1,4-Dioxane (1,4D) is a cyclic, aliphatic ether with the molecular formula of C4H8O2. 1,4D is a solvent that was used for a variety of practical applications/products (e.g., for inks, adhesives, paper, cotton, textile products, cosmetics, and shampoos). During the 1980s, 1,4D was used as a stabilizer for the transport of chlorinated solvents (1,1,1-trichloroethane) in aluminum containers, the material of choice for transporting bulk quantities of solvents. Its use as a stabilizer is environmentally significant, and 1,4D has been detected in groundwater at sites historically contaminated with chlorinated solvents. Since 1,4D is miscible in water, it is frequently found in groundwater plumes well before the chlorinated “parent” compound. Similarly, the concentration ratio of 1,4D to the chlorinated parent compound can be highly variable depending on a number of factors.
1,4D is classified by the National Toxicology Program as, “reasonably anticipated to be a human carcinogen.” It is also classified as a probable human carcinogen (Group B2) by the US EPA. Recent actions regarding 1,4D included the publishing of the third Unregulated Contaminant Monitoring Rule (UCMR 3) in 2012. UCMR 3 required analytical monitoring for 1,4D from 2013 to 2015 using US EPA Method 522 (a gas chromatography/mass spectrometry [GC/MS] method for drinking water), which specifies a minimum reporting limit of 70 ppt. Increasingly, 1,4D has also been appearing in state and federal guidance for air pollution control and release reporting and in water pollutant control and National Pollutant Discharge Elimination System (NPDES) permitting. From a remedial standpoint, 1,4D does not respond to treatment methods like air stripping or granular activated carbon, and it is highly resistant to biodegradation in the subsurface.
From an analytical standpoint, the analysis of 1,4D in environmental samples is a challenge in one sense and versatile in another. 1,4D has been analyzed in groundwater monitoring events nationwide as a volatile organic at some sites, using US EPA SW-846 Method 8260 [either using full-scan mode or selective ion monitoring (SIM)]; however, because 1,4D is water miscible and does not purge well, laboratory quality control (QC) recoveries of 50 – 60% are common. 1,4D has also been analyzed at other sites as a semivolatile organic using SW-846 Method 8270 (using full-scan mode SIM); however, as 1,4D is a “light” semivolatile, losses occur during the extraction/concentration process and similar laboratory QC recoveries (40 – 60%) are also routine. Improvements in 1,4D recoveries, mean more accurate (viz., higher) reported concentrations of 1,4D are being observed in groundwater samples collected at sites nationwide, through the recent laboratory use of an isotope dilution (IS) technique. The IS technique utilizes a synthetically manufactured, 1,4-dioxane-d8 (1,4Dd8) compound for much improved quantitation. The use of 1,4Dd8, which is added to samples by the laboratory immediately prior to preparation and analysis, improves the accuracy of the analysis for 1,4D since the IS technique recovery corrects the concentration of 1,4D. To explain the recovery-correction concept, in a very rudimentary manner, if the raw laboratory 1,4D sample result is 1.5 µg/L and the laboratory QC recovery is 50%, then the recovery-corrected result is multiplied by 2 for a final 1,4D reported result of 3.0 µg/L. Regarding the use of the UCRM 3-specified US EPA Method 522 for 1,4D analysis, some commercial laboratories follow the method as written, and others have modified the method to include the 1,4Dd8 IS recovery correction for accuracy improvement.
Selecting the correct laboratory and specifying the appropriate 1,4D analysis method involves careful planning and site-specific considerations. In our 30th year, the Environmental Standards senior chemistry staff can assist in advising on laboratories and methods, as well as preparing analytical plans, auditing laboratories being considered, and/or conducting the critical third-party data validation.