The accumulation potential and toxicity of cyclic siloxanes are debated by scientists and industry representatives.
Both D4 and D5 are “safe for human health and the environment when used as intended,” Karluss Thomas, senior director of the American Chemistry Council’s Silicones Environmental, Health and Safety Center, said in an emailed response.
He said higher levels of the compounds in places such as Chicago are not cause for concern because there is no evidence they harm humans.
But a science panel of the European Commission that reviewed existing data about D4 concluded in 2006 that it was “unable to assess the risk to consumers when D4 is used in cosmetic products.”
“Despite the size of the dossier submitted by industry for evaluation, it is unfortunate that the dossier lacked meaningful information/data on actual consumer exposure to D4,” the panel said.
Over the past decade, D5 has largely replaced D4 in cosmetics, according to cyclic siloxane studies.
California health officials have expressed concern about this growth in use of D5, saying in 2007 that “it has potential public health impacts” and “has been measured in several aquatic species at parts per million concentrations, and appears to have a long half-life in humans. Thus, D5 persistence in the environment and in animal and human tissues is a concern.”
How the chemicals build up in aquatic creatures is not well understood.
However, other research shows the compounds were accumulating in the food chains of Norway’s Lake Mjosa and England’s Humber Estuary, according to work by Michael McLachlan and Stockholm University colleagues.
McLachlan said the compounds have an odd structure that makes it difficult to understand them, but he said that most scientists say they are accumulating. “Standard chemicals usually mostly end up in sediment,” McLachlan said. “However, with cyclic siloxanes, a much smaller portion ends up in sediment and a much larger portion ends up in fish.”
With elevated levels in Chicago’s air, it’s possible that wildlife in the world’s largest freshwater source – the Great Lakes – are contaminated with them, but no one has looked yet, Hornbuckle said. Labs across the Great Lakes region are investigating ways to measure the chemicals, according to a 2010 study on emerging contaminants in the Great Lakes from Environment Canada.
Cyclic siloxanes are world travelers. It takes about two weeks for D4 and D5 to degrade in the atmosphere. “Air can circle the entire globe in a week,” McLachlan said.
In 2011, Canadian researchers sampled air at 20 sites worldwide – including five in the Arctic – and found the compounds in all places. In winter, when there is less sunlight to break down the chemicals, the Arctic sees a spike, McLachlan said.
Researchers also have found that wastewater treatment plants and sewage sludge are highly contaminated with the chemicals.
“They [cyclic siloxanes] are much different compared to other environmental chemicals,” McLachlan said. “We’re really just starting to understand how they behave.”
This article originally ran at Environmental Health News, a news source published by Environmental Health Sciences, a nonprofit media company.