Contaminant of the month: 1,4-dioxane

Feb. 3, 2014

Dioxane is a high volume industrial chemical with numerous uses.

What it is:

  • 1,4-dioxane is a synthetic organic chemical with many commercial uses. It is commonly called dioxane or para dioxane.
  • The molecular formula is C4H8O2. Molecular weight is 88.11 g/mole. Its structure is a six-membered saturated ring of four carbons and two oxygens. The arrangement is two O’s in the one and four positions in the ring and four CH2 groups in the two, three, five, six positions.
  • There are three different isomer dioxane molecules; the other two have oxygens in the one and two (1,2-dioxane) and one and three (1,3-dioxane) positions. Although isomers, they have different chemical and toxicological properties than 1,4-dioxane.
  • Dioxane is a high volume industrial chemical with numerous uses. In 1990 U.S. production was reported as between 10.5 million and 18.3 million pounds.
  • Dioxane is a flammable solvent and very soluble in water. It is very stable in the environment and not readily biodegraded or chemically degraded, so it is a persistent contaminant.
  • Among its uses are as a stabilizer for chlorinated hydrocarbons and as a solvent component of inks and adhesives.
  • It is a common contaminant in cosmetics and personal care products, including shampoos, deodorants, toothpaste and mouthwash.
  • Even though the names are similar, 1,4-dioxane is not related to dioxin (tetrachlorodibenzodioxin).


  • Because dioxane is very stable in the environment and very water soluble it is being found in water sources and drinking water supplies.
  • Because of its high boiling point (101.1o C) and high water solubility, it would be expected to be potentially in both surface and ground waters.
  • The U.S. Environmental Protection Agency (EPA) recently reported preliminary results from its Third Unregulated Contaminant Monitoring Rule survey. 1,4-dioxane was detected in the highest frequency of any of the 21 listed organic chemicals that were analyzed.
  • It was present in 188 of 988 public water supplies above the detection limit of 0.07 ppb. Six percent exceeded the reference concentration of 0.35 ppb; none exceeded 35 ppb.

Health effects:

  • Dioxane is a skin and inhalation irritant, and rats suffered liver and kidney damage from chronic exposure in drinking water.
  • Dioxane is considered a probable human carcinogen based upon liver and nasal cavity cancers in rats and mice in chronic tests conducted by the National Cancer Institute at 0.5 percent and one percent in drinking water.
  • The EPA calculated a projected lifetime cancer risks of 1/1,000,000 at 0.35 ppb, and 1/10/000 at 35 ppb.
  • Small epidemiological studies of exposed workers did not detect increased cancer incidences attributable to dioxane.


  • There are occupational exposure controls, but currently there is no EPA drinking water standard for dioxane. There is a Drinking Water Health Advisory at 35 ppb for a projected cancer risk of 1/10,000.
  • California has a Notification level of 1 ppb, and removal of the source from service is required at 35 ppb.
  • Dioxane is a likely candidate for future regulation.


  • Using EPA Method 522 California’s recommended reporting limit is 1 ppb or less using solid phase extraction, GC/MS with selected ion monitoring.
  • The MRL for the UCMR3 was 0.07 ppb.

Water treatment:

  • Due to its high water solubility, solvent properties and biological and chemical stability 1,4-dioxane is very difficult to remove from drinking water. Even granular activated carbon has limited effectiveness.
  • The most effective method for treatment of low concentrations is an advanced oxidation process using hydrogen peroxide and UV light, or ozone and UV light. These processes produce hydroxyl free radicals that are capable of extracting hydrogen from the molecule leading to its decomposition.
  • This process is being used in some wastewater reuse processes such as at the Orange County Water District in California.
  • Available point-of-use/point-of-entry offerings would be limited in effectiveness.

Dr. Joseph Cotruvo is president of Joseph Cotruvo and Associates, LLC, Water, Environment and Public Health Consultants. He is a former director of the U.S. EPA Drinking Water Standards Division.

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