Automotive Exhaust Chemicals: Disease Causing Effects

A short list of the likely pathogens in car exhaust:

  • Carbon Monoxide
  • Nitrogen dioxide
  • Sulphur dioxide
  • Suspended particles, PM-10 particles less than 10 microns in size
  • Benzene
  • Formaldehyde
  • Polycyclic hydrocarbons

Background Information - Adverse Health Effects of Chronic Exposure to Petroleum Combustion Products. On November 18, 1994, the first-ever conference on "Air Pollution: Impacts on Body Organs and Systems" was held in Washington, D.C. by the National Association of Physicians for the Environment. An abridged version follows. The relevance of this perspective increases with increasing air pollution and climate change. 2009 Update.

Jaffe and Badman at the same conference summarized the effects of polluted air :

"Blood perfuses all of the body's organs and can carry toxic substances as well as beneficial substances, such as oxygen, to them. Air pollution is the source of many materials that may enter the human bloodstream through the nose, mouth, skin, and the digestive tract. Chemicals known to be harmful, such as benzene, lead and other heavy metals, carbon monoxide, volatile nitrites, pesticides, and herbicides. These substances have been shown to produce harmful effects on the blood, bone marrow, spleen, and lymph nodes. Blood cells are constantly undergoing turnover, with new blood cells entering the circulation as mature cells are lost, making the blood system especially vulnerable to environmental poisoning. For example, lead interferes with normal red blood cell formation by inhibiting important enzymes. In addition, lead damages red blood cell membranes and interferes with cell metabolism in a way that shortens the survival of each individual cell. Each of these harmful effects can result in anemia.

Common air pollutants also have an affect on blood and thus on organs of the body. For example, carbon monoxide binds to hemoglobin two hundred times more avidly than oxygen and distorts the release to the tissues of any remaining oxygen. Thus, CO poisoning is a form of suffocation. Carbon monoxide can exacerbate cardiovascular disease in humans. Some airborne chemicals stimulate the immune system to activate leukocytes and macrophages that can produce tissue damage, especially to the cells that line human blood vessels. The combined effect of these events is to accelerate the changes that eventually lead to hypertension and ischemic heart disease.

Cory-Slechta and Lundberg discussed the adverse effects of pollution on the central nervous system: "The central nervous system (CNS) is the primary target for many serious air pollutants, such as lead, which is a major environmental hazard. Research provided evidence that levels of lead exposure associated with central nervous system effects, particularly as manifest in behavioral changes was lower than previously realized. Blood lead concentrations in children were not considered problematic until they exceeded 30 to 40 micrograms per deciliter ('g/dL); however, studies demonstrated changes in cognitive function at blood concentrations as low as 10 to 15 'g/dL. While children are more susceptible to lead's CNS effects, adults exhibit similar deficits in learning and memory. Advanced aging increases vulnerability to the toxic effects of lead. In Germany, a large study documented an age-related decline in bone lead concentrations with advancing age. This effect was more pronounced in women than in men, reflecting post-menopausal processes in women which contribute to bone resorption and the release of lead back into the bloodstream. These results mean that brain lead exposure is actually increased during a period of already heightened susceptibility due to concurrent degeneration of other physiological functions, including both CNS and renal functions.

Although lead is the most studied of hundreds of known or suspected neurotoxic air pollutants, other heavy metals, pesticides, and organic solvents also cause neurobehavioral dysfunction. Expanded research in behavioral neurotoxicology is urgently needed. Changes in mood, cognition, and behavior are endpoints that need to be evaluated in addition to cancer rates or mortality data and may be more common. In various studies, increased levels of air pollutants are accompanied by increased psychiatric emergency calls and hospital admissions, behavior changes, and a lessened sense of well-being. Irritating odors and cigarette smoke have been found to increase aggressive behavior, and to decrease helping behavior and altruism, leading to a degradation of social interaction."

Goldstein and Albright discussed immune system effects: "The effects of airborne pollutants on the immune system have been most widely studied in the respiratory tract. An airborne pollutant may enter the respiratory tract as a volatile gas (e.g., ozone, benzene), as liquid droplets (e.g., sulfuric acid, nitrogen dioxide), or as particulate matter (e.g., components of diesel exhaust, aromatic hydrocarbons). These pollutants interact with the immune system and may cause local and systemic responses ranging from overactive immune responses to immunosuppression. Most airborne pollutants are small molecular weight chemicals that must be coupled with other substances (e.g., proteins or conjugates) before they can be recognized by the immune system and cause an effect. Some disorders which may occur because of pollutants in the respiratory system are the following:

Immunosuppression can be demonstrated following exposure to polycyclic aromatic hydrocarbons (e.g.,tetrachlordibenzo-p-dioxin). Hypersensitivity reactions (e.g., occupational asthma) can occur following exposure to toluene diisocyanate and other volatile chemicals. There is clearly an underlying genetic basis for susceptibility to immunologic disease resulting from exposure to pollutants, but knowledge in this area is rudimentary at this time. For example, there is little understanding of genetically-determined susceptibility or resistance to pollutant-induced immune disorders. There is a lack of appropriate in vitro models, and it is difficult to identify specific, biologically-active substances that may be linked to immune disorders."

A Closer Look at Hydrocarbons

Benzene: The greatest possibility for high-level exposures is in the workplace... most people are exposed to benzene in tobacco smoke and automobile exhaust. Benzene has been found in at least 337 of 1177 US National Priorities List hazardous waste sites. Benzene and other less known hydrocarbons are produced in petroleum refining, and are widely used as solvents and as materials in the production of industrial products and pesticides. Benzene also is found in gasoline and in cigarette smoke. Other environmental sources of benzene include gasoline (filling) stations, underground storage tanks that leak, wastewater from industries that use benzene, chemical spills, groundwater next to landfills containing benzene, and food products that contain benzene naturally. Brief Exposure at High Levels--Death may occur in humans and animals after brief oral or inhalation exposures to high levels of benzene. Low concentrations of benzene causes drowsiness, dizziness, and headaches. Benzene has a suppressive effect on bone marrow and it impairs blood cell maturation and amplification. Benzene exposure may result in a diminished number of blood cells or total bone marrow loss. A number of metabolites appear to be involved in this process, and there may be several targets of toxicity, including stem, progenitor, and stromal cells.

Long-Term Exposures at Various Levels--From human evidence and supporting animal studies, the U.S. Department of Health and Human Services has determined that benzene is carcinogenic. Leukemia and subsequent death from cancer have occurred in some workers exposed to benzene for periods of less than 5 and up to 30 years. Long-term exposures to benzene may affect normal blood production, leading to anemia and internal bleeding. In addition, human and animal studies indicate that benzene is harmful to the immune system, increasing the chance for infections and perhaps lowering the body's defense against tumors. Exposure to benzene has also been linked with genetic mutations in humans and animals. Animal studies indicate that benzene has adverse effects on unborn animals. These effects include low birth weight, delayed bone formation, and bone marrow damage. Some of these effects occur at benzene levels as low as 10 parts of benzene per million parts of air.

Benzene can be measured in the blood and the breath. The body changes benzene to phenol, which can be measured in the urine. Amounts of benzene in blood samples and phenol in urine samples cannot be used to predict what degree of harmful health effects may occur. The US Environmental Protection Agency (EPA) set the maximum permissible level in drinking water at 5 parts of benzene per billion parts of water (ppb). Because benzene can cause leukemia, EPA established an ultimate goal of 0 ppb for benzene in drinking water and in ambient water such as rivers and lakes. The National Institute for Occupational Safety and Health (NIOSH) recommended an occupational exposure limit in air of 0.1 part of benzene per million parts of air (ppm). The Occupational Safety and Health Administration's (OSHA) legally enforceable limit is an average of 1.0 ppm over the standard 8-hour workday.

Polycyclic aromatic hydrocarbons (PAHs)

PAHs are a group of chemicals that are formed during the incomplete burning of coal, oil and gas, garbage, or other organic substances. PAHs can be man-made or occur naturally. There is no known use for most of these chemicals except for research purposes. A few of the PAHs are used in medicines and to make dyes, plastics, and pesticides. They are found throughout the environment in the air, water and soil. There are more than 100 different PAH compounds. Although the health effects of the individual PAHs vary, the following 15 PAHs are considered as a group with similar toxicity: acenaphthene, acenaphthylene, anthracene, benzanthracene, benzopyrene, benzofluoranthene, benzoperylene, benzofluoranthene, chrysene dibenzanthracene, fluoranthene, fluorene, indenopyrene, phenanthrene, pyrene.

Several factors will determine whether harmful health effects will occur and what the type and severity of those health effects will be. These factors include the dose (how much), the duration (how long), the route by which you are exposed (breathing, eating, drinking, or skin contact), the other chemicals to which you are exposed and your individual characteristics such as age, sex, nutritional status, family traits, life style, and state of health. As pure chemicals, PAHs generally exist as colorless, white, or pale yellow-green solids. Most PAHs are found as mixtures of two or more PAHs. They can occur in the air either attached to dust particles, or in soil or sediment as solids. They can also be found in substances such as crude oil, coal, coal tar pitch, creosote, road and roofing tar. Most PAHs do not dissolve easily in water, but some PAHs evaporate into the air. PAHs generally do not burn easily and they will last in the environment for months to years.

PAHs that are attached to dust and other particles in the air and originate from vehicle exhausts, asphalt roads, coal, coal tar, wildfires, agricultural burning and hazardous waste sites. Background levels of PAHs in the air are reported to be 0.02-1.2 milligrams per cublic meter (mg/m3) in rural areas and 0.15-19.3 mg/m3 in urban areas. You may be exposed to PAHs in soil near areas where coal, wood, gasoline, or other products have been burned or from the soil on or near hazardous waste sites, such as former manufactured-gas sites and wood-preserving facilities. PAHs have been found in some drinking water supplies in the United States. The background level of PAHs in drinking water ranges from 4 to 24 nanograms per liter . For most people, the greatest exposure to PAHs occurs in the workplace.

PAHs can enter the body through the lungs. PAHs enter the body quickly and easily by all routes of exposure. The rate at which PAHs enter your body is increased when they are present in oily mixtures and tend to be stored in the kidneys, liver, and fat, with smaller amounts in the spleen, adrenal glands and ovaries. Results from animal studies show that PAHs do not tend to be stored in for a long time and are excreted within a few days in the feces and urine.

The U.S. Department of Health and Human Services has determined that PAHs may be carcinogens. Several of the PAHs, including benzanthracene, benzopyrene, benzofluoranthene, benzofluoranthene, chrysene, dibenzanthracene, indenopyrene have caused tumors in laboratory animals when they ate them, when they were applied to their skin and when they breathed them in the air for long periods of time. Reports in humans show that individuals exposed by breathing or skin contact for long periods of time to mixtures of other compounds and PAHs can also develop cancer. Mice fed high levels of benzopyrene during pregnancy had difficulty reproducing and so did their offspring. The offspring from pregnant mice fed benzopyrene also showed other harmful effects, such as birth defects and decreased body weight. Similar effects could occur in humans, but we have no information to show that these effects do occur.

Studies in animals have also shown that PAHs can cause harmful effects on skin, body fluids, and the body's system for fighting disease after both short- and long-term exposure. These effects have not been reported in humans. PAHs are changed into chemicals that can attach to substances within the body. The presence of PAHs attached to these substances can then be measured in body tissues or blood after exposure to PAHs. However, this test is still being developed and it is not known yet how well it works. PAHs or their breakdown products can also be measured in urine. Although these tests can tell that you have been exposed to PAHs, it is not yet possible to use these tests to predict the severity of any health effects that might occur or to determine the extent of your exposure to the PAHs. These tests are not routinely available at a doctor's office because they require special equipment for sampling and detecting these chemicals.

Indoor Air Quality - Household Toxins      Automotive Exhaust Chemicals: Disease Causing Effects

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