Soots
Soots are dark, powdery deposits resulting from the incomplete combustion of carbon-rich organic fuels such as gasoline, diesel, coal, and wood. Composed mainly of elemental carbon, soots can also contain a range of harmful compounds, including sulfates, nitrates, and heavy metals like arsenic and cadmium. These complex mixtures vary based on their source and the conditions under which they were formed. Exposure to soots can occur through inhalation, ingestion, or skin contact, posing risks particularly to workers in industries such as construction, firefighting, and metallurgy.
Soots are classified as a known human carcinogen, linked to various types of cancer, including lung, bladder, and skin cancers. Historical observations, such as the identification of scrotal cancer in chimney sweeps in the 18th century, have prompted ongoing research into the health effects of soot exposure. Soots are also categorized under airborne particulate matter (PM), which the U.S. Environmental Protection Agency (EPA) regulates due to their adverse health impacts. Recent studies have reinforced concerns about their ability to penetrate deep into the lungs and cause DNA mutations. The EPA continues to monitor and strengthen air quality standards to mitigate the health risks associated with soot exposure.
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Soots
ROC STATUS: Known human carcinogen since 1980
ALSO KNOWN AS: Lampblack, carbon black
RELATED CANCERS: Scrotal and other skin cancers, lung cancer, leukemia, esophageal cancer, lymphatic and hematopoietic cancers, bladder cancer, prostate cancer
DEFINITION: Soots are dark, powdery deposits formed by the incomplete combustion of carbon-rich organic fuels, including gasoline and diesel fuel, coal, wood, fuel oil, paper, plastics, and household refuse. They are complex and variable mixtures of chemical compounds and differ depending on their source; soots from the same source can also differ depending on the conditions of their formation. Soots are composed primarily of elemental carbon. However, particles may also contain sulfates, ammonium, nitrates, condensed organic compounds, reactive gases, and heavy metals, such as arsenic, cadmium, and nickel.
Exposure routes: Inhalation, ingestion, dermal contact
Where found: Particulate emissions from any combustion source, including emissions from fireplaces and furnaces and exhaust from gasoline and diesel engines; chemical products such as pigments in paints and inks and in toners for xerography and laser printers; in the vulcanization process for rubber tires, imparting their typical black color
At risk: Workers cleaning home and industrial chimneys and boilers, brick masons, building demolition personnel, insulators, firefighters, metallurgical workers, horticulturists, people exposed to gasoline or diesel engine exhaust, and anyone present where organic material is burned
Etiology and symptoms of associated cancers: Compounds extracted from a number of soots cause mutations in standardized mutagenicity assays. Studies with laboratory animals demonstrated that soot from the same source produced skin tumors after dermal application. Soots are of concern when inhaled because their small size allows them to migrate deep into the lungs. Studies conducted in the 2020s confirmed the ability of toxic chemicals present in soot to penetrate deep into the lungs, causing mutations in DNA and leading to the development of cancerous cells.
History: Scrotal cancer was identified in chimney sweeps in 1775. Studies in Sweden, Denmark, Germany, and the United Kingdom later demonstrated a significantly increased risk of lung cancer among chimney sweeps. Research is ongoing to determine which components of soots and other small particles are responsible for their carcinogenicity and other health effects, such as respiratory illnesses.
Soots are in the general category of airborne particulate matter (PM). PM is classified as a criteria pollutant by the US Environmental Protection Agency (EPA), meaning that it is an air pollutant for which the EPA has established a national ambient air-quality standard. These pollutants are measured in air quality–control regions to determine whether the area meets federal air-quality standards. In 2024, the EPA strengthened its standards for soot and other PM, showing concern over its link to health conditions like cancer remained strong.
Bibliography
"EPA Finalizes Stronger Standards for Harmful Soot Pollution, Significantly Increasing Health and Clean Air Protections for Families, Workers, and Communities." Environmental Protection Agency, 7 Feb. 2024, www.epa.gov/newsreleases/epa-finalizes-stronger-standards-harmful-soot-pollution-significantly-increasing. Accessed 15 June 2024.
“Diesel Exhaust and Cancer Risk.” American Cancer Society, 26 Feb. 2024, www.cancer.org/cancer/risk-prevention/chemicals/diesel-exhaust-and-cancer.html. Accessed 15 June 2024.
Flinders University. "'Revolutionary' Research Discovers New Cause of Cancer Coming from Inside Us." ScienceDaily, 8 June 2023, www.sciencedaily.com/releases/2023/06/230608120903.htm.
International Agency for Research on Cancer. Chemical Agents and Related Occupations. Vol. 100-F. Lyon: International Agency for Research on Cancer, 2012.
“Lung Cancer Guide - What You Need to Know.” American Cancer Society, www.cancer.org/cancer/types/lung-cancer.html. Accessed 15 June 2024.
“Particulate Matter (PM) Pollution.” Environmental Protection Agency, 16 Apr. 2024, www.epa.gov/pm-pollution. Accessed 15 June 2024.
United States. Dept. of Health and Human Services, Public Health Service, National Toxicology Program. Thirteenth Report on Carcinogens. Research Triangle Park: Dept. of Health and Human Services, 2014.