TABLE 2.

Examples of Environmental Contaminants Associated with Respiratory Health^a

Environmental Contaminant	Sources	Key Recognized or Possible Respiratory Health Effect
Particulate matter (PM)	• PM is a mixture of solid and/or liquid suspended air particles • Human sources include traffic, road dust, industrial sources (combustion of fossil fuels, metallurgy, ceramics, and others), domestic fuel combustion, and other human activities74 • Natural sources include wildfires, soil dust, and sea salt	• Associated with all-cause and respiratory-related mortality75; lowered life expectancy76 • Asthma symptoms and exacerbation77 • Coughing, wheezing, and breathlessness41,78 • Impaired lung development in children23,25 • Impaired lung function in adults79
Ozone (O3)	• Formed as a product of chemical reactions between sunlight, nitrogen oxides (NOx), and volatile organic compounds (VOCs) • May be emitted from various sources, including traffic, power plants, refineries, chemical plants, and other sources80	• Decreased lung function and lung function growth81 • Asthma symptoms and exacerbation82 • Allergic responses with coexposure to allergens37
Nitrogen dioxide (NO2)	• Formed in high-temperature combustion processes such as power plants, traffic, and off-road vehicles83	• Decreased lung function21,84–86 • Asthma exacerbations82
Sulfur dioxide (SO2)	• May arise from combustion of sulfur-containing fuels (such as coal) in power plants and other industrial processes, metal extraction, and heavy vehicles87 • May also arise from natural sources such as volcanic eruptions	• Eye and upper airway irritation • Alterations to lung function88 • Asthma exacerbations82
Traffic-related air pollution (TRAP)	• Combustion of diesel and gasoline in motor vehicles • Roadways, especially those with high traffic density can be significant sources of TRAP	• Decreased lung function21,25,84 • Asthma symptoms and exacerbations • Respiratory infections89
Environmental tobacco smoke	• Smoking (cigarettes and other tobacco related products) • Second-hand smoke • Vaping/electronic cigarettes	• Lower respiratory illnesses in infants and children, including asthma, respiratory infections90 • Decreased lung growth in children91 • Impaired lung function91 • Asthma, asthma exacerbations, severity92,93
Plasticizers (eg, phthalates)b	• Present in many consumer products (eg, building materials such as polyvinyl chloride flooring, food packaging, personal care products such as hair and skin care products, toys, medications, medical tubing) • Ingestion of contaminated foods/beverages is thought to be the primary route of exposure, but inhalation and dermal absorption also plausible • Found in air, dust, food	• Asthma/allergic symptoms and exacerbations, asthma severity46,94 • Rhinoconjunctivitis, atopic dermatitis95,96 • Airway inflammation95
Formaldehyde	• Smoke from cigarettes and other tobacco products, gas stoves, and open fireplaces • Select manufactured wood products such as cabinets, furniture, plywood, particleboard, and laminate flooring • Permanent press fabrics such as those used for curtains/drapes or on furniture • Household products such as glues, paints, caulks, pesticides, cosmetics/personal care products, and detergents	• Irritation of the nose, eyes, and throat97 • Headache, runny nose, nausea, and difficulty breathing/wheezing • Asthma exacerbations and other respiratory symptoms98,99
Radon (Rn)b	• Product of the natural radioactive decay of uranium that has further decayed to radium found in soil and rocks100,101	• Lung cancer risk102 • Possible association with chronic obstructive pulmonary disease (COPD)103 and COPD mortality104 • Emerging evidence of possible risk of airway inflammation in childhood asthma

^aThis list is not meant to be exhaustive and includes contaminants for which there is sufficient or suggestive/emerging evidence of adverse effects on lung health from human and animal studies.

^bAlthough findings from human studies are not conclusive at this time, some studies suggest that select exposures could impact pediatric respiratory health.