1,4-Dioxane is a volatile organic compound, classified as an ether. It is a colorless liquid with a faint sweet odor similar to that of diethyl ether. The compound is often called simply dioxane because the other dioxane isomers (1,2- and 1,3-) are rarely encountered.
Dioxane is used as a solvent for a variety of practical applications as well as in the laboratory, and also as a stabilizer for the transport of chlorinated hydrocarbons in aluminum containers. In 1985, the global production capacity for dioxane was between 11,000 and 14,000 tons. In 1990, the total U.S. production volume of dioxane was between 5,250 and 9,150 tons.
In the 1980s, most of the dioxane produced was used as a stabilizer for 1,1,1-trichloroethane for storage and transport in aluminium containers. Normally aluminium is protected by a passivating oxide layer, but when these layers are disturbed, the metallic aluminium reacts with trichloroethane to give aluminium trichloride, which in turn catalyses the dehydrohalogenation of the remaining trichloroethane to vinylidene chloride and hydrogen chloride. Dioxane "poisons" this catalysis reaction by forming an adduct with aluminum trichloride.
1,4-Dioxane in Tap Water
Most 1,4-dioxane contamination of drinking water comes from leaking underground storage tanks at hazardous waste sites, or discharges from manufacturing plants. Once it makes its way into sources of drinking water, 1,4-dioxane tends to stay there, because it does not break down easily. Because manufacturers don't have to report discharges of 1,4-dioxane, tracing contamination to its source is difficult. When a source is identified, the lack of enforceable standards means regulators have no legal grounds to stop contamination.
There is no federal maximum contaminant level set for 1,4-dioxane in drinking water. However, it has been included in the Contaminant Candidate List an ever-growing list of drinking water contaminants that are known or anticipated to occur in public water systems, which are not (yet) currently subject to EPA regulations.
1,4-Dioxane is a likely human carcinogen and has been found in groundwater at sites throughout the United States. The physical and chemical properties and behavior of 1,4-dioxane create challenges for its characterization and treatment. It is highly mobile and does not readily biodegrade in the environment.
Dioxane is classified by the National Toxicology Program as "reasonably anticipated to be a human carcinogen". It is also classified by the IARC as a Group 2B carcinogen: possibly carcinogenic to humans because it is a known carcinogen in other animals. The United States Environmental Protection Agency classifies dioxane as a probable human carcinogen (having observed an increased incidence of cancer in controlled animal studies, but not in epidemiological studies of workers using the compound), and a known irritant (with a no-observed-adverse-effects level of 400 milligrams per cubic meter) at concentrations significantly higher than those found in commercial products. Under California Proposition 65, dioxane is classified in the U.S. State of California to cause cancer. Animal studies in rats suggest that the greatest health risk is associated with inhalation of vapors in the pure form.
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