1,4-Dioxane

Historically, 90% of 1,4-Dioxane production was used as a stabilizer in chlorinated solvents such as 1,1,1-trichloroethane (TCA); however, use of 1,4-Dioxane has decreased since TCA was phased out by the Montreal Protocol in 1996 (USEPA 2017a). Current releases from this source are expected to be very low, but based on the number of vapor degreasers known to have used TCA, likely there are many sites where subsurface 1,4-Dioxane contamination has yet to be delineated (Adamson et al. 2014, Mohr et al. 2010). The full number of sites evaluated for 1,4-Dioxane is not known. Adamson et al. (2014) evaluated data from approximately 200 sites in California where 1,4-Dioxane was detected, but also reported that 1,4-Dioxane had yet to be included in sampling programs at several hundred more sites where its presence could be surmised based on the presence of specific chlorinated solvents and observed 1,4-Dioxane co-occurrence rates with these chlorinated solvents.

1,4-Dioxane is currently used in industrial processes and for industrial and commercial applications, which can include use as a processing aid and in functional fluids in closed systems. 1,4-Dioxane also is a common laboratory chemical reagent and is found in adhesives, sealants, dyes, pharmaceuticals, semiconductors, electronic components, photographic equipment, magnetic recording media, polymers, and plastics (USEPA 2017a). Based on data from the 2016 Chemical Data Reporting database, the current production volume is approximately 1 million pounds per year (USEPA 2016a). According to the Toxics Release Inventory for 2016, 55,732 pounds of 1,4-Dioxane were released to the air, 61,907 pounds to surface waters, 13,370 to onsite land disposal, and 486,124 pounds were transferred from the user to off-site disposal and other releases (USEPA 2016b).

The environmental fate of 1,4-Dioxane is characterized by partitioning to the atmosphere, surface water, and groundwater, and degradation by atmospheric oxidation or biodegradation. It is expected to be moderately persistent in the environment and have a low bioaccumulation potential (USEPA 2017a). Based on these characteristics and discharge routes, an evaluation of 1,4-Dioxane transport following a release may involve multiple media types.

1,4-Dioxane may be formed as a by-product of reactions based on condensing ethylene oxide or ethylene glycol during manufacture of detergents, shampoos, surfactants, some food additives (polysorbate 60 and polysorbate 80), and certain pharmaceuticals. The general population could be exposed to 1,4-Dioxane through contact with residues contained in these products. The presence of the compound has also been reported in other consumer products, such as adhesives and antifreeze. Small amounts may be present in foods (such as meats and tomato juice), which might indicate that it is a natural constituent of some foods. It is also present in tap water, which means that exposure through the ingestion of drinking water, bathing, showering, and other household water uses is possible (RoC 2014).

Although the mass of 1,4-Dioxane associated with solvent uses is many times greater than the 1,4-Dioxane mass associated with non-solvent uses, the other uses may contribute to the compound's occurrence in drinking water. Surface water sources are more likely to include 1,4-Dioxane from upstream wastewater effluent, while 1,4-Dioxane present in wastewater can filter into groundwater from landfills, septic systems, and leaking sewer lines (Mohr et al. 2010, Mohr 2017). Mohr (2017) observed that wastewater is unlikely to be a major source of 1,4-Dioxane in municipal supply wells, but domestic wells and small water systems might be more vulnerable to contamination from wastewater sources that contain 1,4-Dioxane.

EPA's Unregulated Contaminant Monitoring Rule (UCMR) is designed to collect chemical and microbiological occurrence data from all large and a representative group of small public water systems as part of a 5-year review cycle. The most recent round of testing, UCMR3 (2013-2015), required monitoring for 1,4-Dioxane along with 29 other contaminants. Over 36,000 drinking water samples were collected for 1,4-Dioxane and other contaminants suspected to be present in drinking water that lack health-based standards under the Safe Drinking Water Act. An initial assessment of the UCMR3 data by EPA (USEPA 2017b) noted that 1,4-Dioxane was found at or above the 10^-6 health-based reference level of 0.35 µg/L in 7% of the drinking water samples collected from monitored water systems. No sample results were above the 10^-4 health-based reference level of 35 µg/L.

1,4-Dioxane Drinking Water Occurrence Data from the Third Unregulated Contaminant Monitoring Rule
Adamson, D.T., E.A. Pina, A.E. Cartwright, S.R. Rauch, R.H. Anderson, T. Mohr, J.A. Connor.
Science of the Total Environment 596-597:236-245(2017) [Abstract]

Data collected from U.S. public drinking water supplies in support of the third round of the Unregulated Contaminant Monitoring Rule (UCMR3) were evaluated to assess the persistence of 1,4-Dioxane and the importance of groundwater contamination for potential exposure. The compound exceeded the EPA health-based reference concentration (0.35 µg/L) at 6.9% of these systems, and its detection was associated with detections of other chlorinated compounds, particularly 1,1-DCA, which is associated with the release of 1,4-Dioxane as a stabilizer for TCA. Data analysis suggested a decreasing trend in 1,4-Dioxane concentration and detection frequency over time.

Geohydrology, Water Quality, and Simulation of Ground-Water Flow in the Vicinity of a Former Waste-Oil Refinery near Westville, Indiana, 1997-2000
Duwelius, R., D. Yeskis, J. Wilson, and B. Robinson.
U.S. Geological Survey, Water-Resources Investigations Report 01-4221, 169 pp, 2002

Selected water-quality data and modeling information are presented in this report to describe water quality in relation to the site of the former refinery. A groundwater plume of 1,4-Dioxane at concentrations ranging from 3 to 31,000 µg/L extends to the southwest ~0.8 miles from the refinery site. 1,4-Dioxane levels in the surface water collected from the network of ditches surrounding the site range from 8 to 140 µg/L.

History of Use and Potential Sources: 1,4-Dioxane
Interstate Technology and Regulatory Council (ITRC), 5 pp, 2020

The Interstate Technology and Regulatory Council (ITRC) has developed a series of six fact sheets to summarize the latest science and emerging technologies regarding 1,4-Dioxane. The purpose of this fact sheet is to: review the history of 1,4-Dioxane manufacturing and usage; and provide an overview of the potential sources of releases of 1,4-Dioxane to the environment.

Implications of Matrix Diffusion on 1,4-Dioxane Persistence at Contaminated Groundwater Sites
Adamson, D.T., P.C. de Blanc, S.K. Farhat, and C.J. Newell. Science of the Total Environment 562:98-107(2016) [Abstract]

This study evaluated the extent to which 1,4-Dioxane's persistence was subject to diffusion of mass into and out of lower-permeability zones relative to co-released chlorinated solvents. Two release scenarios were evaluated within a 2-layer aquifer system using an analytical modeling approach. Overall results indicated that 1,4-Dioxane within transmissive portions of the source zone is depleted quickly due to characteristics that favor both diffusion-based storage and groundwater transport, leaving little mass to treat using conventional means. The results also highlight differences between 1,4-Dioxane and chlorinated solvent source zones, suggesting that back diffusion of dioxane mass might serve as a dominant long-term secondary source.

A Multi-Site Survey to Identify the Scale of the 1,4-Dioxane Problem at Contaminated Groundwater Sites
Adamson, D.T., S. Mahendra, K.L. Walker, S.R. Rauch, S. Sengupta, and C.J. Newell. Environmental Science & Technology Letters 1(5):254-258(2014) [Abstract]

In an evaluation of >2,000 sites in California where groundwater has been affected by chlorinated solvents, 1,4-Dioxane was detected at 194 of the sites, with 95% containing one or more chlorinated solvents. Although 1,4-Dioxane frequently co-occurs with TCA (76% of the study sites), no 1,4-Dioxane analyses were conducted at 332 (67%) of the TCA detection sites. Study results suggest that 1,4-Dioxane has not migrated beyond chlorinated solvent plumes and existing monitoring networks at the majority of sites, and that the primary risk is the large number of sites where 1,4-Dioxane likely is present but has not been identified.

Occurrence of 1,4-Dioxane in the Cape Fear River Watershed and Effectiveness of Water Treatment Options for 1,4-Dioxane Control
Knappe, D.R.U., C. Lopez-Velandia, Z. Hopkins, and M. Sun.
North Carolina State University, WRRI Project No. 14-06-U, UNC-WRRI-478, 97 pp, 2016

Based upon data collected between 2013 and 2015 as part of U.S. EPA's third unregulated contaminant monitoring rule (UCMR3), 7 of the 20 highest 1,4-Dioxane concentrations in U.S. drinking water occur in the Cape Fear River watershed of North Carolina. The overarching goal of this project is to gain insights into the occurrence of 1,4-Dioxane in surface water and drinking water in the Cape Fear watershed and to (1) identify sources of 1,4-Dioxane, (2) establish temporal and spatial variability of 1,4-Dioxane concentrations and mass flows, (3) determine the fate of 1,4-Dioxane in three surface-water treatment plants, (4) determine the effectiveness of ozonation and advanced oxidation processes for 1,4-Dioxane transformation in surface water, and (5) assess the effectiveness of point-of-use treatment devices for 1,4-Dioxane removal.

Regulatory Framework: 1,4-Dioxane
Interstate Technology and Regulatory Council (ITRC), 5 pp, 2020

The Interstate Technology and Regulatory Council (ITRC) has developed a series of six fact sheets to summarize the latest science and emerging technologies regarding 1,4-Dioxane. The purpose of this fact sheet is to: review the history of 1,4-Dioxane manufacturing and usage; and provide an overview of the potential sources of releases of 1,4-Dioxane to the environment.

Solvents Study
U.S. EPA, Office of Solid Waste, EPA 530-R-96-017, 52 pp, 1996

Undertaken as a result of a consent decree between EPA and the Environmental Defense Fund, this final report of the study on spent solvents discusses the wastes associated with the use of the materials as solvents, the toxicity of the wastes, and the management practices for the wastes. The chemicals addressed in this study are diethylamine, aniline, ethylene oxide, allyl chloride, 1,4-Dioxane, 1,1-dichloroethylene, and bromoform.

Tucson International Airport Area Superfund Site
Arizona Department of Environmental Quality.

The current contaminants of concern in site groundwater include TCE, DCE, chloroform, and chromium, plus 1,4-Dioxane in the Air Force Plant-44, Tucson Airport Remediation Project, and Airport Property areas. PCBs and metals contamination have also been found in some soils at the site. Additional information: USGS dioxane maps from 2017 and 2010, and a 2009 report.

Toxicological Profile for 1,4-Dioxane
Agency for Toxic Substances and Disease Registry (ATSDR), 295 pp, 2012

In addition to the toxicologic properties of 1,4-Dioxane, the profile includes chapters on chemical and physical information; production, import, use, and disposal; potential for human exposure (i.e., occurrence); and analytical methods.

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