The International Space Station (ISS) has been continuously occupied for more than 20 years. But what kind of compounds end up in the air filter?
A new paper – published today in Environmental Science and Technology Letters – analysed space dust from the air filters aboard the ISS, finding a plethora of chemical contaminants in concentrations higher than many American homes.
Full vacuum bags from the ISS HEPA filters were returned to Earth for the study, and after filtering it through a sieve with micrometre sized holes, the researchers ended up with about 200 mg of concentrated sample.
Contaminants found in the ‘space dust’ included polybrominated diphenyl ethers (PBDEs), hexabromocyclododecane (HBCDD), ‘novel’ brominated flame retardants (BFRs), organophosphate esters (OPEs), polycyclic aromatic hydrocarbons (PAH), perfluoroalkyl substances (PFAS), and polychlorinated biphenyls (PCBs).
“Also of note, the concentration of perfluorooctanoic acid (PFOA) in ISS dust (3,300 ng/g) exceeds the maximum reported (1,960 ng/g) in a 2008 survey of dust from US child daycare centers and homes,” the researchers write in their paper.
“This maybe reflects the widespread use of waterproofing treatments in the ISS to prevent microbial growth.”
Some of these compounds – like PFAS – are controversial and have been linked health problems in non-human models. PFAS in particular is known as a ‘forever chemical’.
PCBs, some PFAS, HBCDD and some PBDEs are classed as persistent organic pollutants under the UNEP Stockholm Convention. On top of that, some PAH are classed as carcinogens.
This might sound scary, although if you’re a would-be astronaut don’t be too worried just yet.
“While concentrations of organic contaminants discovered in dust from the ISS often exceeded median values found in homes and other indoor environments across the US and western Europe, levels of these compounds were generally within the range found on Earth,” says Professor Stuart Harrad from the University of Birmingham.
“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.”
The reason that these chemicals are there is the same reason that we see them on Earth – chemicals are just part of our lives.
BFRs and OPEs are normally found in electrical and electronic equipment, building insulation, furniture fabrics and foams, and are used in many countries to meet fire safety regulations.
PAH are part of hydrocarbon fuels and released as waste, PCBs were used in building and window sealants and in electrical equipment as dielectric fluids, while PFAS are found in fabrics and clothing.
The research is not only helpful for the ISS, but reminds us that whatever we put into our environment is likely to end up inside us, and being careful about the chemicals we choose is important.