CONCERNS ABOUT ETHYLENE OXIDE
As with many other chemicals, the use of this one brings benefits as well as risks
As far as molecules go, it is very small — only two carbon atoms, four hydrogens and one oxygen. But what an impact, positive and negative, ethylene oxide has!
The gas is an invaluable sterilizing agent for medical items such as bandages, suture and surgical implements. Its major role, though, is as a starting material for a host of consumer items.
Surfactants in detergents and shampoos, antifreeze, laxatives, beverage bottles, polyester fibres and even some glues are made from ethylene oxide. But there is a sticking point. Besides being carcinogenic, reactions involving ethylene oxide often give rise to a byproduct, 1,4-dioxane, categorized by the International Agency for Research on Cancer (IARC) as “possibly carcinogenic to humans.” That is a concern given that dioxane can be detected in personal care items, household cleaners and, more significantly, drinking water.
French chemist Charles-adolphe Wurtz first prepared ethylene oxide in 1859, but no commercial use for the compound was found until the demand for radiator antifreeze became acute during the First World War. Treatment of ethylene oxide with hot water yields ethylene glycol, to this day the most effective antifreeze for cars.
Ethylene glycol is also a key component in the production of polyethylene terephthalate resin, from which beverage bottles and polyester yarn are fabricated. It can also be polymerized to polyethylene glycol, which finds application in personal lubricants, laxatives, skin creams, toothpastes and even as a stabilizer of the MRNA in COVID vaccines.
Laundry detergents, shampoos and skin care products rely on ethoxylation, the reaction of ethylene oxide with an alcohol such as lauryl alcohol from palm kernel or coconut oil. The resulting ethoxylate is further treated with sulphuric acid, followed by neutralization with sodium hydroxide, to yield sodium laureth sulphate, a surfactant listed on numerous labels.
Surfactants are long molecules that have one end with an affinity for oil and another that is attracted to water. This allows oily residues to be removed from a surface, be it fabric, hair, skin or the kitchen floor. But here is the rub.
During ethoxylation, ethylene oxide also forms the undesired 1,4-dioxane, some of which makes it into the final product unless special methods are used to remove it. While ethoxylation is the main concern, any reaction in which ethylene glycol is used as a reagent can also produce trace amounts of this contaminant.
While no link between 1,4-dioxane and cancer has been uncovered in people, any chemical that causes cancer in animals, even if it takes a very high dose to do so, does raise concern, especially if said chemical can be routinely detected in drinking water. That is why the state of New York introduced legislation stipulating that as of 2023, laundry detergents containing more than two parts per billion of 1,4 dioxane cannot be legally sold there.
This has affected a number of products such as Arm & Hammer Clean Burst (4.3 ppb), Tide Original (3.7 ppb) and Gain Original (3.3 ppb) that exceed the limit. However, the legislation allows for a producer to apply for a oneyear waiver from compliance as long as evidence is supplied that efforts are being made to lower the levels of dioxane. Altering reaction conditions or applying a technique known as vacuum stripping can effectively reduce the presence of dioxane.
Media reported widely on the implementation of the New York law and ended up alarming many consumers who wondered if they were putting their health at risk by using the toxic detergents.
Nobody is going to be affected by wearing clothes that have been washed in detergents containing a few parts per billion of 1,4-dioxane, an insignificant amount by toxicity standards. In any case, the chemical is very water soluble so it all goes down the drain. And therein lies the problem and the reason for the legislation.
Whatever goes down the drain may come back to bite us if it is not removed by sewage treatment or municipal water filtration. While ozone treatment, as used by some facilities, can remove dioxane, standard filtration and chlorine disinfection methods are not effective. Neither do the activated carbon filters found in the popular filtration jugs remove dioxane. That's why the best way to reduce exposure to this chemical is to not introduce it into the environment in the first place.
Shampoos actually contain much more dioxane than laundry detergents, so steps need to be taken to establish limits here as well. Another approach is to reformulate and use surfactants that are not ethoxylated. Rhamnolipids, produced by a species of bacteria, or lauryl glucoside made from lauryl alcohol and glucose, are alternatives, but are more expensive and less effective than sodium laureth sulphate, which cleans extremely well while being gentle on skin and clothes.
While efforts to reduce dioxane in drinking water to below one ppb are certainly to be lauded, exposure to ethylene oxide is a bigger problem. At room temperature, ethylene oxide is a gas and can therefore be inhaled. Unlike 1,4-dioxane, it is not a “possible human carcinogen.” It is ranked in IARC'S group 1, as a “substance known to cause cancer in people.”
The question is what people, and at what sort of exposure.
For workers in chemical plants where ethylene oxide is produced by reacting ethylene with oxygen, as well as for people who live around such facilities, the concern is very real.
Within a production plant, sophisticated scrubbers can remove the chemical from the air, but inevitably some of the gas does escape into the environment. There is suspicion that the higher than expected rate of cancer in the chemical valleys of Louisiana, Texas and Sarnia, where the landscape is dotted with chemical plants, is at least partly a result of ethylene oxide exposure.
While, as one might expect, the industry denies such a link, it does seem to be confirmed by epidemiology. This has led to calls for stopping the production of ethylene oxide, but given its importance, that is totally unrealistic. However, the problem of its release into the environment can, and should be, solved by technology.
As with so many things in life, the production of chemicals comes down to a risk-benefit analysis.