Emerging Contaminants: 1,4-dioxane

1,4-Dioxane is a semi-volatile, colorless liquid with a mild ethereal odor, also known as diethylene dioxide, dioxane, or p-dioxane. It is miscible with water, oils and most chlorinated solvents. It is also flammable and, during storage, may form explosive peroxides.

Sources of 1,4-Dioxane

1,4-Dioxane is primarily used as a stabilizer in chlorinated solvents. At one time, approximately 90% of the 1,4-dioxane produced went into the production of 1,1,1-trichloroethane (TCA). This application has now been phased out due to TCA’s destructive effects on atmospheric ozone. Industries or processes in which 1,4-dioxane is used, or is associated, include:

  • Chlorinated solvents manufacturing (as a stabilizer)
  • Organic chemical manufacturing
  • Textile processing
  • Paper manufacturing
  • Varnish stripper and paint production
  • Pesticide production

When released into the air, 1,4-dioxane degrades relatively quickly through reactions with photochemically-produced hydroxyl radicals. However, degradation in water and soil is slow. For this reason, 1,4-dioxane is persistent in the environment, and will remain present in areas of groundwater contamination. Due to the ubiquitous nature of 1,4-dioxane, contamination can be found in many parts of the U.S.

A Probable Carcinogen

The United States Environmental Protection Agency’s (USEPA) Integrated Risk Information System (IRIS) released a toxicological review of the contaminant to include a cancer assessment. IRIS designated 1,4-dioxane as “likely to be carcinogenic to humans”. In addition, the IRIS system indicated that 1,4-dioxane concentrations of 0.35 ppb (ug/ L) or higher in drinking water would result in 1 in 1,000,000 people developing cancer. In animal testing, 1,4-dioxane increased the incidence of cancer in the liver, lungs, gall bladder, and on the skin.

Non-carcinogenic side effects of 1,4-dioxane include liver and kidney toxicity. The primary routes of human exposure to 1,4-dioxane are inhalation, ingestion, and dermal contact.

Occurrence in The U.S.

The USEPA included 1,4-dioxane on its third Unregulated Contaminant Monitoring Rule (UCMR 3) for drinking water contaminants. Levels of 1,4-dioxane were monitored at 800 water treatment plants across the U.S. between 2013 and 2015.

Chemical Name 1,4 - Dioxane
Chemical FormulaC4H8O2
Molecular Weight88.12
Water SolubilityHighly Soluble
Density 1.033 g/mL

Results of the UCMR 3 initiative shows that over 20% of treatment plants tested had at least one sample measure above the USEPA established reporting limit concentration of 0.07 ppb. In addition, over 7% of sites had at least one sample measure above the 0.35 ppb 1 in 1,000,000 cancer risk limit.

Figure 1 provides a detailed heat map showing the occurrence of 1,4-dioxane samples testing above the 0.07 ppb reporting limit across the U.S. The data shows expectedly high concentrations in highly industrialized regions.

Heat Map Showing 1,4-Dioxane Occurrence from UCMR3. Reporting Limit = 0.07 ppb
Figure 1: Heat Map Showing 1,4-Dioxane Occurrence from UCMR 3. Reporting Limit = 0.07 ppb.


UV Light Key to Treatment Process

1,4-Dioxane’s low vapor pressure and high solubility render air stripping, carbon adsorption and reverse osmosis ineffective for its removal.

However, UV-oxidation using UV light and hydrogen peroxide is effective at breaking down 1,4-dioxane. The irradiation of hydrogen peroxide by UV light generates hydroxyl radicals. These radicals effectively oxidize 1,4-dioxane, breaking it down into non-toxic molecular components.

Extensive UV Installations

Trojan Technologies has conducted numerous pilot studies to verify the efficacy of 1,4-dioxane reduction using UV light and hydrogen peroxide. Currently, Trojan has dozens of surface and groundwater UV-oxidation installations designed for its removal. Collectively, these installations treat over 380 million gallons of water each day.

TrojanUVPhox installation in Tucson, Arizona
TrojanUVPhox system treating 1,4-dioxane in Arizona.

Treating Multiple Contaminants With One UV System

As an added benefit to 1,4-dioxane treatment, TrojanUV’s UV- oxidation systems also provide up to 6-log removal of microorganisms including Cryptosporidium, Giardia, and microbes including adenovirus and treat for other chemical contaminants including N-nitrosodimethylamine (NDMA), endocrine disruptor compounds, pesticides, volatile organic compounds (VOCs), and taste- and odor-causing compounds such as MIB and geosmin.


National Toxicology Program: 12th Report on Carcinogens, 2011; EPA Toxic Release Inventory, 2009; EPA Integrated Risk Information System (IRIS); USEPA Unregulated Contaminant Monitoring Rule 3 Occurrence Data, 2017