Today we are taking a look at 1,4-dioxane, which, like other emerging contaminants, is currently being evaluated by regulatory agencies for further inclusion in environmental compliance regulations. EPA included 1,4-dioxane in its December 2016 list of top 10 chemicals to be reviewed under the ongoing Toxic Substances Control Act reform. Let’s find out more.
What sets 1,4-dioxane apart...
A BIT OF BACKGROUND
Emerging contaminants are defined as “any synthetic or naturally occurring chemical or any microorganism that is not commonly monitored in the environment but has the potential to enter the environment and cause known or suspected adverse ecological and/or human health effects”. (Source: USGS)
What is 1,4 dioxane?
1,4-dioxane is an industrial chemical that is 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 (Source: USEPA).
Because of its widespread use, 1,4-dioxane is typically found 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 EPA; however, a few state agencies have established state-specific concentration standards or guidance values.
1,4-dioxane has several unique properties that make it difficult to characterize and remediate. Here are a few of the hurdles:
Biological degradation of 1,4-dioxane – is it possible?
- 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. The high solubility of this chemical also means that some traditional laboratory methods used to quantify other contaminants in groundwater don’t work as well for 1,4-dioxane.
- 1,4-dioxane can’t be removed from water by traditional remedial treatment processes, like granular activated carbon (GAC) or air stripping.
- 1,4-dioxane has been considered resistant to biological degradation under both anaerobic and aerobic conditions.
Let’s focus on this last hurdle: the possibility of biological degradation of 1,4-dioxane. 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 reduce 1,4-dioxane plumes under natural conditions; and b) it means there may be effective biological remediation methods that can be used to enhance the degradation of 1,4-dioxane. We are typically encouraged by these two methods (monitored natural attenuation and enhanced bioremediation) because they can both be a more cost-effective remediation method relative to other more intensive technologies, particularly for large plumes.
So, how is it done?
Researchers recently identified a bacteria, called “CB-1190”, that is capable of using 1,4-dioxane as a primary substrate, i.e. the CB-1190 bacteria can “eat” 1,4-dioxane. There are now commercially available tests that can be performed to see if CB-1190 is present at field sites. At sites where it is 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 isn’t present, it could be added via bioaugmentation.
Implementation of biodegradation enhancements at 1,4-dioxane sites
Existing site data, supplemented with additional testing, can help you find out if biodegradation is already occurring at a given site. With these data, you can assess 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 WARNING
Because most traditional aboveground treatment technologies for pump-and-treat systems (e.g., air stripping, GAC) do not treat 1,4-dioxane, active pump-and-treat 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. Advanced oxidation processes (e.g. ozone and UV light) can treat 1,4-dioxane when used as part of pump-and-treat 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, and remediation technology screening and implementation at many of these sites. We have implemented biostimulation and are currently evaluating bioaugmentation as a potential remedy at field sites. If you are curious about characterization and treatment of emerging contaminants like 1,4-dioxane, please contact Fritz Krembs, P.E, P.G.
, Senior Engineer and Geologist.