The Clean Air Act requires EPA to address 188 toxic air pollutants. Some air toxics are released from natural sources such as volcanic eruptions and forest fires. People exposed to toxic air pollutants at sufficient concentrations and for sufficient durations have an increased chance of getting cancer or experiencing other serious health effects. Some toxic air pollutants pose particular hazards to people at a certain stage in life, such as young children or the elderly.
Some health problems occur very soon after a harmful exposure.
Health effects associated with long-term exposures to toxic air pollutants, however, may develop slowly over time or not appear until many months or years after the initial exposure. Toxic pollutants in the air or deposited on soils or surface waters can have a number of environmental impacts. Like humans, animals experience health problems if exposed to sufficient concentrations of air toxics over time. Persistent toxic air pollutants that can accumulate in plants and animals are of particular concern in aquatic ecosystems because the pollutants accumulate in tissues of animals, magnifying up the food chain to levels many times higher than in the water. Toxic pollutants that disrupt the endocrine system also pose a threat.