Potentially harmful chemicals have been found in dust collected from the International Space Station, researchers announced on Wednesday.
After what was the first study of its kind, researchers said their findings could help design better spacecraft.
Scientists analysed a sample of dust from air filters inside the ISS and compared them to organic contaminants found in houses on Earth.
Some of the chemicals they found are classed as pollutants and even carcinogenic, researchers from the University of Birmingham, England, and Nasa Glenn Research Centre, in the US, said.
“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,” said Professor Stuart Harrad from the University of Birmingham.
“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.”
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).
Some of the chemicals are classed as persistent organic pollutants (POPs) under the UNEP Stockholm Convention, and some PAH are classified as human carcinogens.
Researchers said the effects on human health have led to some of the chemicals being banned or limited in use on Earth.
PAHs are present in hydrocarbon fuels and emitted from combustion processes.
BFRs and OPEs can be used to meet fire safety regulations in consumer and commercial applications like electrical and electronic equipment, building insulation, furniture fabrics and foams.
PCBs were used in building and window sealant, and in electrical equipment, while PFAS have been used in applications like stain proofing agents for fabrics and clothing.
According to the researchers, the use of off-the-shelf items brought on board by astronauts for personal use, such as cameras, MP3 players, tablet computers, medical devices, and clothing, are potential sources of many of the chemicals detected.
The air inside the ISS is constantly recirculated with eight to 10 changes per hour, the study published in Environmental Science and Technology Letters found.
While carbon dioxide and gaseous trace contaminant removal occurs, the degree to which this removes chemicals like BFRs is unknown.
High levels of radiation can accelerate the ageing of materials, including the breakdown of plastic goods into micro and nanoplastics that become airborne in the microgravity environment.
The study suggests this may cause concentrations and relative abundance of chemical contaminants in the ISS dust to differ notably from those in dust from indoor micro-environments on Earth.
Scientists measured concentrations of a range of target chemicals in dust collected from the ISS.
In a microgravity environment like that on the space station, particles float around according to ventilation system flow patterns, eventually depositing on surfaces and air intakes.
Screens covering the filters accumulate this debris, requiring weekly vacuuming to maintain efficient filtration.
The material in ISS vacuum bags comprises previously airborne particles, clothing lint, hair and other debris generally identified as spacecraft cabin dust.
Some vacuum bags were returned to Earth for studies of this unique dust, with a small sample shipped to the University of Birmingham for analysis.