Air Pollutants: How Do They Enter Our Bodies?

Indoor air pollution is a serious threat to human health, causing millions of deaths each year. Indoor air pollutants can enter the body in various ways, with inhalation being the most commonly assumed route. However, recent studies have shown that the skin, as the body's largest organ, can be a significant pathway for the entry of certain toxic air pollutants. These pollutants include phthalates, parabens found in cosmetics and sunscreens, nicotine, synthetic musks, pesticides, and solvents. Additionally, indoor air pollutants can be released from building materials, furnishings, cleaning products, and human activities such as smoking, cooking, and burning solid fuels. Inadequate ventilation and outdoor air quality can also impact the concentration of indoor air pollutants, affecting the health and comfort of building occupants. Understanding the sources and pathways of indoor air pollutants is crucial for developing strategies to protect human health and enhance indoor air quality.

Inhalation

The respiratory system is frequently the primary target of indoor air pollutants because pollutants often enter the human body through inhalation. Indoor air is often between two and five times more polluted than outdoor air, and in some cases, it can be up to 100 times worse.

Indoor air pollutants can come from various sources, including outdoor air pollutants that find their way indoors and become trapped due to inadequate ventilation. Inadequate ventilation can increase indoor pollutant levels by not bringing in enough outdoor air to dilute emissions from indoor sources and by not effectively removing indoor air pollutants. High temperatures and humidity levels can also increase concentrations of some pollutants.

Common indoor pollutants include smoke, vapours, mould, and chemicals found in paints, furnishings, and cleaning products. Some specific examples of indoor air pollutants and their sources include:

• Radon: A colourless, odourless, naturally occurring gas that comes from the decay of radioactive elements in soils. It can enter indoor spaces through cracks or gaps in buildings. Radon exposure is the second leading cause of lung cancer among non-smokers in the United States.
• Carbon monoxide (CO): Produced mainly by combustion processes such as cooking or heating, and can also infiltrate indoor environments from outdoor sources. Sources of indoor CO emissions include unvented kerosene and gas space heaters, leaking chimneys and furnaces, back-drafting from various sources, gas stoves, generators, and tobacco smoke.
• Nitrogen oxides: The two principal nitrogen oxides are nitric oxide (NO) and nitrogen dioxide (NO2), which are associated with combustion sources such as cooking stoves and heaters. When gas stoves and heaters are used, indoor levels of these pollutants often exceed outdoor levels.
• Volatile organic compounds (VOCs): Common indoor sources of VOCs include tobacco smoke, stored fuels, vehicle exhaust from attached garages, and formaldehyde, which is found in plants, fruits, vegetables, animals, and humans. Benzene, a known carcinogen, is another VOC that can be found indoors.
• Particulate matter (PM): PM is defined as carbonaceous particles associated with adsorbed organic chemicals and reactive metals. Its main components include sulfates, nitrates, endotoxin, polycyclic aromatic hydrocarbons, and heavy metals. Depending on particle size, PM can be classified as coarse, fine, or ultrafine particles, with the latter being easily inhaled and deposited into the lungs, where they can enter the bloodstream and travel to vital organs.

The health effects of indoor air pollutants can vary, and some people may be more sensitive to certain pollutants than others. Immediate effects may include irritation of the eyes, nose, and throat, headaches, dizziness, and fatigue. Prolonged exposure to certain indoor air pollutants has been linked to more severe health issues, including respiratory infections, asthma, lung cancer, and other types of cancer.

Poor ventilation

Indoor air pollutants can originate from various sources, including fuel-burning appliances, construction materials, and outdoor air pollution. Inadequate ventilation fails to dilute and remove these pollutants, leading to their concentration in the indoor environment. High temperatures and humidity levels further exacerbate this issue, as they can increase the concentration of certain pollutants.

The respiratory system is often the primary target of indoor air pollutants, as they are inhaled and can penetrate deep into the lungs. Pollutants can also enter the bloodstream, causing or worsening respiratory and cardiovascular issues. For example, exposure to indoor air pollution has been linked to increased risks of respiratory infections, lung cancer, and heart disease.

Some signs of poor ventilation include moisture condensation on windows or walls, persistent odours, and mould growth. These issues not only indicate inadequate ventilation but can also contribute to the deterioration of indoor air quality.

To address poor ventilation, it is essential to improve the ventilation system's design and operation. Mechanical ventilation devices, such as fans or blowers, can be utilized to increase the exchange of indoor and outdoor air, diluting pollutants and creating a healthier environment. Additionally, natural ventilation through opened windows and doors can also help improve air circulation and reduce the concentration of indoor pollutants.

Building materials

Older building materials can release indoor air pollutants when disturbed or removed. For example, tearing out or demolishing older tiles, insulation, or drywall can release dangerous chemicals into the air or create harmful dust. Plasticizers in some flooring, pipes, and other materials have been linked to a range of potential health problems.

In addition to the materials themselves, the construction and installation processes can also contribute to indoor air pollution. For instance, "Chinese drywall," installed in buildings along the Gulf Coast states and Virginia between 2001 and 2009, was found to give off high levels of hydrogen sulfide. Similarly, laminate flooring manufactured in China between 2012 and 2014 emitted high levels of formaldehyde.

To protect indoor environments from these pollutants, it is essential to choose building materials wisely. Look for materials and paints with low or no emissions, and ensure proper ventilation during and after installation.

Human activities

One of the primary ways human activities contribute to indoor air pollution is through the use of various products and the discharge of waste gases. This includes tobacco smoking, burning solid fuels, cooking, and cleaning. Tobacco smoke releases toxic chemicals like formaldehyde and lead, which are harmful to human health. Cooking, especially with fuel-burning stoves, contributes to the presence of carbon dioxide (CO2), sulfur dioxide (SO2), carbon monoxide (CO), nitrogen dioxide (NO2), and particulate matter (PM). Inadequate ventilation in indoor spaces can further increase pollutant levels by not effectively removing emissions from these activities.

The use of certain products and materials in construction, building maintenance, and furnishing can also introduce pollutants. For example, paints, carpets, new furniture, and cleaning agents can emit volatile organic compounds (VOCs) and other chemicals. Some construction materials, such as asbestos, can release tiny fibres into the air if disturbed.

Additionally, human activities can create favourable conditions for the growth of biological contaminants. These include mould, viruses, bacteria, pollen, spores, dust mites, cockroaches, and other insects. Poor ventilation, high humidity, and moisture indoors contribute to the growth of these contaminants, which can trigger allergic reactions and respiratory issues.

The pollutants generated by these human activities can enter the human body primarily through inhalation. The respiratory system is frequently the primary target of indoor air pollutants, as the pollutants are breathed in and can affect the lungs and heart, causing serious health issues.

Outdoor pollutants

Outdoor air pollution is a significant environmental health issue, affecting individuals in low-, middle-, and high-income countries. It is caused by the presence of harmful substances in the air, such as dust, fumes, gases, mist, odours, smoke, and vapours, which can have detrimental effects on human health. The main route of exposure to outdoor air pollution is through the respiratory tract, with inhalation leading to inflammation, oxidative stress, immunosuppression, and mutagenicity in cells throughout the body.

Outdoor air pollution is composed of various pollutants, including particulate matter (PM), carbon monoxide (CO), ozone (O3), nitrogen dioxide (NO2), and sulphur dioxide (SO2). These pollutants are released into the atmosphere through anthropogenic activities, such as the combustion of fuels in the transportation and industrial sectors. The health impacts of outdoor air pollution are far-reaching, affecting almost every organ in the body. It is a risk factor for all-cause mortality and is particularly linked to cardiovascular and respiratory diseases, cancers, and adverse pregnancy outcomes.

Children are especially vulnerable to the effects of outdoor air pollution due to their small and developing airways, higher breathing rate relative to their size, and less developed immune systems. Growing up in highly polluted areas can negatively impact lung development, increasing the risk of lung disease later in life. Older adults are also at increased risk due to age-related reductions in lung function and a less effective immune system to combat the effects of inhaled contaminants.

Individuals who work outdoors are at a higher risk of exposure to outdoor air pollution due to the amount of time they spend outdoors and the strenuous nature of their work, which increases their breathing rate and the amount of polluted air inhaled. Certain areas, such as those experiencing rapid population growth or with newly constructed industrial sources, may have higher concentrations of pollutants, exacerbating the exposure risk for residents and outdoor workers.

While the concentration of outdoor air pollutants may decrease when transported indoors, human exposure to these pollutants is continuous across microenvironments, including indoor spaces. The complex interplay between the composition and magnitude of outdoor air pollution, human activity patterns, and individual susceptibility determines the overall health impact of exposure.

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