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South à£à£Ö±²¥Ðã State University researchers are critically examining published research on microplastics to better understand this emerging problem. 

Each hour, a person will inhale up to 16 plastic fragments from their clothes or the environment. Over the course of the week, that equates to a lot of plastic, roughly an entire credit card's worth. These findings, from a study conducted by Danish researchers, are concerning.

The problem is microplastics, microscopic fragments of plastic from everyday items that are circulating in our environment. Microplastics — particularly airborne microplastics — are emerging as one of the most concerning topics in all of science.

To better understand the impact microplastics and airborne microplastics are having on human health, South à£à£Ö±²¥Ðã State University researchers have conducted a critical review of over 200 published research studies from around the world.

"Tiny plastic particles, known as airborne microplastics, are floating in the air we breathe, indoors and outdoors," said Pradeep Kumar, graduate research assistant in SDSU's Department of Agricultural and Biosystems Engineering. "Our study highlights how these invisible plastics can enter the human body and potentially harm our lungs, immune system and overall health."

The study, titled was published in the Journal of Environmental Sciences.

Where do they come from?

Plastic is all around us. It's used in every sector of society. But the problem with plastic is that it takes hundreds of years to fully biodegrade in the environment. As this process occurs, plastic breaks down into tiny pieces — smaller than a grain of sand — referred to by scientists as microplastics and nanoplastics, depending on the size of the fragment. Synthetic fabrics are one of the primary sources of airborne microplastics, the researchers noted.

Microplastics have found their way into every corner of the globe. Scientists have even found microplastics in the most remote areas on Earth, like Artic snow. They have also made their way into water bottles, produce and the human body.

"We urge more research and awareness, as these pollutants are becoming a growing threat to public health," said Yizi Zhang, graduate research assistant in SDSU's Department of Agricultural and Biosystems Engineering.

Certain areas have greater concentrations of microplastics than other areas, the researchers noted. The ambient air over urban areas contains a relatively high concentration of microplastic particles, primarily due to industrial production and other human activities. The outdoor environment of cities appears to be polluted by plastic particles from textiles, agricultural products and marine aerial microplastics.

But it’s not just outdoors where microplastics circulate. Recent data from a study conducted in Sri Lanka indicates that humans are more exposed to airborne microplastics in indoor environments compared to outdoor settings. In fact, estimated indoor exposure is significantly higher than outdoor exposure. This is compounded by the extended time that most individuals spend indoors.

How do they affect human health?

Over the past decade, there have been a number of studies examining the effect microplastics have on the human body. The studies reveal there is substantial evidence indicating that exposure to microplastics through respiration and ingestion could lead to various diseases affecting the respiratory, immune and nervous systems.

Understanding the potential effects of microplastics exposure on human health, from a toxicological perspective, is still in its infant stages. However, airborne microplastics exposure has been linked to oxidative stress, lipid metabolism disturbances, neurotoxicity and biomarker changes, all of which indicate potential ecotoxicity. Exposure to microplastics may be linked to many harmful health effects, including disruptions to the intestinal microbiota, liver toxicity, lung damage and reproductive system impairment.

The liver, a critical organ for the body's detoxification, synthesis and metabolism of foreign substances, is highly susceptible to the accumulation of microplastics found in the air. These particles enter the food chain, are ingested by à£à£Ö±²¥Ðãs and can ultimately accumulate in human livers, posing significant health risks.

The toxic mechanisms underlying microplastics' harmful effects on the liver are merely the tip of the iceberg. Studies have shown that some microplastics are absorbed by the body alongside other toxic substances, potentially leading to synergistic increases in toxicity. As a result, there is a pressing need for future longitudinal epidemiological research to investigate the relationship between airborne microplastics exposure concentrations and liver disease, Kumar said.

Due to their small size, surface reactivity and ability to carry hazardous contaminants, airborne microplastics can penetrate deep into the respiratory system, potentially inducing oxidative stress, inflammation and cytotoxicity in lung tissues. Chronic exposure has been linked to respiratory diseases, impaired lung function and potential systemic effects resulting from their translocation into the bloodstream. Despite these findings, the precise mechanisms by which inhaled microplastics cause lung damage have not been fully explained.

Exposure to airborne microplastics may have a more significant impact than ingestion and can affect the nervous system through various molecular pathways. A groundbreaking study on deceased individuals revealed that airborne microplastics can travel to the brain via the olfactory bulb, suggesting potential neurological risks.

Long-term exposure to airborne microplastics has been linked with an increased risk of cancer, studies have revealed.

The good news is the human respiratory system is capable of clearing a significant proportion of microplastics through processes such as mucociliary self-clearing. Both à£à£Ö±²¥Ðã and human bodies possess several mechanisms to facilitate the clearance of microplastics, including ciliary movement and phagocytosis by alveolar macrophages. Nevertheless, these mechanisms are not entirely effective in removing all microplastics.

What can be done now?

Kumar notes the need for more interdisciplinary research to better understand and regulate airborne microplastics in our environment. He also presented some steps that can be taken to minimize exposure to microplastics.

One step could be enhancing indoor ventilation in the home. Another is to decrease the use of synthetic fabrics. Kumar also suggests using a vacuum equipped with a high-efficiency particulate air filter when cleaning.

"Given the emerging nature of this field, further research is necessary to fully comprehend the sources, distribution and potential consequences of indoor microplastics on human health," Kumar said. "Additionally, it is essential to thoroughly document the impacts of inhaling and ingesting microplastics on human health to formulate effective prevention and treatment strategies for the future."

Contributing authors included Kumar; Zhang; Jordan Traub, graduate research assistant in SDSU's Department of Agricultural and Biosystems Engineering; ZhengRong Gu, professor in SDSU's Department of Agricultural and Biosystems Engineering; and Xufei Yang, assistant professor in SDSU's Department of Agricultural and Biosystems Engineering.