Microplastics: The latest air pollutant

By Tharosa M. Rajaratne
(Final year undergraduate)
and Prof O.A. Ileperuma, Emeritus
Professor, Faculty of Science, University of Peradeniya, Peradeniya, Sri Lanka

Air pollution is responsible for diseases, including respiratory infections, heart disease, stroke and lung cancer. There is increasing evidence which suggests that air pollution exposure may be associated with reduced IQ scores, impaired cognition, increased risk for psychiatric disorders such as depression and even baldness. The human health effects of poor air quality are far extensive and affect our respiratory and the cardiovascular systems. Reactions to air pollutants depend on the type of pollutant one is exposed to, the degree of exposure, and the individual’s health status and genetic composition.  Annual deaths due to air pollution is estimated by WHO at eight million and out of this 4.3 million deaths are due to indoor air pollution due primarily to firewood use in congested kitchens. Air pollution can be considered as the world’s largest single environmental health risk.  The extent of the air pollution crisis is enormous: 90% of the world’s population breathes unclean air to some degree and most governments are not concerned about this problem.

We are familiar with typical air pollutants such as carbon monoxide, sulphur dioxide and fine particles polluting the air we breathe. Now we have an additional air pollutant which we have to cope with and that is microplastics, a ubiquitous air pollutant present in our homes and outdoors and even in remote forests with serious health implications.

Microplastics (MPs) are plastic particles of microscopic dimensions (less than five millimeters). They comprise of particles of various shapes: fibres, fragments, and spheres, and often originate via fragmentation of larger plastic materials. Their role in aquatic systems has received a fair amount of attention in recent years. Scientists have found that they reach humans through the food chain particularly through the consumption of fish laden with microplastics in their flesh. Recently, microplastic fragments were discovered in human placentae, and also in human blood. The public awareness of microplastics is largely ocean centric as its pollution in aquatic systems is explicitly visible. Awareness regarding its presence in the air we breathe, however, is virtually nonexistent. This article intends to discuss the emergence of microplastics as the latest air pollutant.

A popular conviction until the turn of the millennium was that fibres are unbreathable, and hence cannot be found in human lungs. This was falsified by an experiment conducted in 1998, with the discovery of natural (cotton and wool) and synthetic (plastic) fibres being present in all regions of the human lung. It revealed that 99 of 114 tested human lung specimens contained fibres.

Nearly two decades later, around 2016, several studies conducted in the Greater Paris region made remarkable discoveries that detected microplastics in both outdoor and indoor air. Most of the detected particles were fibers, of which up to 50% were plastics such as polyester, nylon, rayon, etc. The results also indicated that indoors contain up to 60 fibres per cubic metre of air, 40 times greater than that found outdoors. It was estimated that the Greater Paris region (~2500 sq. km) could generate up to 10 tons of microscopic plastic fibers into the air annually.

In 2019, a research team discovered airborne microplastics in a remote, pristine mountain area, the French Pyrenees. It was revealed that about 400 particles got deposited over a square metre of land daily, containing plastic fibers such as polyester, polystyrene, and polypropylene. Most of the fibres measured were about 200 microns long, (a micron is a millionth of a metre) twice the width of a human hair. The important finding was that the particles seemed to have travelled for more than 90 kilometers in the atmosphere. These discoveries firmly establish the fact that microplastics have become the latest air pollutant, found everywhere from our homes to the pristine forest environments.

Most of the airborne microplastics are fibres, originate from the synthetic clothing we wear, soft toys and abrasion of plastic utensils and toys. Other sources include synthetic rubber, city dust, landfills, and burning of plastics, etc. Once liberated into the air from the parent material, microplastics disperse owing to their extremely small weight. Simultaneously, these particles are subjected to friction, abrasion, high temperatures, and sunlight, and further fragment into smaller pieces while altering their chemical makeup. With sufficient wind or rain, these particles eventually come down to earth. In the outdoor environment wind disperses the fibres and get diluted.

Microplastic concentrations indoors are significantly higher due to restricted ventilation causing shorter dispersion and higher accumulation. Also, a higher abundance of fibrous materials such as clothing, furniture, carpeting, etc., and their closer proximity to humans increases the risk of ingestion of these fibres into our bodies. A simple demonstration would be to witness larger fibrous particles released to air, by vigorously patting on an appropriate material such as a mattress or a cushion cover and shining a light beam at it.

Airborne microplastics can enter the human body via the mouth or nose. The size then governs the end destination within the respiratory system. Larger particles with sizes greater than 10 microns are removed through the intervention of hairs in the nose and the upper respiratory tract by coughing or sneezing. Smaller particles (<10 microns) reach the deeper lung tissues and are defined as respirable. The smaller particles get attached to the protective mucus layer of the alveoli of lungs causing its rupture through which other disease causing microorganisms can enter the lung and into blood circulation.

Most consumer plastics are bio-persistent i.e., resist biological degradation, and it is generally believed that microplastics in the lung may even outlive the host individual. Bio-persistence and their shapes are primary reasons why microplastic exposure is potentially toxic to humans.

Once microplastics are deposited onto the lung tissue, the body identifies them as foreign bodies and attempts to clear them by triggering inflammatory responses and various other defence mechanisms around the affected area. These reactions, however, are futile as microplastics do not break down. This causes persistent inflammation in the lung tissue that could lead to oxidative stress and eventually cellular damage. Prolonged cellular damage ultimately becomes the mediator that facilitates abnormal cell development such as cancer.

If a particle has the appropriate size and shape, it may even cross the membrane and enter the bloodstream. Such particles tend to create and develop blockages in the circulatory system. It must be noted that commercial plastics are treated with additional chemicals depending on their applications. Such additives and other contaminants can drastically increase the toxicity once inhaled. In addition, microplastics can adsorb various other toxic materials from the atmosphere such as polyaromatics given out during fuel combustion which is a well known carcinogen and also heavy metals all having adverse health effects.

Occupational (textile, PVC, etc.) exposure to airborne microplastics has been strongly linked to the prevalence of lung diseases. A flock (velvet/fleeced fabric) plant in Rhode Island USA, reported an unusually high incidence of interstitial lung disease among the workers during the late 1990s. Investigations revealed that lack of ventilation and the production method (cutting fibers) caused workers to inhale a significant amount of microplastic fibres during work. These fibres were often fully synthetic such as nylon and polyester. General exposure to fibres can often cause diseases such as asthma, wheezing, chronic pneumonia, chronic bronchitis, chronic obstructive pulmonary disease, etc. of which several are already showing rising trends in prevalence especially among school children in Sri Lanka.

Currently, there are no known solutions to mitigate this emerging disaster and it is evident that airborne microplastics have already become ubiquitous and permanent. Scientific understanding on airborne microplastics and their harmful effects is nascent but the adverse health effects is a matter of concern.