International Space Station may be more polluted than most American homes

Concentrations of toxic contaminants found in dust on the International Space Station (ISS) surpass those found in floor dust in many U.S. households, a new study has found.

Levels of organic pollutants in dust samples from ISS air filters were higher than the median values found in U.S. and Western European homes, according to the study, published on Tuesday in Environmental Science and Technology Letters.

“Our findings have implications for future space stations and habitats, where it may be possible to exclude many contaminant sources by careful material choices in the early stages of design and construction,” co-author Stuart Harrad, a professor of environmental chemistry at the University of Birmingham, said in a statement.

Contaminants identified in this so-called “space dust” included polybrominated diphenyl ethers (PBDEs), hexabromocyclododecane (HBCDD), “novel” brominated flame retardants (BFRs), organophosphate esters (OPEs), polycyclic aromatic hydrocarbons (PAH), per- and polyfluoroalkyl substances (PFAS), and polychlorinated biphenyls (PCBs).

Certain commercially-formulated PBDEs are classified as persistent organic pollutants under the United Nations Environment Program’s Stockholm convention, as are PCBs, some types of PFAS and HBCDD, the authors noted.

Meanwhile, some PAH have been classified as human carcinogens, and some OPEs are under consideration for restriction by the European Chemicals Agency. 

BFRs and OPEs are used in many countries to meet fire safety regulations in applications like electrical equipment, building insulation, furniture fabrics and foams, the researchers explained.

PAH are emitted in combustion processes associated with hydrocarbon fuels, while PCBs were used in building and window sealants and in electrical equipment.

PFAS, also known as “forever chemicals,” are key ingredients in certain kinds of firefighting foams, as well as in many consumer products, such as non-stick pans, waterproof apparel and cosmetics.

The presence of PBDE in the ISS dust samples could be coming from inorganic fire retardants, which are used to prevent fabrics and webbing from igniting, the authors hypothesized.

The ISS houses “a unique indoor environment inhabited by humans for over 20 years since its launch in November 1998,” the scientists noted. The vulnerability of spacecraft to fire means that “very careful attention is paid to the flammability of ISS contents,” they explained.

The air inside the ISS is constantly recirculated, with eight to 10 changes per hour, according to the study. While the system does eliminate carbon dioxide and gaseous trace contaminants, it is unknown to what degree it can remove chemicals like flame retardants. 

In addition to fire retardants, the researchers also identified the presence of “off-the-shelf” items on board — such as cameras, MP3 players, tablets, medical devices and clothing — as possible sources of many of the chemicals they detected.

Although levels of these contaminants exceeded those of many U.S. and Western European households, Harrad stressed that the concentrations of these chemicals “were generally within the range found on Earth.”

Nonetheless, Harrad and his colleagues expressed hope that their findings could be an asset as policymakers plan for a future that increasingly reaches beyond the bounds of Earth.

“The results do have implications for future space stations and habitats, where it may be possible to exclude many contaminant sources by careful material choices in the early stages of design and construction,” they concluded.