Toxic or hazardous air pollutants are suspected of causing cancer, asthma, reproductive effects, birth defects, nervous system damage, immune system damage, skin, eye, nose and throat irritation, brain, lung, kidney and liver damage, respiratory and cardiovascular diseases, and/or adverse environmental effects. Some examples of the 187 substances and 33 major urban air toxins currently being monitored and controlled are acetaldehyde, aldehydes, arsenic compounds, benzene, butadiene, cadmium compounds, chromium compounds, coke oven emissions, ethylene oxide, formaldehyde, mercury compounds, pesticides, polychlorinated biphenyls, polycyclic organic hydrocarbons, solvents, and vinyl chloride.

Most toxic air pollutants come from anthropogenic sources including: mobile sources (the largest contributor of emissions) such as cars, trucks, and buses; stationary sources (typically industry, which may be called point sources) such as factories, chemical plants, power plants, and refineries; building materials and cleaning solvents; and accidental releases including leaks and spills. Natural pollutants come from volcanic eruptions, forest fires, etc. Major sources of release of toxic or hazardous air pollutants include chemical plants, steel mills, oil refineries, hazardous waste incinerators, etc. Area-wide sources, which are much smaller, are an accumulation of pollutants from dry cleaners, gas stations, etc. Also off-road equipment such as construction equipment, farm equipment, small boats and ships contribute to the problem, as well as secondary chemical reactions between compounds in the atmosphere.

After the toxics are released into the air, they are carried by the wind to places near and far depending on weather conditions, the topography of the land, the physical and chemical properties of the pollutant, and the changes to the chemical that may occur while airborne. They may be deposited on land or in the water, then evaporate and recycle again. Some of the air toxics such as heavy metals may remain airborne for indeterminate periods of time.

Depending on the concentration and length of exposure to the air toxics and other factors concerning the individuals who are exposed to these pollutants, a variety of health effects may occur. Of the 187 substances listed by the US EPA, 33 are considered very hazardous in urban areas.

To determine potential health effects of a given air toxic or combination of toxics, it is necessary to do an evaluation of the exposure using a five-step process as follows:

  • 1. Identify the actual pollutants released.
  • 2. Determine the patterns of release of each of the chemicals and how much is released in a 24-hour period.
  • 3. Determine the amount of the pollutants that reach individuals and the concentration.
  • 4. Estimate the number of people who have been exposed to the pollutants and at what concentrations for what period of time. (See endnote 10.)
  • 5. Determine the number of slow-moving diesel trucks, their numbers of starts and stops and deliveries, in heavy industrial sections of the city where mostly poor people live. These underserved areas lead to greater exposure for the residents and it therefore becomes an environmental justice issue.

People are exposed to toxic air pollutants by:

  • • Inhaling quantities of contaminated air
  • • Eating quantities of contaminated food such as fish, meat, milk, eggs, fruits, and vegetables
  • • Drinking water contaminated by the deposition of toxic air pollutants
  • • Ingesting quantities of contaminated soil, primarily children
  • • Frequent skin contact with contaminated soil, dust, water, or air

Professional practitioners can then determine the potential health effects that individuals will have in reaction to the release of the contaminants. It is important to note that contaminants accumulate in the body and that mixtures of contaminants are much more frequent than single releases and this may well complicate the problems of diagnosis and prevention of short-term and long-term diseases.

To control toxic air pollutants, it is necessary to use pollution prevention measures such as product substitution, process modification, improved work practices, cleaning of coal, and cleaning of flue gas. Reduce emissions from cars, trucks, buses, and other vehicles. Use appropriate reformulated gasoline.

The major toxic air pollutants are (see endnotes 13, 18):

1. Diesel Fuel and Emissions

Diesel fuel and emissions create about 80% of the total estimated cancer risk of all hazardous air pollutants. Diesel exhaust, which comes from on-road as well as off-road mobile sources, as well as stationary sources, is a complex mixture of gases, vapors, and fine particles containing arsenic, benzene, nickel, carbon monoxide, nitrogen oxides, sulfur dioxide, hydrocarbons, etc. It is known to increase respiratory and cardiovascular diseases, which may lead to death. There is a significant increase in lung cancer associated with people who constantly inhale the fumes.

Best Practices for Diesel Fuel and Emissions

  • • Utilize cleaner fuels such as ultra-low sulfur diesel, biodiesel, and/or liquid petroleum gas.
  • • Retrofit the engine of older trucks and buses by installing emission-reduction equipment including catalysts.
  • • Repair existing engines to make them the same as the original engine.
  • • Use proper maintenance schedules to keep engines running properly.
  • • Reduce idling time throughout the usage of the vehicle.
  • • Increase the energy efficiency of the vehicle by using proper tires that are properly inflated.

2. Acrolein

Acrolein is emitted by industrial plants where it is manufactured as an intermediate for other chemicals. It is also found in tobacco smoke, forest fire smoke, gasoline and diesel exhaust, paper mills, and other non-metallic mineral and wood products. It is a registered pesticide in California and is also used to control fungi and bacteria. It causes irritation of the eyes, nose, throat, and respiratory tract and potentially pulmonary edema.

3. Benzene

Benzene is emitted mostly from gasoline motor vehicle exhaust, gasoline fugitive emissions, and to a much lesser extent, stationary industry sources. It is a widely used industrial chemical and is used in the manufacture of medicines, shoes, dies, detergents, explosives, etc. Benzene may also be found in tobacco smoke, heating and cooking systems, and evaporating from various products used within the home. It is a major contributor to overall cancer risk. It can cause central nervous system depression, nausea, tremors, drowsiness, intoxication, and unconsciousness.

  • 4. 1,3 Butadiene
  • 1,3 Butadiene is emitted from the incomplete combustion of gasoline and diesel fuels. It may also come from petroleum refineries, wearing of tires, residential wood burning, agricultural burning, and forest burning. It may be found in environmental tobacco smoke. It is used in the production of synthetic materials. It is irritating to the eyes and mucous membranes and may cause blurred vision, fatigue, headaches, and vertigo.
  • 5. Carbon Tetrachloride

Carbon tetrachloride in the past has been used for dry cleaning and as a green fumigant in the United States. Although it has been discontinued, it has an estimated lifetime in the atmosphere of 50 years and therefore can still be found upon testing. It affects the central nervous system and is a respiratory tract irritant as well as a toxin for various cell components.

6. Chromium

Electroplating and anodizing operations are used to coat metal parts and tools with a small amount of chromium to protect them from corrosion and wear. Hexavalent chromium, which is released during the electroplating and anodizing processes, is known to cause cancer. It may also cause complications with pregnancy and childbirth.

7. Coke Oven Emissions

Coke is used to extract metal from ores, especially iron, and is also used to make calcium carbide in the manufacture of graphite and electrodes. Coke oven batteries at steel plants convert coal into coke and in a blast furnace which converts iron ore to iron. The emissions contain benzene, which may cause cancer, conjunctivitis, severe dermatitis, and lesions of the respiratory and digestive systems.

8. Formaldehyde

Formaldehyde is used in the production of dies, textiles, particle board, plywood, as an embalming fluid, etc. It is hazardous to the respiratory system and skin, and is highly toxic. It may cause cancer.

9. Mercury

Mercury is a neurotoxin that bioaccumulates in the food chain. It is emitted to the atmosphere usually in its elemental form and remains viable for a long period of time, allowing it to be transported over great distances. During this time, it is oxidized and produces a reactive gaseous form which allows it to increase its rate of deposition in a variety of ecosystems.

10. Polycyclic Organic Matter

Polycyclic organic matter is produced by the combustion of fossil fuels and vegetable materials. The compounds may be found in ambient air from cigarette smoke, asphalt roads, coal tar, hazardous waste sites, motor vehicles exhaust, smoke from wood burning in homes, fly ash from electric power plants using coal, petroleum refineries, and paper mills. They may cause health problems in the gastrointestinal tract, liver, skin, eyes, etc.

They may affect reproduction and also increase the risk of lung cancer. PAHs are part of this group and the most frequently monitored of these is benzo [a] pyrene, which has been found in urban air at twice the level found in rural air. (See endnote 26.)

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