International space station polluted with harmful chemicals

Chemicals found in the air filters

The scientists examined vacuum bags from the ISS HEPA filters returned to Earth for this investigation. Moreover, the "space dust" samples were compared with the organic pollutants in American homes.

A diverse variety of chemical pollutants were detected in the space dust samples, which mainly 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).

The applications for BFRs and OPEs include electrical and electronic equipment, building insulation, furniture textiles, and foams. These compounds are also used to ensure fire safety regulations.

PAHs are often found in hydrocarbon fuels and are released during combustion processes.

PCBs are commonly used in building and window sealants, as well as electrical equipment. While PFAS, also known as forever chemicals, are found in fabrics and clothing. 

However, the authors highlight that the chemicals' impacts on human health have resulted in some being banned or restricted for usage.

According to the UNEP Stockholm Convention, some substances are designated persistent organic pollutants (POPs), while some PAH are listed as human carcinogens.

But how did these chemicals end up on board the space station?

Chemicals are ubiquitous in our daily lives and widely used in various applications. 

As per the official release, the “off-the-shelf items” brought on board by astronauts for personal use, like cameras, MP3 players, tablet computers, medical gadgets, and clothes, could be probable sources of several of the chemicals found in the study.

While some chemical contaminants could originate from the existing space station's infrastructure.

Meanwhile, onboard the ISS, some systems continually recirculate inside the air at a pace of eight to ten changes each hour.

This methodology allows for eliminating carbon dioxide and gaseous trace pollutants, but the extent to which chemicals like BFRs are removed is unknown.

The researchers hope their results will help engineers design and build better long-term human space stations.

“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 Harrad. 

The findings were published in the journal Environmental Science and Technology Letters.

Study abstract:

Polybrominated diphenyl ethers (PBDEs), hexabromocyclododecane (HBCDD), “novel” brominated flame retardants (NBFRs), organophosphate esters (OPEs), polycyclic aromatic hydrocarbons (PAH), perfluoroalkyl substances (PFAS), and polychlorinated biphenyls (PCBs) were measured in a composite sample of dust from the International Space Station (ISS). Notwithstanding the unique environment from which the dust originated, while concentrations of all target compound classes frequently exceeded the median values in terrestrial indoor microenvironments in the US and western Europe, ISS dust concentrations were generally within the terrestrial range. The relative abundance of the three HBCDD diastereomers is dominated by γ-HBCDD (96.6% ΣHBCDD). This matches very closely with the commercial mixture added to materials and contrasts with the diastereomer distribution observed in most terrestrial indoor dust samples (in which γ-HBCDD is typically ∼60–70% ΣHBCDD). This suggests conditions inside the ISS do not favor the previously reported photolytically mediated formation in dust of α-HBCDD. Also of note, the concentration of perfluorooctanoic acid (PFOA) in ISS dust (3300 ng/g) exceeds the maximum reported (1960 ng/g) in a 2008 survey of dust from US child daycare centers and homes. This may reflect the widespread use of waterproofing treatments in the ISS to prevent microbial growth. Our findings can inform future material choices for manned spacecraft such as the ISS.