By Sarah Kirsh
Air pollution today includes a wide variety of chemicals that are present throughout American air and cities. As of today’s climate, The United States Environmental Protection Agency establishes standards for the six most common pollutants otherwise known as “criteria” pollutants: carbon monoxide, lead, nitrogen dioxide, ozone, particulate matter, and sulfur dioxide. The two “criteria” pollutants that have been researched to impact mental health are particulate matter and ozone. First, The United States Environmental Protection Agency defines particulate matter as “a mixture of solid particles and liquid droplets found in the air” This pollutant is classified into two subdivisions: particulates with a diameter of 2.5 micrometers (PM) and particulates with a diameter of 10 micrometers (PM). Due to the long term presence of these pollutants in the air, damages to mental and physical health are more than a possibility, but a certainty.
As these pollutants swarm the air and human respiratory systems, there are several chemical pathways in which air pollutants can affect mental health. One widely known and supported pathway is oxidative stress. According to Healthline, oxidative stress is “an imbalance between free radicals and antioxidants in your body.” Free radicals have an uneven number of electrons, resulting in a very unstable molecule. Due to their unstable nature, free radicals are likely to bond to any molecule, causing harmful reactions in the body, including changing the structure and function of proteins, lipids, and DNA. According to Virginia Commonwealth University Medical Campus researcher Michelle L. Block and University of Montana researcher Lilian Calderon-Garciduenas, ozone exposure has been proven to cause oxidative stress. In a broad sense, oxidative stress “modifies aggregation and rate of protein fibrillation, potentially affecting soluble Aβ and α-synuclein”, critical proteins in the brain. Accumulation of the abnormally structured forms of these specific proteins is known to contribute to both Alzheimer’s disease and Parkinson’s disease. More specifically, ozone-induced oxidative stress may lead to “neuronal morphological damage, motor deficits, and memory deficits.”
The second most supported way in which pollutants may influence brain chemistry is neuroinflammation. Simply put, neuroinflammation is the inflammation of nervous system tissue. Neuroinflammation, in the case of air pollutants, starts with the immune cells of the central nervous system: microglia. Similar to the immune system, microglia eat up any potentially harmful chemicals or pathogens in the brain. Once microglia detects any pathogen, the cells become activated. While usually helpful, Block & Calderon-Garciduenas state that “activated microglia can become a chronic source of pro-inflammatory factors,” causing neuroinflammation. Both ozone and particulate matter are linked to this swelling of brain tissue. Air pollutants activate microglia in several ways, most commonly by being mistaken as pathogens or damaging neurons. Moreover, in recent brain scans and studies, there has been increased activated microglia and chronic inflammation in patients with Alzheimer's disease and Parkinson’s disease. Like oxidative stress, neuroinflammation may wreak havoc in countless ways, simply because the chemistry of the brain is off balance.
Not only are neurodegenerative diseases subject to increase from air pollution exposure, but mental health diseases and conditions are as well. The first concern comes from particulate matter. In a study conducted at Northeastern University’s Department of Health Sciences, researchers Vivian C. Pun, Justin Manjourides, and Helen Suh concluded that there is an association between PM exposure and depression and anxiety symptoms. Even after adjusting for confounding factors, including socioeconomic measures, the results were statistically significant. In another study done at the University College London’s Institute for Health Informatics and Division of Psychiatry, researchers Isobel Braithwaite, Shuo Zhang, James B. Kirkbride, David P. J. Osborn, and Joseph F. Hayes, further researched this association. Their analysis concluded a statistically significant positive association between long-term PM exposure (more than 6 months) and anxiety and depression. However, the study found another mental health risk, one that Pun et al. had not evaluated. According to Braithwaite et al., there is a statistically significant positive association between short term PMexposure (less than 6 months) and suicide. Yet, these are only the possible effects of particulate matter alone. Ozone has its own range of risks. Researchers from several divisions of Italy’s Department of Health, F. Bernardini et al., conducted a study into the tangible effects of ozone. From almost 2,000 emergency department admissions for mental disorders, Bernardini et al. found a statistically significant association between short-term ozone exposure and a daily number of admissions to psychiatric emergency services. Thus, depression, anxiety, suicide, and any number of other mental illnesses can develop or increase from exposure to particulate matter and ozone.
Air pollution, mainly particulate matter and ozone, may deteriorate mental health and generate a wide range of diseases. Such unfortunate developments can be attributed to pollutants’ ability to trigger oxidative stress and neuroinflammation. Resultantly, the validity of these effects and possibly other health effects must be researched. Once further information gives scientists a more complete analysis, modern medicine may slowly develop to prevent these mental health concerns.
References:
Bernardini, F., Attademo, A., Trezzi, R., Gobbicchi, C., Balducci, P. M., Del Bello, V., . . . Tortorella, A. (2019). Air pollutants and daily number of admissions to psychiatric emergency services: Evidence for detrimental mental health effects of ozone. Epidemiology and Psychiatric Sciences, 29(66), 1-7. https://doi.org/10.1017/S2045796019000623
Block, M. L., & Calderon-Garciduenas, L. (2009). Air pollution: Mechanisms of neuroinflammation & CNS disease. Trends in Neuroscience, 32, 506-516. https://doi.org/10.1016/j.tins.2009.05.009
Braithwaite, I., Zhang, S., Kirkbride, J. B., Osborn, D. P. J., & Hayes, J. F. (2019). Air pollution (Particulate matter) exposure and associations with depression, anxiety, bipolar, psychosis and suicide risk: A systematic review and meta-analysis. Environmental Health Perspectives, 127(12), 1-23. https://doi.org/10.1289/EHP4595
Healthline. (n.d.). Everything you should know about oxidative stress. Retrieved from https://www.healthline.com/health/oxidative-stress
Pun, V. C., Manjourides, J., & Suh, H. (2017). Association of ambient air pollution with depressive and anxiety symptoms in older adults: Results from the NSHAP study. Environmental Health Perspectives, 125(3), 342-348. https://doi.org/10.1289/EHP494
United States Environmental Protection Agency. (n.d.a). Ground-level ozone pollution. Retrieved from https://www.epa.gov/ground-level-ozone-pollution/ground-level-ozone-basics#formation
United States Environmental Protection Agency. (n.d.b). National air quality: Status and trends of key air pollutants. Retrieved from https://www.epa.gov/air-trends
United States Environmental Protection Agency. (n.d.c). Particulate matter (PM) pollution. Retrieved from https://www.epa.gov/pm-pollution/particulate-matter-pm-basics#PM
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