D5 is a cyclomethicone fluid commonly used in cosmetics such as deodorants, sunblocks, hair sprays and skin care products. It is becoming more common in hair conditioners, as it makes the hair easier to brush without breakage.
D4 used in polishes has recently been flagged up in lab studies that claim the compound is toxic to small rainbow trout after trickling down through household drains and into the environment.
The UK is planning to submit restriction proposals on the substances in January 2015, based on concerns about their "persistent, bioaccumulative and toxic (PBT) and very bioaccumulative (vPvB) properties".
The restrictions would stop the substances from being placed on the market, or being used, in concentrations equal to, or higher than, 0.1% by weight in personal care products that are washed off in normal use conditions.
Studies into potential toxicity in D4 and D5
These substances are not currently regulated anywhere in the world and over the past decade, D5 has largely replaced D4 in cosmetics.
Back in 2006, the science panel of the European Commission reviewed data on octamethylcyclotetrasiloxane and concluded that it was unable to assess the risk to consumers used in cosmetic products.
“Despite the size of the paperwork submitted by industry for evaluation, it is unfortunate that the dossier lacked meaningful information/data on actual consumer exposure to D4,” the panel said.
However, the EPA announced last year that it would evaluate whether D4 should be regulated under the Toxic Substances and Control Act. However, the agency is less concerned about outdoor air concentrations than it is about the risks to water-dwelling creatures, says an EPA spokesperson.
Both substances are “safe for human health and the environment when used as intended,” says Karluss Thomas, senior director of the American Chemistry Council’s Silicones Environmental, Health and Safety Center.
In the US, California health officials have expressed concern about this growth in use of D5, saying in 2007 that “it has potential public health impacts”.