Think International Space Station dust is obviously free of bad chemicals? Wrong

No one's in danger but we may need to rethink some cabin materials

The International Space Station has perhaps a bit of a housekeeping issue on its hands. Analysis of dust samples from its air filters suggest astronauts are likely exposed to higher levels of dangerous chemicals than those of us stuck on Earth, on average.

In a report published this week in the Environmental Science & Technology Letters journal, folks at the UK's University of Birmingham and NASA's Glenn Research Center said organic contaminant levels in ISS dust exceeded the median values reported in many US and western European homes. 

Below is a table, taken from the above peer-reviewed paper, listing the concentrations of chemicals found in dust collected on the ISS, compared with what some of us experience on Earth. ("ns" means not significant.) The space dust is mostly above the median though typically within the household range.

Compound class	Chemical	Concentration in ISS dust (ng/g)	Median (range) concentration in US house dust (ng/g)
PBDEs	BDE-28	220	4.6 (<1–2300)
	BDE-47	8400	420 (ns-130 000)
	BDE-100	2700	89 (ns-69 000)
	BDE-99	27 000	580 (ns-140 000)
	BDE-154	1900	42 (ns-36 000)
	BDE-153	3600	56 (ns-44 000)
	BDE-183	230	15 (<2–1100)
	BDE-209	18 000	910 (ns-990 000)
NBFRs	HBBz	530	4.7 (<1–1100)
	EH-TBB	790	1200 (<5–130 000)
HBCDDs	α-HBCDD	2300	240 (ns-17 000)
	β-HBCDD	1000	38 (ns-14 000)
	γ-HBCDD	95 000	89 (ns-300 000)
OPEs	EHDPP	59	1100 (ns-42 000)
	TCEP	13	530 (ns-32 000)
	TDCIPP	15	3500 (ns-170 000)
	TCIPP	15	5400 (ns-150 000)
	TPhP	15 700	8100 (ns-110 000)
	TnBP	160	200 (<30–1200)
PCBs	PCB-52	19	6.2 (1.7–28)
	PCB-101	190	8.7 (1.9–29)
	ΣPCBs	210	200 (47–620)
PFAS	PFOS	23	200 (<8.9–12 000)
	PFOA	2,600	140 (<10–1960)
	FOSA	3.7
	PFHxS	3.7	46 (<13–36 000)
	PFBS	3.5	0.9 (<LOQ-2.6)
	EtFOSE	1.0	<LOQ (<LOQ-94)
	MeFOSE	52	1.0 (<LOQ-9.9)
	PFNA	50	3.9 (1.1–63)
PAH	acenaphthene	930	5.5 (1.3–25)
	phenanthrene	830	95 (25–390)
	anthracene	48	9.6 (2.0–73)
	fluoroanthene	150	76 (12–360)
	pyrene	1600	80 (20–300)

Examples of such compounds include polybrominated diphenyl ethers, or PBDEs; novel brominated flame retardant (NBFR); and hexabromocyclododecane (HBCDD), all flame retardants. Polycyclic aromatic hydrocarbons (PAHs), released by combustion of hydrocarbon fuels, were also present in elevated levels. 

Polychlorinated Biphenyls, or PCBs, a widely used range of chemicals banned from production in America in 1979, were also found in ISS dust, in one case well in excess of the range found in US homes. Per- and polyfluoroalkyl substances, more commonly known as PFAS, were also found in elevated levels, with the presence of stain-resisting chemical PFOA particularly high.

Mostly harmless?

Just because the levels of harmful chemicals in ISS dust are elevated, it doesn't mean they immediately pose a threat to astronauts, University of Birmingham Professor of Environmental Chemistry Stuart Harrad, one of the paper's coauthors, told The Register.

"ISS astronauts are exposed to potential health risks from these compounds at a greater level than most Americans but their exposure is within the range experienced by the American public," Harrad noted.

"To put it bluntly, it is possible that you or I could be exposed at higher levels than the astronauts; though more likely that they are more exposed than us."

Prof Harrad said the compounds identified in the study are generally known to be harmful after cumulative exposure, and thus aren't an immediate threat to astronaut health. What's more, it might not even be the ISS' own equipment that's the issue. 

"We think much of what we see on the ISS is due to off-the-shelf items brought on board by the astronauts that contain organic flame retardants used on Earth in electrical items," Harrad said.

Likewise, it's possible not all of the dust collected in the samples was airborne and could have been collected thanks to the cleaning habits of ISS residents. 

"Occasionally the vacuum cleaner is used to clean up materials after an experiment is performed, resulting in higher concentrations of some materials not indicative of typical airborne material concentrations," the team noted in its study.

Occasionally the vacuum cleaner is used to clean up materials after an experiment is performed

Additionally, regular vacuuming of surfaces and air intakes likely pulls loose bits of protective coatings, like flame retardants, off of wall panels and insulation, the authors – Mohamed Abou-Elwafa Abdallah, Daniel Drage, and Marit Meyer as well as Harrad – observed.

Still, the presence of higher-than-average levels of harmful compounds on the ISS should have design implications for future space missions, the researchers concluded. 

"On future missions to, for example, Mars of ~9 month duration one way, it is clearly a good idea to minimise concentrations of the sorts of contaminants we measured to minimise any long-term effects on astronaut health," Prof Harrad said.

He told us that he believed NASA is already using less harmful inorganic flame retardants in fabric on the ISS, and said he expects NASA would already be actively looking into safer alternatives for PFAS compounds as they face more bans over health and environmental concerns. ®