What is secondhand tobacco smoke?

Secondhand tobacco smoke is the combination of the smoke given off by a burning tobacco product and the smoke exhaled by a smoker. It is also called environmental tobacco smoke, involuntary smoke, and passive smoke.

More than 7,000 chemicals have been identified in secondhand tobacco smoke. At least 69 of these chemicals are known to cause cancer, including arsenic, benzene, beryllium, chromium, and formaldehyde.

How are people exposed to secondhand smoke?

People can be exposed to secondhand smoke in homes, cars, the workplace, and public places. In the United States, the source of most secondhand smoke is from cigarettes, followed by pipes, cigars, and other tobacco products.

Which cancers are associated with secondhand smoke?

Inhaling secondhand smoke causes lung cancer in nonsmokers. Some research also suggests that secondhand smoke may increase the risk of breast cancer, nasal sinus cavity cancer, and nasopharyngeal cancer in adults and leukemia, lymphoma, and brain tumors in children, although more research is needed on this subject.

How can exposures to nonsmokers be reduced?

There is no safe level of exposure to secondhand smoke; even low levels of secondhand smoke can be harmful. In the United States, legislation has helped to reduce nonsmokers’ exposure to secondhand smoke. Federal law bans smoking on all domestic airline flights, nearly all flights between the United States and foreign destinations, interstate buses, and most trains. Smoking is also banned in most federally owned buildings.  Many state and local governments have also passed laws prohibiting smoking in public facilities, such as schools, hospitals, and airports, as well as private workplaces, including restaurants and bars.

Internationally, a growing number of nations require all workplaces, including bars and restaurants, to be smoke free.

Selected References:

• National Toxicology Program. Tobacco-Related Exposures, Report on Carcinogens, Fifteenth Edition. Triangle Park, NC: National Institute of Environmental Health and Safety, 2021. Also available online. Last accessed December 8, 2022.
• Office on Smoking and Health. About Secondhand Smoke. Atlanta, GA: U.S. Centers for Disease Control and Prevention, 2024. Available online. Last accessed June 13, 2024.
• U.S. Department of Health and Human Services. The Health Consequences of Involuntary Exposure to Tobacco Smoke: A Report of the Surgeon General. Rockville, MD: U.S. Department of Health and Human Services, Centers for Disease Control and Prevention, Coordinating Center for Health Promotion, National Center for Chronic Disease Prevention and Health Promotion, Office on Smoking and Health, 2006.
• U.S. Department of Health and Human Services. The Health Consequences of Smoking—50 Years of Progress: A Report of the Surgeon General. Atlanta: U.S. Department of Health and Human Services, Centers for Disease Control and Prevention, National Center for Chronic Disease Prevention and Health Promotion, Office on Smoking and Health, 2014.

What is soot?

Soot is a byproduct of the incomplete burning of organic (carbon-containing) materials, such as wood, fuel oil, plastics, and household refuse. The fine black or brown powder that makes up soot may contain a number of carcinogens, including arsenic, cadmium, and chromium.

How are people exposed to soot?

People may be exposed to soot by inhalation, ingestion, or absorption through the skin. Chimney sweeps likely have the highest occupational exposure to soot. Heating-unit service personnel, brick masons, building demolition personnel, horticulturists, and anyone who works where organic materials are burned may also be exposed through their work. The general public may be exposed through fireplaces, furnaces, engine exhaust, and particulate emissions from any combustion source.

Which cancers are associated with exposure to soot?

Exposure to soot was first associated with skin cancer of the scrotum among British chimney sweeps in 1775. Since then, many studies have found that chimney sweeps have an increased risk of scrotal and other skin cancers. Studies of chimney sweeps in several European countries have also found associations with other cancers, including lung, esophageal, and bladder cancers.

How can exposures be reduced?

In the United States, professional organizations for chimney sweeps keep members up to date on changing technology and safety issues.

Selected References:

• International Agency for Research on Cancer. Soot, As Found In Occupational Exposure of Chimney Sweeps, IARC Monographs on the Evaluation of Carcinogenic Risks to Humans, Volume 100F. Lyon, France: World Health Organization, 2012. Also available online. Last accessed June 10, 2024.
• National Toxicology Program. Soots, Report on Carcinogens, Fifteenth Edition. Triangle Park, NC: National Institute of Environmental Health and Safety, 2021. Also available online. Last accessed December 8, 2022.

What are strong inorganic acid mists containing sulfuric acid?

At room temperature, sulfuric acid is a clear, colorless, oily, corrosive liquid. Strong inorganic acid mists containing sulfuric acid may be generated during various manufacturing processes.

How are people exposed to strong inorganic acid mists containing sulfuric acid?

The major routes of occupational exposure are inhalation, ingestion, or absorption through the skin. Workers with potential exposure include those involved in manufacturing phosphate fertilizer, isopropanol, sulfuric acid, nitric acid, and lead batteries. Exposure may also occur during copper smelting, pickling (removing scale and oxides from metal surfaces), and other acid treatment of metals.

Which cancers are associated with exposure to strong inorganic acid mists containing sulfuric acid?

Occupational exposure to strong inorganic acid mists containing sulfuric acid is associated with increased risks of laryngeal and lung cancers.

How can exposures be reduced?

The U.S. Occupational Safety & Health Administration has information about exposure limits for sulfuric acid.

Selected References:

• International Agency for Research on Cancer. Mists from Strong Inorganic Acids, IARC Monographs on the Evaluation of Carcinogenic Risks to Humans, Volume 100F. Lyon, France: World Health Organization, 2012. Also available online. Last accessed June 11, 2024.
• International Agency for Research on Cancer. Summaries and Evaluations: Occupational Exposures to Mists and Vapours from Sulfuric Acid and Other Strong Inorganic Acids. Lyon, France: World Health Organization, 1997. Also available online. Last accessed February 20, 2019.
• National Toxicology Program. Strong Inorganic Acid Mists Containing Sulfuric Acid, Fifteenth Edition. Triangle Park, NC: National Institute of Environmental Health and Safety, 2021. Also available online. Last accessed December 8, 2022.

What is thorium?

Thorium is a naturally occurring radioactive metal that is found in soil, rock, and water. It is formed by the radioactive decay of uranium. Minerals such as monazite, thorite, and thorianite are rich in thorium and may be mined for the metal.

Thorium has coloring properties that have made it useful in ceramic glazes. Thorium also has been widely used in lantern mantles for the brightness it imparts (though alternatives are replacing it), and in welding rods, which burn better with small amounts of added thorium. Until the 1950s, thorium dioxide was used as a contrast agent (called Thorotrast) in medical radiology.

How are people exposed to thorium?

The primary ways people are exposed to thorium are inhalation, intravenous injection, ingestion, and absorption through the skin. More than 2.5 million people worldwide were exposed to thorium in Thorotrast between 1930 and 1950. Once injected, Thorotrast remains in the body, resulting in lifelong exposure to thorium.  

Although thorium is widespread in the environment, most people are not exposed to dangerous levels of the metal. However, people who live near thorium-mining areas or facilities that manufacture products with thorium may have increased exposure, especially if their water comes from a private well. Analytical laboratories can test water for thorium content.

Which cancers are associated with exposure to thorium?

Studies of patients who received intravascular injections of Thorotrast found an increased risk of liver tumors among these individuals. And there is research evidence that inhaling thorium dust increases the risk of lung and pancreatic cancer. Individuals exposed to thorium also have an increased risk of bone cancer because thorium may be stored in bone.

How can exposures be reduced?

Occasionally, household items may be found to contain thorium, such as some older ceramic wares in which uranium was used in the glaze, or gas lantern mantles. Although these exposures generally do not pose serious health risks, such household items should be retired from use to avoid unnecessary exposures. A radiation counter is required to confirm if ceramics contain thorium.

Selected References:

• Agency for Toxic Substances and Disease Registry. Toxic Substances Portal – Thorium. Atlanta, GA: Centers for Disease Control and Prevention, 2014. Available online. Last accessed June 11, 2024.
• Hedrick JB. U.S. Geological Survey Minerals Yearbook—2000: Thorium. Reston, VA: U.S. Geological Survey, 2000. Also available online. Last accessed February 20, 2019.
• National Toxicology Program. Ionizing Radiation, Report on Carcinogens, Fifteenth Edition. Triangle Park, NC: National Institute of Environmental Health and Safety, 2021. Also available online. Last accessed December 8, 2022.
• U.S. Environmental Protection Agency. Radiation Protection: Radionuclide Basics: Thorium. Washington, DC: U.S. Environmental Protection Agency, 2015. Available online. Last accessed February 20, 2019.

What is trichloroethylene?

Trichloroethylene (TCE) is a volatile, colorless liquid organic chemical. TCE does not occur naturally and is created by chemical synthesis. It is used primarily to make refrigerants and other hydrofluorocarbons and as a degreasing solvent for metal equipment. TCE is also used in some household products, such as cleaning wipes, aerosol cleaning products, tool cleaners, paint removers, spray adhesives, and carpet cleaners and spot removers. Commercial dry cleaners also use trichloroethylene as a spot remover.

How are people exposed to trichloroethylene?

TCE may be found in the air, water, and soil at places where it is produced or used. It breaks down slowly and remains in the environment for a long time. It readily passes through soil and can accumulate in groundwater.

People in the general population can be exposed to trichloroethylene by inhaling it in indoor and outdoor air, drinking contaminated water, or eating foods that have been washed or processed with contaminated water. Because this chemical was used extensively by the US military to degrease equipment, contaminated soil and groundwater can be found near many current and former military bases.

People who work with TCE may inhale the chemical from the air and absorb it through the skin.

Historically, TCE was used as a surgical anesthetic and inhaled analgesic. The Food and Drug Administration banned such use in the United States in 1977.

Which cancers are associated with exposure to trichloroethylene?

Prolonged or repeated exposure of trichloroethylene causes kidney cancer. Some evidence suggests that it may be associated with an increased risks of non-Hodgkin lymphoma and, possibly, liver cancer.

How can exposures be reduced?

People who work with or near TCE should wear protective equipment and minimize exposure to the chemical.

In general, people should avoid drinking water known to be contaminated with TCE, and children should be prevented from playing in areas where the chemical has been found in the soil. Always follow instructions on product labels to minimize exposure to hazardous chemicals such as TCE.

Selected References:

• Agency for Toxic Substances and Disease Registry (ATSDR). Toxicological Profile for Trichloroethylene (Update). U.S. Public Health Service, U.S. Department of Health and Human Services, Atlanta, GA. 2014. Also available online. Last accessed December 9, 2024.
• National Institute of Occupational Safety and Health. Trichloroethylene, NIOSH Pocket Guide to Chemical Hazards. Atlanta, GA: Centers for Disease Control and Prevention, 2010. Also available online. Last accessed December 9, 2024. 
• National Toxicology Program. 2021. Trichloroethylene, Report on Carcinogens, Fifteenth Edition.; Research Triangle Park, NC: U.S. Department of Health and Human Services, Public Health Service. Also available online. Last accessed December 9, 2024.

What are mineral oils?

The name mineral oil has been used to describe many colorless, odorless liquids. Most often, the term refers to a liquid by-product of the distillation of petroleum to produce gasoline and other petroleum-based products from crude oil. These oils, including lubricant base oils and products derived from them, are used in manufacturing, mining, construction, and other industries.

A complete description of mineral oils should include how the oils are refined. Oils used in cosmetic products are typically highly refined, whereas those used in automotive oils and fluids tend to be unrefined or only mildly treated. Highly refined products are not covered in this section.

How are people exposed to mineral oils?

Occupational exposure to mineral oils may occur among workers in various industries, including the manufacture of automobiles, airplanes, steel products, screws, pipes, and transformers. Workers in brass and aluminum production, engine repair, copper mining, and newspaper and commercial printing may also be exposed to mineral oils. The general population may be exposed to mineral oils that occur naturally or are present as environmental contaminants.

Which cancers are associated with exposure to mineral oils?

Exposure to mineral oils is strongly associated with an increased risk of nonmelanoma skin cancer, particularly of the scrotum.

How can exposures be reduced?

The U.S. Occupational Safety & Health Administration provides information about exposure limits to mineral oils.

Selected References:

• International Agency for Research on Cancer. Mineral Oils, Untreated or Mildly Treated, IARC Monographs on the Evaluation of Carcinogenic Risks to Humans, Volume 100F. Lyon, France: World Health Organization, 2012. Also available online. Last accessed May 3, 2024.
• National Institute of Occupational Safety and Health. Oil Mist (Mineral), NIOSH Pocket Guide to Chemical Hazards. Atlanta, GA: Centers for Disease Control and Prevention, 2010. Also available online. Last accessed February 15, 2019.
• National Toxicology Program. Mineral Oils: Untreated and Mildly Treated, Report on Carcinogens, Fifteenth Edition. Triangle Park, NC: National Institute of Environmental Health and Safety, 2021. Also available online. Last accessed December 5, 2022.

What are nickel and nickel compounds?

Nickel is a silvery-white metallic element found in the earth’s crust. It can be combined with other elements to form nickel compounds. Because of its unique properties, nickel has many industrial uses. Most nickel is used in metal alloys because it imparts useful properties, such as corrosion resistance, heat resistance, hardness, and strength.

How are people exposed to nickel and nickel compounds?

Occupational exposure is common in workplaces where nickel and nickel compounds are produced or used, including mining, smelting, welding, casting, and grinding. Occupational exposure to nickel occurs mainly through inhalation of dust particles and fumes or through skin contact.

The general population is exposed to low levels of nickel in air, water, food, and tobacco smoke. Nickel and its compounds get into the atmosphere through natural processes, such as the spread of dust and volcanic eruptions by the wind, as well as through industrial activities. The general public may also be exposed through nickel-plated materials, such as coins, jewelry, and stainless steel cooking and eating utensils.

Which cancers are associated with exposure to nickel and nickel compounds?

Exposure to various nickel compounds increases the risks of lung cancer and nasal cancer.

How can exposures be reduced?

Exposures of the general population to nickel compounds are almost always too low to be of concern. To protect workers, the U.S. Occupational Safety & Health Administration has issued exposure limits for nickel compounds.

Selected References:

• Health Effects Notebook for Hazardous Air Pollutants. Nickel Compounds. Washington, DC: U.S. Environmental Protection Agency, 2000. Available online. Last accessed February 15, 2019.
• International Agency for Research on Cancer. Nickel and Nickel Compounds, IARC Monographs on the Evaluation of Carcinogenic Risks to Humans, Volume 100C. Lyon, France: World Health Organization, 2012. Also available online. Last accessed June 10, 2024.
• National Institute of Occupational Safety and Health. Nickel Metal and Other Compounds (as Ni), NIOSH Pocket Guide to Chemical Hazards. Atlanta, GA: Centers for Disease Control and Prevention, 2010. Also available online. Last accessed February 15, 2019.
• National Toxicology Program. Nickel Compounds and Metallic Nickel, Report on Carcinogens, Fifteenth Edition. Triangle Park, NC: National Institute of Environmental Health and Safety, 2021. Also available online. Last accessed December 8, 2022.

What are indoor emissions from the household combustion of coal?

Burning coal inside the home for the purposes of heating or cooking produces particulate and gas emissions that may contain a number of harmful chemicals, such as benzene, carbon monoxide, formaldehyde, and polycyclic aromatic hydrocarbons.

How are people exposed to indoor emissions from the household combustion of coal?

People in some parts of the world, particularly in certain regions of China, have been exposed to indoor emissions from coal combustion through the use of unvented stoves and fire pits.

Which cancers are associated with exposure to indoor coal combustion emissions?

Lung cancer is associated with exposure to indoor coal combustion emissions.

How can exposures be reduced?

Installing indoor stoves with chimneys can reduce the level of indoor air pollution.

Selected References:

• International Agency for Research on Cancer.: Indoor Emissions from Household Combustion of Coal, IARC Monographs on the Evaluation of Carcinogenic Risks to Humans, Volume 100E. Lyon, France: World Health Organization, 2012. Also available online. Last accessed June 10, 2024.
• Lan Q, Chapman R, Schreinemachers DM, et al. Household stove improvement and risk of lung cancer in Xuanwei, China. Journal of the National Cancer Institute 2002; 94 (11): 826-835. [PubMed Abstract]. Also available online. Last accessed February 15, 2019.

What is chromium and what are hexavalent chromium compounds? 

Chromium is an odorless and tasteless metallic element that is found in the earth’s crust. It is also found in air, water, soil, and food.

Hexavalent chromium compounds are a group of chemicals that have useful properties, such as corrosion resistance, durability, and hardness. These compounds have been used widely as corrosion inhibitors and in the manufacture of pigments, metal finishing and chrome plating, stainless steel production, leather tanning, and wood preservatives. They have also been used in textile-dyeing processes, printing inks, drilling muds, fireworks, water treatment, and chemical synthesis.

How are people exposed to hexavalent chromium compounds?

Occupational exposure to hexavalent chromium can occur from inhalation of dusts, mists, or fumes containing hexavalent chromium, or from eye or skin contact. Industries with the largest number of workers exposed to high concentrations of airborne hexavalent chromium compounds include electroplating, welding, and chromate painting. 

Which cancers are associated with exposure to hexavalent chromium compounds?

Occupational exposure to these compounds is associated with increased risks of lung cancer and cancer of the paranasal sinuses and nasal cavity.

How can exposures be reduced?

The U.S. Occupational Safety & Health Administration has exposure limits and information about analytical methods used to evaluate hexavalent chromium exposure.

Selected References:

• Agency for Toxic Substances and Disease Registry: Chromium – ToxFAQs™. Atlanta, GA: Centers for Disease Control and Prevention, 2012. Also available online. Last accessed June 7, 2024.
• National Institute of Occupational Safety and Health. Hexavalent Chromium, Workplace Safety and Health Topics. Atlanta, GA: Centers for Disease Control and Prevention, 2013. Available online. Last accessed February 15, 2019.
• National Toxicology Program. Chromium Hexavalent Compounds, Report on Carcinogens, Fifteenth Edition. Triangle Park, NC: National Institute of Environmental Health and Safety, 2021. Also available online. Last accessed December 5, 2022.
• Occupational Safety and Health Administration. Hexavalent Chromium, Safety and Health Topics. Washington, DC: U.S. Department of Labor. Available online. Last accessed June 7, 2024.
• Office of Air Quality Planning and Standards. Methods to Develop Inhalation Cancer Risk Estimates for Chromium and Nickel Compounds. Research Triangle Park, NC: U.S. Environmental Protection Agency, 2011. Also available online. Last accessed July 3, 2024.

What is formaldehyde?

Formaldehyde is a colorless, strong-smelling, flammable chemical that is produced industrially and used in building materials such as particleboard, plywood, and other pressed-wood products. In addition, it is commonly used as a fungicide, germicide, and disinfectant, and as a preservative in mortuaries and medical laboratories. Formaldehyde also occurs naturally in the environment. It is produced during the decay of plant material in the soil and during normal chemical processes in most living organisms. It is also a combustion product found in tobacco smoke.

How are people exposed to formaldehyde?

People are exposed primarily by inhaling formaldehyde gas or vapor from the air or by absorbing liquids containing formaldehyde through the skin. Workers who produce formaldehyde or products that contain formaldehyde—as well as laboratory technicians, certain health care professionals, and mortuary employees—may be exposed to higher levels of formaldehyde than people in the general population.

The general public may be exposed to formaldehyde by breathing contaminated air from sources such as pressed-wood products, tobacco smoke, and automobile tailpipe emissions. Another potential source of exposure to formaldehyde is the use of unvented fuel-burning appliances, such as gas stoves, wood-burning stoves, and kerosene heaters.

Which cancers are associated with exposure to formaldehyde?

Studies of workers exposed to high levels of formaldehyde, such as industrial workers and embalmers, have found that formaldehyde causes myeloid leukemia and rare cancers, including cancers of the paranasal sinuses, nasal cavity, and nasopharynx.

How can exposures be reduced?

The U.S. Environmental Protection Agency recommends the use of “exterior-grade” pressed-wood products to limit formaldehyde exposure in the home. Formaldehyde levels in homes and work settings can also be reduced by ensuring adequate ventilation, moderate temperatures, and reduced humidity levels through the use of air conditioners and dehumidifiers.

Selected References:

• National Institute of Occupational Safety and Health. Formaldehyde, Workplace Safety and Health Topics. Atlanta, GA: Centers for Disease Control and Prevention. Available online. Last accessed August 6, 2024.
• National Toxicology Program. Formaldehyde, Report on Carcinogens, Fifteenth Edition. Triangle Park, NC: National Institute of Environmental Health and Safety, 2021. Also available online. Last accessed December 5, 2022.
• U.S. Environmental Protection Agency. Formaldehyde. Washington, DC: U.S. Environmental Protection Agency, 2013. Available online. Last accessed February 14, 2019.