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1,4-Dioxane

Last Update: February 25, 2014

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, 2011).  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].  US EPA also considers it to pose a cancer risk (US EPA, 2010; 2013).

1,4-Dioxane is considered an emerging contaminant, and  in CDPH's draft regulations for groundwater replenishment using recycled water for indirect potable reuse, it's a chemical for which additional monitoring may be appropriate. 

Notification Level

CDPH has a drinking water notification level for 1,4-dioxane of 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 Department established its initial notification level at 3 µg/L, based on a US EPA (1990) drinking water concentration that corresponded to a 10-6 theoretical lifetime cancer risk. Later, in 2010, US EPA's 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).  CDPH 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 by CDPH 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 the level at which CDPH is confident about quantification being reported.the level at which CDPH is confident about quantification being reported.

The prior recommended reporting limit was 3 µg/L, which was equivalent to the previous notification level.  Some water systems were already using laboratories capable of measuring 1,4-dioxane at very low levels using Method 522Opens in new window. .  Some laboratories were also able to detect 1,4-dioxane at very low levels using hazardous waste Method 8270c. 

CDPH recommends that water systems' laboratories use the more sensitive analytical method to enable better characterization of the 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 CDPH to or have chosen to sample their supplies for 1,4-dioxane.  

The CDPH Drinking Water Program's water quality database's reported findings of 1,4-dioxane from 2000 through 2013 are presented here (Excel)Opens in new window..  A summary is presented in Table 1.  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.

 

Table 1. Drinking water sources and systems reporting a peak detection of 1,4-dioxane 
at or greater than 1 microgram per liter (through November 15, 2011)

County (ID Number)

Number 
of Sources

Number
of Systems

Peak
Concentration
(µg/L)

Los Angeles (19)

105

36

28.0

Monterey (27)

1

1

3.9

Orange (30)

28 13 26.7

TOTAL

134

50

-

For this table, we've used monitoring results reported to the CDPH Drinking Water Program and extracted from the water quality monitoring database.  "Sources" are those with two or more reported detections, and include active, standby, pending, inactive, and destroyed or abandoned sources; raw and treated drinking water wells and surface water sources; distribution systems; blending reservoirs; and other sampled entities.  We've not included data from some sources such as agricultural wells and monitoring wells. Where raw and treated samples or other results that indicate more than one sampling point for the same source (such as a well and its distribution system or blending reservoir), they are counted as coming from a single source. All reported detections, however, are included here (Excel)Opens new browser window.; non-detects are not included in the spreadsheet. 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.

NOTE:  These data should be considered draft, since they will change with subsequent updates.

References

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

NTP, 2011, 1,4-Dioxane (PDF)Opens in new window., In  Report on Carcinogens, 12th 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) Opens in new window., 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.

 
 
Last modified on: 2/25/2014 10:02 PM