detection methods could help discern whether MPs can penetrate the lung tissue barrier to succeed in the bloodstream.

Most commercially available AMPs are spherical and comprise known polymers; nevertheless, the real-world environment can also carry secondary MPs and source-specific AMPs. Thus, future studies are needed to raised understand how exposure to those various kinds of MPs could have additive or synergistic toxic effects on human health.