Air Pollution: Particulate Matter

• Ambient particulate air pollution is the sixth-leading risk factor and the top environmental risk factor for worldwide deaths as of 2019.
• Air pollution is anything in the atmosphere dangerous to people, animals, or the environment.
• The two main components that pollute the air are gasses and particulates
• Gases include ozone and sulfur dioxide.
• Particulates are microscopic bits of solid or liquid particles that are light enough to be suspended in the atmosphere.
• Particulate matter (PM) is grouped by the size of individual particles.
• Size determines how easily particles interact with our bodies when entering our lungs.
• PM is measured in micrometers.
• The two major size classes of PM are PM10, particles under 10 micrometers in diameter, and PM2.5, particles smaller than 2.5 micrometers in diameter.

Environmental Pollutants

• Insoluble particles and fibers: Airborne Particulate Matter (APM), Asbestos, and Nanoparticles.
• Gases: Nitrogen Dioxide (NO₂), Sulfur Dioxide (SO₂),and Ozone.
• Mixtures: Tobacco Smoke, Fossil Fuel/Diesel Exhaust, and Smog.
• APM originates from man-made sources, natural sources, and fires.

APM Size

• The size of APM matters regarding its effects.
• PM2.5 includes combustion particles, organic compounds, and metals, having a diameter of less than 2.5 µm.
• PM10 includes dust, pollen, and mold, having a diameter of less than 10 µm.
• PM10, are inhalable coarse particles, with a diameter of 2.5-10 μm.
• PM2.5, are fine particles with a diameter of 2.5 μm or less.
• The WHO designates airborne PM as a Group 1 carcinogen.
• APM penetrates deep into the lungs and blood streams unfiltered, causing permanent DNA mutations, heart attacks, respiratory disease, and premature death.

Safe Levels of Particulates

• There is no safe level of particulates.
• For every ↑ of 10 µg/m³ in PM10, the lung cancer rate rises 22%.
• For every ↑ of 10 µg/m³ in PM2.5, the lung cancer rate rises 36%.

PM2.5 Short-term Effects

• Cough and breathing difficulty
• Eye, nose, and throat irritation
• Headache
• Anxiety
• Skin irritation
• Allergies and acute lower respiratory infections

PM2.5 Long-term Effects

• Stroke
• Cardiovascular diseases
• COPD
• Lung cancer and chronic respiratory infections
• Diabetes
• Different size particulate matter affects different areas in the respiratory system.
• PM2.5 enters the human body through the respiratory tract and then enters the blood stream through diffusion.

Air Quality Index (AQI)

• The AQI is the US Environmental Protection Agency (EPA)'s index for reporting air quality.
• AQI is a tool for communicating air quality and its impact on health.
• A higher AQI signifies greater air pollution and a greater health concern.
• An AQI of 50 or below is considered good air quality.
• An AQI over 300 is considered hazardous air quality.

Air Quality Index for Particle Pollution

• 0-50 is good, with no health advisory
• 51-100 is moderate, advising unusually sensitive people to consider reducing prolonged or heavy exertion.
• 101-150 is unhealthy for sensitive groups, recommending those with heart or lung disease, older adults, and children to reduce prolonged or heavy exertion.
• 151-200 is unhealthy, advising people with heart or lung disease, older adults, and children to avoid prolonged or heavy exertion, and everyone else should reduce prolonged or heavy exertion.
• 201-300 is very unhealthy, advising individuals with heart or lung disease, older adults, and children should avoid all physical activity outdoors and everyone else should avoid prolonged or heavy exertion.
• The lungs are the major site of environmental toxicology.
• The lung encounters every kind of insult that causes disease (e.g., bacteria, viruses, fungi, gasses, airborne fibers and particulates, heavy metal vapors).
• The lung is the primary interface of the immune system with the environment.
• Branching airways terminate in alveoli, the gas exchange unit in the lung.
• Main bronchi branch into bronchi and bronchioles, and terminate in >300 million alveoli, resulting in a surface area of more than 100 square yards.
• Compounds inhaled into the lung can be distributed throughout the body in minutes because of its interface with the vasculature.
• Hair-like projections called cilia line the primary bronchus to remove microbes and debris from the interior of the lungs.
• Ciliated epithelial cells and mucus-secreting goblet cells that line the airways comprise the primary defense mechanism, by which inhaled organisms and particles are expelled from the lung.
• Macrophages and lymphocytes patrol the lung and facilitate immune responses.
• Toxicants can spread from the lung to other regions of the body.

Respiratory Diseases Associated with APM

• Asthma: A chronic disease that causes inflammation in the bronchial tubes.
• Chronic Bronchitis: Inflammation of the bronchial tubes; bronchitis caused by PM inhalation is most likely chronic.
• Chronic Obstructive Pulmonary Disorder (COPD): A group of chronic lung diseases that makes it hard to breathe. Airflow through the airways leading to and within the lungs is partially blocked, resulting in difficulty breathing.
• Lung Cancer: Cells start to grow rapidly in an uncontrolled manner.
• Pneumonia: A serious infection that affects the lungs and can result from bacterial or viral infections, or any other irritant that could infect or irritate the sensitive lining of lungs.
• Airways produce more mucus than they would normally when exposed to irritants over time, leading to inflammation in the bronchial tubes.
• Inflammation and extra mucus reduce airflow and cause coughing.
• Mucus production and inflammation over years lead to progressive and permanent lung damage.
• Chronic lung diseases (asthma, COPD, fibrosis, etc.) are characterized by continuous cycles of cell injury and repair that culminate in loss of tissue architecture and function.
• Many of these changes are irreversible, and after years of damage, fatal.
• Exposure to APM leads to oxidative stress and inflammation that alter susceptibility to lung disorders (asthma and COPD).
• The lung epithelium and the vascular endothelium is affected by phagocytosis by macrophages results in the release of reactive oxygen species.
• Antioxidant responses prevent injury but no therapy using antioxidants has been directly effective at reducing this response.

Asbestos

• Asbestos include six types of naturally occurring mineral fibers.
• Chrysotile makes up ~95% of asbestos in the U.S.
• Vermont was one of two states that produced the material (beside CA).
• Mining started in Vermont in 1889, and by 1930, nearly all asbestos in the nation came from here.
• The mine closed in 1993.

Toxicity of Asbestos Fibers

• Chrysotile is positively charged and causes cellular lysis at high concentrations.
• Crocidolite and Amosite are neutral/negatively charged, more toxic, and generate oxidants by iron-dependent reactions and phagocytosis.
• Asbestos is classified as a Class I Carcinogen.
• Asbestos fibers can penetrate lungs causing lung injury.
• Longer asbestos fibers are more carcinogenic and more toxic than short fibers.
• Asbestos exposure is linked to respiratory diseases and include lung cancer, asbestosis (fibrosis), and Mesothelioma.

Mechanism of Action of Asbestos

• Inflammation
• ROS generation
• DNA damage