1,4-dioxane has been used as a stabilizer for solvents, in particular 1,1,1- trichloroethane (TCA), and a solvent in its own right, as well as in a number of industrial and commercial applications (ATSDR, 2007; NTP, 2011).

The chemical causes cancer in laboratory animals and is reasonably anticipated to be a human carcinogen, first listed in the Annual Report on Carcinogens in 1981 (NTP, 2014).  In 1988, 1,4-dioxane was added to the list of chemicals known to the state to cause cancer [Title 27, California Code of Regulations, Section 27001].  It is also considered to pose a cancer risk by U.S.EPA (US EPA, 2010; 2013).

1,4-dioxane is an emerging contaminant.  In response to the occurrence data and potential adverse health effects, a notification level was established in accordance with Health and Safety Code section 116455.

In January 2019, the Division of Drinking Water (DDW) requested for the Office of Environmental Health Hazard Assessment (OEHHA) to establish a public health goal (PHG) for 1,4-dioxane. The PHG memo can be found here.

More information regarding State Water Board Actions on 1,4-Dioxane may be found on the 1,4-Dioxane Fact Sheet.

Notification Level

The drinking water notification level for 1,4-dioxane is 1 microgram per liter (μg/L). Certain requirements and recommendations apply to a water system if it serves its customers drinking water containing a contaminant greater than its notification level.  The response level, the level at which removal of the source from service, is 35 μg/L.

In 1998, the Drinking Water Program, now known as DDW, established a notification level 3 μg/L for 1,4 dioxane based on a US EPA (1990) drinking water concentration that corresponded to a 10-6 theoretical lifetime cancer risk.  In 2010, U.S. EPA revised its 1,4-dioxane risk evaluation, such that a 10-6 risk level corresponds to 0.35 μg/L (US EPA, 2010a, 2010b, 2013).  We revised its notification level to the 1-μg/L level in November 2010.

The notification level is slightly greater than the de minimis (1 X 10-6) level commonly used for notification levels based on cancer risk, reflecting difficulty in monitoring 1,4-dioxane at very low concentrations.

Analytical Methods

The recommended laboratory reporting limit for 1,4-dioxane is 1 μg/L, the same as the notification level. The reporting limit is similar to the detection limit for purposes of reporting, (DLR), which is established in regulation for chemicals with maximum contaminant levels. The DLR is the level at which the DDW is confident about quantification being reported.

DDW recommends that water systems' laboratories use the EPA Method 522 to analyze for presence of 1,4-dioxane in drinking water sources.

Findings in California Drinking Water

In 1998, we were notified about a 1,4-dioxane detection in a groundwater well; subsequently over the past decade, it has been found in a number of wells, mostly in southern California. In 2002, the presence of 1,4-dioxane in wastewater became problematic for a groundwater recharge project in southern California, prompting a need for additional water treatment.

Drinking water systems are not required by state regulations to monitor for 1,4-dioxane. Nevertheless, because of concerns about possible contamination, a number of systems have been directed by DDW to or have chosen to sample their supplies for 1,4-dioxane.

DDW's water quality database's reported findings of 1,4-dioxane from 2015 through 2018 are presented here (Excel). The water quality monitoring database is available here.

Detections included in the accompanying spreadsheet should not be considered to reflect 1,4-dioxane in drinking water served to customers, since water from the listed sources may be blended, treated, or not used to provide drinking water. For more information about specific drinking water supplies, see public water systems' annual Consumer Confidence Reports.


ATSDR, 2007, Toxicological Profile for 1,4-Dioxane (PDF), Agency for Toxic Substances and Disease Registry, Public Health Service, US Department of Health and Human Services.

NTP, 2014, 1,4-Dioxane, In Report on Carcinogens, 13th Edition; U.S. Department of Health and Human Services, Public Health Service, National Toxicology Program, page 176.

US EPA, 1990. 1,4-Dioxane. Integrated Risk Information System (IRIS), US Environmental Protection Agency, September 1.

US EPA, 2009. Emerging Contaminant--1,4-Dioxane Fact Sheet (PDF) , US EPA, Office of Solid Waste and Emergency Response, September.

US EPA, 2010a. 1,4-Dioxane, IRIS, US EPA, August 11.

US EPA, 2010b. Toxicological Review of 1,4-Dioxane, in Support of Summary Information on the Integrated Risk Information System (IRIS) , August.

US EPA, 2013. 1,4-Dioxane, IRIS, US EPA, September 20.