1,4-Dioxane

1,4-Dioxane is a volatile organic compound that is completely miscible in water. The very low log K_ow and measured K_oc values suggest that 1,4-Dioxane will be mobile in soils. Volatilization of 1,4-Dioxane from moist soil surfaces is expected to be an important fate process given its Henry's Law constant. 1,4-Dioxane also is expected to volatilize from dry soil surfaces based upon its vapor pressure. While the Henry's Law constant for 1,4-Dioxane is relatively low compared to many co-occurring VOCs, it increases significantly with temperature. 1,4-Dioxane also forms an azeotropic mixture with water (HSDB 2015*).

Chemical Abstracts Service (CAS) number	123-91-1
Physical description (physical state at room temperature)	Clear, flammable liquid with a faint, pleasant odor
Molecular weight (g/mol)	88.106
Water solubility	Miscible
Melting point (°C)	11.75
Boiling point (°C) at 760 mm Hg	101.2
Vapor pressure at 25°C (mm Hg)	38.1
Specific gravity at 20°C	1.0337
Octanol-water partition coefficient (log Kow)	-0.27
Measured Koc values	17 and 29
Henry's law constant at 25°C (atm-m3/mol)	4.8 X 10-6

Abbreviations: g/mol — grams per mole; °C — degrees Celsius; mm Hg — millimeters of mercury; atm-m3/mol — atmosphere-cubic meters per mole

Based upon the K_oc values, 1,4-Dioxane is not expected to adsorb to suspended solids and sediment if released into water. At actual solvent release sites, 1,4-Dioxane has the potential to migrate considerably farther in groundwater than co-occurring chlorinated solvents such as 1,1,1-trichloroethane (TCA) or TCA breakdown products due to its high solubility and low affinity for sorption to soil organic matter (Mohr 2001).

Although 1,4-Dioxane is relatively recalcitrant to degradation under ambient subsurface conditions, its natural attenuation at field sites has been documented (Adamson et al. 2015, Gedalanga et al. 2016), and the 1,4-Dioxane degradation pathway for several strains of Pseudonocardia has been mapped (Stevenson and Turnbull 2017). Field and laboratory results show that aerobic conditions favor 1,4-Dioxane degradation, but the presence of chlorinated solvents and metals may have an inhibiting effect (Adamson et al. 2015, Zhang et al. 2016). When released to the air, 1,4-Dioxane is photooxidized by hydroxyl radicals with an estimated half life of 33 hours (HSDB 2015).

The searchable PubChem database offers additional peer-reviewed information on the chemical and physical properties of 1,4-Dioxane as well as summaries of literature on its environmental fate, behavior, and human health effects.

* All of the information in the first paragraph and the properties in the table come from the Hazardous Substances Data Bank page for 1,4-Dioxane.

1,4-Dioxane: Priority Existing Chemical No. 7
NICNAS (National Industrial Chemicals Notification and Assessment Scheme), National Occupational Health and Safety Commission, Commonwealth of Australia, Canberra, ACT. 129 pp, 1998

This report discusses 1,4-Dioxane chemistry, manufacture and use, environmental behavior, occupational exposure, and toxicity.

Behavior of 1,4-Dioxane in the River in Tokyo
Nishino, T., M. Ohno, Y. Sasaki, K. Isobe, H. Kanegae, O. Murakami, N. Suzuki, O. Nakasugi.
Journal of Environmental Chemistry 18(3):333-340(2008) [Open Access]

The objective of the study was to assess the concentrations of 1,4-Dioxane at several locations along the Tama River. The study found that levels of 1,4-Dioxane increased along river branches, especially those carrying effluent from upgradient sewage treatment plants. The respective contribution rates of the loads of the branches and the sewage were estimated as 25% and 75%. The measured load of inflow was 30 times higher than the estimated loads based on the pollutant release-and-transfer register system in the river basin. These findings suggest that the present register system has never covered the dioxane emission sources completely.

Effect of 1,4-Dioxane on the Expansion of Montmorillonite Layers in Montmorillonite/Water Systems
Wu, J., P.F. Low, and C.B. Roth.
Clay and Clay Minerals 42(2):109-113(1994)

In a late 1980s study of how simple organic molecules interact with montmorillonite, a common clay mineral, 1,4-Dioxane was the only neutral organic molecule of those tested that had a significant effect on the swelling and flocculation of the montmorillonite. Because swelling and flocculation can have a profound influence on the permeability of a soil (and, thereby, on diffusive and convective transport within it), this present study was conducted to determine how dioxane affects the interlayer distance in montmorillonite.

Environmental Fate, Transport, and Investigation Strategies: 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: describe how the physical and chemical properties of 1,4-Dioxane affect the primary processes relevant for behavior and movement of 1,4-Dioxane in the environment; provide a helpful framework for developing a site conceptual model for 1,4-Dioxane; and highlight how an effective investigation into the distribution of 1,4-Dioxane in the environment might differ from an investigation for its common co-contaminants.

Fate of 1,4-Dioxane in the Aquatic Environment: From Sewage to Drinking Water
Stepien, D.K., P. Diehl, J. Helm, A. Thoms, and W. Puettmann.
Water Research 48:406-419(2014) [Abstract]

A study of the occurrence and transport of 1,4-Dioxane in the aquatic environment in Germany and Poland examined the mobility of dioxane from wastewater to surface water, bank filtered groundwater, and finally to public water supply plants. Additional information: Stepian dissertation, Chapter 4

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.

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