Coal tar

Coal tar is a brown or black liquid of extremely high viscosity. Coal tar is among the by-products when coal is carbonized to make coke or gasified to make coal gas. Coal tars are complex and variable mixtures of phenols, polycyclic aromatic hydrocarbons (PAHs), and heterocyclic compounds.

Applications

Pavement Sealcoat

Coal tar is incorporated into some parking-lot sealcoat products, used to protect and beautify the underlying pavement.‍ Sealcoat products that are coal-tar based typically contain 20 to 35 percent coal-tar pitch. Substantial concerns have been raised about the safety of this application of coal tar, given that coal tar is known to cause cancer in humans and that several PAH compounds in coal tar are toxic to aquatic life. Defenders of coal-tar use in sealcoat have pointed out that humans are exposed to PAHs through many pathways, and similarly that the urban environment has many potential sources of PAHs.‍

The primary use of coal tar based sealcoats is regional within the US but federal research shows it is used in states from Alaska to Florida and several areas have banned its use in sealcoat products including: The District of Columbia; the City of Austin, Texas; Dane County, Wisconsin; Washington State; and several municipalities in Minnesota.

Industrial

Being flammable, coal tar is sometimes used for heating or to fire boilers. Like most heavy oils, it must be heated before it will flow easily.

Coal tar was a component of the first sealed roads. In its original development by Edgar Purnell Hooley, tarmac was tar covered with granite chips. Later the filler used was industrial slag. Today, petroleum derived binders and sealers are more commonly used. These sealers are used to extend the life and reduce maintenance cost associated with asphalt pavements, primarily in asphalt road paving, car parks and walkways.

A large part of the binders used in the graphite industry for making "Green Blocks" are Coke Oven Volatiles or COV. A considerable portion of these COV used as binders is coal tar. During the baking process of the green blocks as a part of commercial graphite production, most of the coal tar binders are vaporised and are generally burned in an incinerator to prevent release into the atmosphere, as COV and coal tar can be injurious to health.

Coal tar is also used to manufacture paints, synthetic dyes, and photographic materials.

Medical

Also known as liquor carbonis detergens (LCD), and liquor picis carbonis (LPC) it can be used in medicated shampoo, Wrights Coal Tar Soap, and ointment, as a treatment for dandruff and psoriasis, as well as being used to kill and repel head lice. When used as a medication in the United States, coal tar preparations are considered over-the-counter drug pharmaceuticals and are subject to regulation by the United States Food and Drug Administration. Named brands include Denorex, Balnetar, Psoriasin, Tegrin, T/Gel, and Neutar. When used in the extemporaneous preparation of topical medications, it is supplied in the form of Coal Tar Topical Solution United States Pharmacopeia, which consists of a 20% percentage solution of coal tar in alcohol, with an additional 5% w/v of polysorbate 80; this must then be diluted in an ointment base such as petrolatum.)

Safety

According to the International Agency for Research on Cancer, preparations that include more than five percent of crude coal tar are on their List of IARC Group 1 carcinogens.

In 40 urban lakes nationwide, scientists with the U.S. Geological Survey (USGS) found coal tar sealants account for about half of hazardous chemicals known as polycyclic aromatic hydrocarbons, or PAHs, while vehicle-related sources such as motor oil account for one-fourth. A 2013 Mahler and Baylor University study calculated that lifetime exposure to PAHs, via house dust, was 38 times higher for people living near coal-tar-sealed pavement than those who weren't. PAHs are toxic to mammals, birds, fish, frogs and plants, and seven are suspected human carcinogens.

Resources

Related GEM.wiki articles

• Coal slurry impoundment
• International coal combustion waste news stories
• TVA Kingston Fossil Plant coal ash spill
• TVA Widows Creek coal waste spill
• Massey Energy
• Federal coal subsidies
• Estimating U.S. Government Subsidies to Energy Sources 2002-2008
• State coal subsidies
• Health effects of coal
• Mercury and coal
• Heavy metals and coal
• Sulfur dioxide and coal
• Environmental impacts of coal
• Air pollution from coal-fired power plants
• Coal sludge
• Fly ash
• United States and coal

External links

• Coal Tar Free America