Practical Perspectives of 1,4‐Dioxane Investigation and Remediation

Abstract

1,4‐Dioxane (dioxane) is a contaminant of emerging concern that is classified by the U.S. Environmental Protection Agency as a likely human carcinogen. Dioxane has been used as a minor or major ingredient in many applications, and is also generated as an unwanted by‐product of industrial processes associated with the manufacturing of polyethylene, nonionic surfactants, and many consumer products (cosmetics, laundry detergents, shampoos, etc.). Dioxane is also a known stabilizer of chlorinated solvents, particularly 1,1,1‐trichloroethane, and has been commonly found comingled with chlorinated solvent plumes. Dioxane plumes at chlorinated solvent sites can complicate site closure strategies, which to date have not typically focused on dioxane. Aggressive treatment technologies have greatly advanced and are clearly capable of achieving lower parts per billion cleanup criteria using ex situ advanced oxidation processes and sorption media. In situ chemical oxidation has also been demonstrated to effectively remediate dioxane and chlorinated solvents. Other in situ remedies, such as enhanced bioremediation, phytoremediation, and monitored natural attenuation, have been studied; however, their ability to achieve cleanup levels is still somewhat questionable and is limited by co‐occurring contaminants. This article summarizes and provides practical perspectives on dioxane analysis, plume stability relative to other contaminants, and the development of investigation tools and treatment technologies.

Trends in 1,4‐Dioxane Analyses: Implications for Identification and Characterization of Contaminated Groundwater Sites

“…The bias associated with semi‐volatile methods for 1,4‐dioxane (Chiang et al 2016) may have influenced the observed reporting limits for Method 8270 and Method 8270 SIM. However, the median reporting limits for the semi‐volatile methods are still more than an order of magnitude lower than those for Method 8260, which is much larger than any suspected bias.…”

“…Key constituents included 1,4‐dioxane, 1,1,1‐trichloroethane (1,1,1‐TCA), 1,1‐dichloroethane (1,1‐DCA), 1,1‐dichloroethene (1,1‐DCE), vinyl chloride (VC), cis‐1,2‐dichloroethene (cDCE), and trichloroethene (TCE). This list was intended to cover a number of contaminants that commonly co‐occur with 1,4‐dioxane when it is used an additive for industrial solvents (Anderson et al 2012; Adamson et al 2014: Chiang et al 2016), including intermediates in the degradation of both 1,1,1‐TCA and TCE (1,1‐DCE) as well as intermediates that are specific to TCE (cDCE, VC) and 1,1,1‐TCA (1,1‐DCA). For the period evaluated, a total of 822 discrete sites were identified where 1,4‐dioxane was analyzed in one or more locations during one or more event.…”

“…This has been exacerbated by varying application of methods available for analyzing 1,4‐dioxane in environmental samples. Because U.S. EPA Method 522, and its successor U.S. EPA 541, are approved only for drinking water, managers of contaminated sites in the United States generally choose between established methods such as U.S. EPA Method 8260 and U.S. EPA Method 8270 when analyzing for 1,4‐dioxane in groundwater (Chiang et al 2016). These methods have the distinct advantages of being widely available, relatively inexpensive, and capable of quantifying multiple different constituents in the same sample injection.…”

“…It is capable of lower reporting limits (below 1 part per billion) though it has also been shown to be biased low across various ranges of 1,4‐dioxane concentration (Chiang et al. 2016) due to low extraction efficiencies for this compound. Specifically, 1,4‐dioxane is water soluble and has a higher vapor pressure than many of the semi‐volatile compounds that are generally targeted by this method, meaning that the liquid/liquid extraction efficiency for 1,4‐dioxane can be poor.…”

“…There is an expectation that the use of Method 8270 and/or SIM‐based methods would improve our ability to “see” 1,4‐dioxane at sites, meaning that they would be options for prioritizing resources for monitoring and remediation of this pollutant. This is especially important when considering that the majority of 1,4‐dioxane sites are relatively dilute, with maximum historical concentrations generally in the low hundreds of μg per liter (Adamson et al 2014; Chiang et al 2016). However, there have been no comprehensive studies to‐date on how these analytical methods are being employed.…”