Emerging contaminants are the subject of fervent research and discussion within environmental compliance circles. 1,4-dioxane, like other emerging contaminants, is currently being evaluated by regulatory agencies for further inclusion in environmental compliance regulations.
What is 1,4-dioxane?
1,4-dioxane is an industrial chemical used as a stabilizer for solvents and is also a by-product of surfactants used in many personal care products, like deodorants and shampoos. Toxicological data indicates that 1,4-dioxane is a probable human carcinogen, and the chemical has been detected in approximately 7% of public water supply drinking water samples in the United States. This detection rate is approximately 10 times that of detections of perfluorooctane sulfonate (PFOS) and perfluorooctanoic acid (PFOA) in the same dataset (USEPA UCMR3).
Because of its widespread use, 1,4-dioxane is typically found in groundwater at chlorinated solvent sites that have 1,1,1-TCA or TCE impacts and at unlined landfill sites. No maximum contaminant level (MCL) has yet been set for 1,4-dioxane by the United States Environmental Protection Agency (USEPA); however, a few state agencies have established state-specific concentration standards or guidance values.
What sets 1,4-dioxane apart...
1,4-dioxane has several properties that make it difficult to characterize and remediate. Here are a few of the challenges 1,4-dioxane presents:
- 1,4-dioxane mixes easily with water and does not tend to sorb (aka “stick”) to soil or volatilize into the air. Because of this, 1,4-dioxane has the potential to travel longer distances than established contaminants in groundwater, potentially forming large plumes. 1,4-dioxane’s high solubility also means that some traditional laboratory methods used to quantify other contaminants in groundwater do not work as well for this chemical.
- 1,4-dioxane cannot be removed from water by traditional remedial processes, like granular activated carbon (GAC) or air stripping.
- 1,4-dioxane has historically been considered resistant to biological degradation under both anaerobic and aerobic conditions.
Biological degradation of 1,4-dioxane – is it possible?
Recent research has found that under the right conditions, biological degradation of 1,4-dioxane can indeed occur. This is important because: a) it provides a way to manage 1,4-dioxane plumes under natural conditions; and b) biological remediation methods can be used to enhance 1,4-dioxane degradation. Monitored natural attenuation (MNA) and enhanced bioremediation can both be more cost-effective relative to other more intensive technologies, particularly for large plumes.
So, how is biological degradation done?
Researchers have identified a bacteria, called CB-1190, that can use 1,4-dioxane as a primary substrate (i.e., the CB-1190 bacteria can “eat” 1,4-dioxane). A few other bacteria have also been identified that can perform this function. There are now commercially available tests that can be performed to see if CB-1190 or similar bacteria are present at field sites. At sites where 1,4-dioxane consuming bacteria are already present in groundwater, 1,4-dioxane degradation may already be occurring, and may be enhanced by injection of oxygen or other nutrients. At sites where CB-1190 is not present, it can be added via bioaugmentation.
Additionally, other bacteria can be "tricked" into degrading 1,4-dioxane through the process of cometabolism. Cometabolism is a process in which bacteria consume another organic compound as substrate, and while doing so, create an enzyme that degrades 1,4-dioxane. Cometabolic biodegradation of 1,4-dioxane has been performed using propane injection to stimulate the process. Other co-substrates in addition to propane may also be effective.
Implementation of biodegradation enhancements at 1,4-dioxane sites
Existing site data, supplemented with additional testing, can help determine if 1,4-dioxane biodegradation is already occurring at a given site. These data can assist with assessing whether current conditions are adequate for 1,4-dioxane degradation, or if biostimulation (e.g., injection of oxygen or nutrients to stimulate native bacteria) or bioaugmentation (adding specialty bacteria) would enhance biodegradation effectiveness.
A note of caution
Because most traditional aboveground treatment technologies for pump & treat (P&T) systems (e.g., air stripping, GAC) do not treat 1,4-dioxane, active P&T systems may not be effective. Additionally, site practitioners may inadvertently increase the size of 1,4-dioxane plumes by re-injecting 1,4-dioxane along with treated groundwater. Supplemental treatment processes such as advanced oxidation processes (e.g., ozone and UV light) can treat 1,4-dioxane when used as part of P&T systems.
Find out more
Trihydro commonly works on several types of sites where 1,4-dioxane may be present, and has performed site characterization, data validation, technology screening, and remediation. We have implemented biostimulation (as well as phytoremediation and chemical oxidation) and are currently evaluating bioaugmentation as a potential remedy at field sites. If you are curious about 1,4-dioxane characterization and treatment, contact us or check out our on-demand 1,4-dioxane webinar where we sat down with Dr. Shaily Mahendra and Dr. Jens Blotevogel to discuss advances in 1,4-dioxane groundwater remediation.