Clean air generally consists of 78% nitrogen gas and 21% oxygen and 1% of a mixture of gases (primarily argon, carbon dioxide, methane, hydrogen and helium). The less than desirable substances that lead to polluted air are classified by the EPA as “criteria” air pollutants. The NAAQS was established by the EPA for the six “criteria” air pollutants in the air, and are currently set for carbon monoxide, lead, ground-level ozone, nitrogen dioxide, particulate matter and sulfur dioxide. The EPA classifies these substances as “criteria” air pollutants because it sets regulations and guidelines for clean air by using permissible levels of these substances. These six main pollutants have various causes unique to each substance. The most significant sources of Carbon Monoxide (CO) are vehicles and machinery that burn fossil fuels, in addition to this, many items in our homes can release CO into the atmosphere, such as gas stoves and gas space heaters. Lead (Pb) present in our air is attributed to multiple sources, these include lead-acid battery manufacturers, waste incinerators, lead smelters and more. Ground Level Ozone (O3), also known as “bad” ozone, occurs as consequence of chemical reactions between nitrogen oxides and volatile organic compounds in the presence of sunlight. The reactants of these reactions are present as product of motor vehicle exhaust, gasoline vapors and emissions from industrial facilities. Nitrogen Dioxide (NO2) emissions occur due to the burning of fuel emitted by vehicles, power plants and heavy equipment. Particulate Matter is a mixture of solid particles and liquid droplets present in the air. These mixtures can be a result of hundreds of different chemicals, primarily pollutants emitted from power plants and automobiles. Sulfur Dioxide(SO2) is present in the atmosphere because of the burning of fossil fuels, as well as the extraction of metal from ore, volcanoes, and anything burning sulfur or materials containing sulfur. These pollutants are the main contributors in air pollution. Aside from the nervous system, there are additional detrimental effects on the human body. Investigations of air quality changes show that in events of pollution, hospital admission and mortality rates increase. The variables of composition of air pollutants, dosage and time intervals of exposure and exposures of pollutant mixtures rather than specific individual substances equate to multiple diverse impacts on health. These effects can range from birth defects to lung cancer, many health problems are linked to air pollution, they include asthma, emphysema, reduced immune system, cancer, skin irritation, nephrocalcinosis, liver damage and several other conditions.
The toxins that cause problems to our nervous system exist in the atmosphere and all around us, but how they enter into our nervous system is a notable process. Long term exposure to high levels of toxins found in polluted air sometimes results in interaction with the central nervous system where the toxins are distributed throughout our bodies many cavities and paths. (Figure 1). Alternatively, from entering directly into the central nervous system, toxins can be released from other organs and absorption sites. The release of these toxins can lead to neuroinflammation and neurodegeneration in the central nervous system. When this occurs, it is then followed by the production of proinflammatory cytokines, which cause the blood vessels of our brains to produce constitutive expression of receptors. Airborne toxins may create neuroinflammatory responses more immediate in the sense that it activates our immune systems. The very small ultrafine particles can easily bypass cell membranes and barriers in the lung and the brain, this is because of their small microscopic size. In addition, a more direct route for ultrafine particles is the olfactory mucosa, a neuronal epithelium, which unfortunately happens to be in direct contact with air outside of our bodies, the polluted air. (Genc 2012)
The effects of air pollution on the nervous system is primarily due to heavy metals present, but since concentration of individual toxic substances is variable and mixtures are more accurate descriptions of the pollutants entering the body, the substances are addressed as toxins in general.
The following tables exhibit the experimental studies used in the journal of toxicology’s investigation into the effects of air pollutants on the human nervous system
Strokes are an example of some of the central nervous system disorders caused by toxins found in environmental air. The relationship between air pollutants and strokes was first recorded after the Great London Fog, similar results have since been obtained across the world.
In the early 2000s, crazed dogs found in Mexico City offered preliminary hints that the intake of polluted air could perhaps be the cause for neurodegeneration. Neuroscientist Lilian Calderón-Garcidueñas, of the University of Montana in Missoula, noticed that the aging dogs who lived in particularly polluted areas of the city often became addled, growing disoriented and even losing the ability to recognize their owners. When the heavy metals and toxins reach the brain it was shown to cause major inflammation and plaque, causing neurodegenerative diseases. The link between Alzheimer’s and air pollutants has become more evident through studies in Translational Psychiatry that concluded air pollution is responsible for 21% of cases.
Besides the ‘criteria’ air pollutants, mercury is a dangerous heavy metal found in polluted air. Mercury has an incredibly negative effect on pregnant mothers