Our story starts with 鈥渟urfactants,鈥� a term derived from 鈥渟urface active agents.鈥� These are molecules with one end being 鈥渉ydrophilic鈥�, meaning it is attracted to water, while the other 鈥渉ydrophobic鈥� end is attracted to oily substances or to air. If you like your shampoo to form a luxurious lather, disdain stains on your clothes and dishes and don鈥檛 want your face cream to separate into layers, then you want surfactants in your life. But surfactants aren鈥檛 grown in fields or harvested from trees, not directly anyway. They have to be chemically synthesized. And therein lies the problem.
There are a number of surfactants in common use. Some have better foaming properties, some are better cleaning agents, and some are better at not allowing the oily and aqueous layers in cosmetics to separate. Before going any further, it is important to make clear that surfactants in a product do not present a health risk to the user. The issue is about 1,4 dioxane, a manufacturing byproduct, that may eventually end up in the water supply. This contaminant can form during the synthesis of 鈥渁lkyl ether sulfates,鈥� valued for their foaming properties, or the 鈥渁lcohol ethoxylates鈥� prized for their detergency.
Let鈥檚 use 鈥渟odium laureth sulfate (SLES),鈥� a typical 鈥渁lkyl ether sulfate,鈥� to shed light on the problem. The manufacture of this compound begins with palm kernel oil or coconut oil both of which are rich in lauric acid. Treating this with hydrogen produces lauryl alcohol that is then reacted with ethylene oxide to yield 鈥渓auryl alcohol ethoxylate.鈥� Finally, treatment with sulfur trioxide and sodium hydroxide produces the final product, SLES.
The problem tracks back to the step that uses ethylene oxide. In a side reaction, two molecules of ethylene oxide can join together to form the infamous 1,4 dioxane. The concern is that if this contaminant isn鈥檛 removed during processing, it ends up going down the drain and may eventually make it into water systems from which our drinking water is sourced. Neither sewage treatment nor water purification systems are designed to remove traces of chemicals such as 1,4-dioxane meaning that they can end up in our drinking water and therefore in us. Which brings up the question, 鈥渟o what?鈥�
Here's the scoop on the 鈥渟o what.鈥� The International Agency for Research on Cancer (IARC) has classified 1,4-dioxane as 鈥減ossibly carcinogenic to humans鈥� and the U.S. National Toxicology Program views it as 鈥渞easonably anticipated to be a human carcinogen.鈥� Neither of these evaluations is based on human epidemiological evidence but rather on finding liver tumours in rodents that had consumed drinking water laced with the chemical over a long-term. However, these rodents were drinking water that had a concentration of 5000 parts per million (ppm) of 1,4-dioxane, a dose to which no human could ever be exposed. But it is common practice to use such large doses in rodents over their relatively short life to estimate the effects of low doses to which humans could be exposed over their much longer lifetime. That is how Health Canada arrived at its maximum allowed concentration of 0.05 ppm in drinking water. This is some 100,000 times less than the concentration of 1,4-dioxane in the rodents鈥� drinking water. Furthermore, what is actually found in drinking water is a fraction of that maximum.
While the cancer risk posed by 1,4-dioxane in tap water is negligible, it is not the only trace chemical with a hint of danger to which we are exposed in our water and food. There are numerous contaminants that can be traced to the production of medications, pesticides, apparel, plastics and personal care products that introduce their own toxicity issues. While the individual toxicities may be very small, there could well be a cumulative effect. That is why it is important to reduce any possible contaminant as much as possible. As far as 1,4-dioxane is concerned, technologies such as steam distillation and vacuum stripping are available to reduce its concentration in shampoos, cosmetics and detergents to 1 ppm which virtually eliminates its possible presence in drinking water.
Another way to tackle the problem is to stay away from surfactants that require the use of ethylene oxide in their production. Sodium lauryl sulfate (SLS) is a case in point. There is no chance of contamination with 1,4-dioxane but it is harsher on the skin than SLES. It is such an effective surfactant that it can strip away the skin鈥檚 natural oils and cause irritation. There are also nonsensical internet rumors about SLS causing cancer. Sodium coco-sulfate and alkyl polyglucosides are other surfactants you may find on labels. These do not require ethylene oxide in their production and are gentler on the skin than SLS.
There is another connection with 1,4-dioxane that merits a mention. Polyethylene glycol (PEG) is a widely used synthetic compound with numerous applications. For example, because of its ability to hold on to moisture, it is the active ingredient in laxatives such as MiraLAX and Lax-A-Day. Since its production involves the use of ethylene oxide, it can have trace residues of 1,4-dioxane. Pharmaceutical manufacture is strictly regulated, and these laxatives cannot contain more than 10 ppm of 1,4-dioxane which is thought to be inconsequential. Laxatives such as Metamucil are not made with polyethylene glycol and therefore cannot harbour 1,4-dioxane as a contaminant. Polyethylene glycol derivatives such as PEG-stearate are effective emulsifiers and are found in a variety of face creams, lotions and sunscreens. These may introduce trace but inconsequential amounts of 1,4-dioxane.
One final point. I few years ago I got a call from a mom who was outraged when she discovered that her child鈥檚 shampoo was contaminated with dioxin, the notorious highly carcinogenic compound that had been detected in Agent Orange, the defoliant that was sprayed from airplanes during the Vietnam War. Dioxin, a truly dangerous substance, was a contaminant in Agent Orange but it is a totally different substance from dioxane. The worried mom had read some article that described the 1,4-dioxane issue and she had also read about dioxin in Agent Orange. She had confused dioxin with dioxane and panic ensued. When it comes to chemicals, details are important! If there really was dioxin in my shampoo, I would be concerned. 1,4-Dioxane, not so much.
