In a never-ending list of chemical pollutants, a compound that is gaining a lot of attention is 1,4-dioxane. In fact, New Jersey just became the first state to set regulations on the quantity of 1,4-dioxane that can be present in drinking water.
1,4-dioxane, commonly called dioxane (the other two isomers – 1,2-dioxane and 1,3-dioxane are rarely ever seen), is an ether with the molecular formula of C4H8O2. Dioxane was previously used as a polar aprotic solvent. For those who remember their organic chemistry from college, SN2 reactions involve the use of polar aprotic solvents. Since its original use in laboratories, dioxane has been determined to be carcinogenic and, unlike many organic pollutants, it is completely soluble in water. Dioxane’s use as a solvent for industrial purposes has been mostly replaced with tetrahydrofuran, which has a higher boiling point and a lower toxicity. However, the story does not end there!
The Environmental Working Group (EWG) recently examined over 25,000 commercially available cosmetics products, and found that approximately 22% of them contained a measurable amount of 1,4-dioxane. While this is an alarming statistic, what’s even more alarming is that 1,4-dioxane will not appear as one of the listed ingredients. Unfortunately, that means you’ll have to do a little bit of digging to determine whether the product contains this contaminant. Dioxane is actually a byproduct of a process called ethoxylation and it is commonly seen in cosmetics that use sodium laureth sulfate (the suffix “eth” stands for ethoxylate). The ethoxylated product is much gentler on skin than the original sodium laurel sulfate, which makes it beneficial to both the manufacturer and the product’s end user.
1,4-dioxane is also a byproduct in the manufacturing of detergents, foaming agent and emulsifiers. A few examples of these compounds are polyethylene glycol (PEG) and any compound containing the suffixes or prefixes “eth”, “oxynol”, “ceteareth” or “oleth.” In the study done by the EWG, 97% of hair relaxers and 57% of baby soaps contained a detectable amount of 1,4-dioxane. This prevalence became such an issue that the U.S. Food & Drug Administration (USFDA) had to step in and create guidelines on how much 1,4-dioxane can be present in cosmetic products. They set the maximum allowable limit at 10 ppm (mg/L). Between 1981 and 1997 the quantity of 1,4-dioxane in cosmetic products ranged from 2-279 ppm. In 2018, only 2 of the 82 randomly tested products contained over 10 ppm. It appears that the FDA’s plan is working.
Now, let’s think about this from an environmental point of view. 1,4-dioxane is a highly water soluble chemical that is found in personal care products, which means they end up going down our drains and finding their way into our drinking water. To avoid consuming dangerous levels of this contaminant, there need to be trace levels of 1,4-dioxane in our water sources. The EPA was thinking along these lines when it established EPA method 522 for the quantitation of 1,4-dioxane in drinking water by GC/MS. Since then, 1,4-dioxane has been listed on the Unregulated Contaminant Monitoring Rule (UCMR) list which means that the analytical community has put a premium on quantifying it. Unfortunately, this is a rather tricky analyte to recover in a drinking water matrix. 1,4-dioxane is commonly found in target analyte lists for EPA Method 8270 (acid, base, and neutral semi-volatiles in ground water) and can be extracted using either liquid liquid extraction (LLE) or solid phase extraction (SPE).
When extracting 1,4-dioxane by LLE, recoveries are typically between 20-40%. This is largely due to the nature of the technique and, unfortunately, does not comply with the recovery requirements outlined in the method. With a 2 gram coconut charcoal cartridge, solid phase extraction can yield recoveries between 90 and 100% – in addition to the other benefits of SPE, like using less solvent! Want to learn more? Check out this previous blog post on 1,4-dioxane by SPE!