EPA evaluated 1,4-dioxane under the amended Toxic Substances Control Act (TSCA) and completed the final risk evaluation in December 2020. EPA will now begin the process of developing ways to address the unreasonable risks identified and has one year to propose and take public comments on any risk management actions.
Uses of 1,4-Dioxane
1,4-dioxane is currently used as a solvent in a variety of commercial and industrial applications such as in the manufacture of other chemicals, a processing aid, functional fluid, a laboratory chemical, in adhesives and sealants, in spray polyurethane foam, in printing inks, and as a dry film lubricant. 1,4-dioxane may be found as a contaminant in consumer products such as soaps and detergents. Information from the 2016 Chemical Data Reporting (CDR) for 1,4-dioxane indicates reported production volume in more than 1.1 million lbs/year (manufacture and import).
Risk Evaluation of 1,4-dioxane under Amended TSCA
In December 2020, EPA released the final risk evaluation for 1,4-dioxane. The final risk evaluation shows that there are unreasonable risks to workers and occupational non-users from 13 conditions of use. EPA found no unreasonable risks to the environment, consumers, bystanders, or the general population. As with any chemical product, EPA strongly recommends that users carefully follow all instructions on the product’s label.
In June 2019, EPA released the draft risk evaluation for 1,4-dioxane for public comment and peer review. In November 2020, EPA released a supplemental analysis to the draft risk evaluation which includes eight consumer uses where 1,4-dioxane is present as a byproduct, meaning when 1,4-dioxane is created from the breakdown of other chemicals. The supplemental analysis also assesses exposure to the general population from 1,4-dioxane in surface water.
In June 2017, EPA released the scope document for 1,4-dioxane which includes the hazards, exposures, conditions of use, and the potentially exposed or susceptible subpopulations EPA expects to consider in its risk evaluation of 1,4-dioxane conducted pursuant to TSCA section 6(b). In June 2018, EPA released the problem formulation for 1,4-dioxane which refined the scope of the 1,4-dioxane risk evaluation by clarifying the chemical uses that EPA expected to evaluate and describing how EPA expected to conduct the evaluation.
Treatment Technologies for 1,4-Dioxane
1,4-Dioxane is a solvent stabilizer frequently found at contaminated sites where methyl chloroform (1,1,1-trichloroethane) was used for degreasing. This report profiles the occurrence and properties of 1,4dioxane and provides a summary of the available remedial technologies. The information presented should prove useful to project managers and other regulatory officials who oversee cleanup of contaminated groundwater, particularly where chlorinated solvents are the principal contaminant. Consultants, including hydrogeologists, remediation engineers, and modelers, should also find this report useful, as should water utility operators and regulators. In recent years, the regulated community has become increasingly aware that 1,4-dioxane is likely to be present at sites where methyl chloroform is a contaminant.
Although 1,4-dioxane has been a constituent of methyl chloroform wastes for decades, recent improvements to analytical methods allowed its detection in the parts per billion range beginning in 1997. Analysis of 1,4-dioxane often must be specifically requested. The common practice of analyzing by a limited list of available methods for regulatory compliance has precluded detection of 1,4-dioxane. The properties that made 1,4-dioxane difficult to analyze in the past also make it difficult to treat. For example, 1,4-dioxane is fully miscible in water.
As a hydrophilic contaminant, it is not, therefore, amenable to the conventional ex situ treatment technologies used for chlorinated solvents. Successful remedial technologies must take into account the challenging chemical and physical properties unique to 1,4-dioxane. This report profiles technologies that have been shown to successfully remove or eliminate 1,4-dioxane and examines other technologies currently under development. 1,4-Dioxane is among the most mobile organic contaminants in the saturated zone. As a result, it may be found farther downgradient than the leading edge of a solvent plume.
The combination of a wider spatial occurrence and different requirements for treatment technologies make 1,4-dioxane a potentially problematic contaminant, particularly if it is discovered after site characterization and remedial design have already been completed. In some cases, discovery of 1,4-dioxane has necessitated expanded monitoring networks, larger capture zones, and the addition of new treatment technologies to the treatment train.
TREATMENT OF MEDIA CONTAINING DIOXANE
The physical and chemical properties of dioxane create challenges for removing this compound from water. Dioxane is well suited to removal by groundwater extraction because of its high solubility and low degree of partitioning to organic matter in soil.
However, the relatively low Henry’s Law constant of dioxane makes technologies such as air stripping generally ineffective in treating the chemical in water. Its low adsorptive capacity also limits the effectiveness of treatment by granular activated carbon (GAC), although one full-scale GAC application was identified. Bench-scale studies indicate that biodegradation of dioxane is possible, but information on field applications of this technology is limited (Dr. Basilis Stephanatos and others 2001). Technologies that are effective for treating chlorinated solvents are often ineffective for treating dioxane because the properties of dioxane differ from those of chlorinated solvents.
To date, the number and types of technologies available to treat dioxane are limited; however, research is under way to test and evaluate additional treatment technologies for this contaminant.
To date we are familiar with three technologies that have been used to treat dioxane at the pilot and full scale levels:
•Advanced oxidation (ex situ)
•Adsorption (GAC) (ex situ)
•Bioremediation
As discussed previously, dioxane in soil tends to readily partition to groundwater and does not sorb to soil particles. Therefore, groundwater is the primary medium of concern for this contaminant.