I'm sceptical of the claim that they couldn't eliminate the majority of them from stuff that's shipped up to the ISS. Even if it meant making special space certified hair conditioner.
There's a nice paper on this, ICES-2018-123 "Dimethylsilanediol (DMSD) Source Assessment and Mitigation on ISS: Estimated Contributions from Personal Hygiene
Products Containing Volatile Methyl Siloxanes (VMS)". The upshot is more than half of the siloxane burden on ISS comes from God knows where (packaging, plastics, machinery, you name it).
> The main sources of VMS were determined to be antiperspirants ... skin lotions ... wipes ... and hair conditioner. Several siloxanes-free options are available for [these products]. These products are now being assessed for crew member use in future increments.
From the blog:
> At present the agency is testing a new filtration system to put in front of the heat exchangers, to try to protect them, and continuing to try to cut down on siloxanes at the source level. There are probably people at NASA now whose entire career has been built on siloxane control.
Why wasn't the result to simply ban siloxane-containing cosmetics and wipes? The cosmetics are up to the individual astronaut, which is a little crazy, but the wipes are provided by NASA, and they're still using siloxane-bearing wipes, which shortens the life of their water systems and costs crazy amounts of money.
You can't just replace stuff in a sealed environment - if the new stuff is better in one way it might be worse than others. Gotta do the qualification work - remember they're drinking piss up there.
> Why wasn't the result to simply ban siloxane-containing cosmetics and wipes?
I would assume there is an approval process in place and alternatives have to go through this process before they can be sent up. It might take months or years for approval.
It's really, really complicated. Even "organic" or "all natural" products often contain synthetic contaminants as a result of manufacturing, packaging, or shipping processes. Unless NASA were to set up separate factories and supply chains for manufacturing all known sources of siloxane contamination (either on their own or in partnership with manufacturers), it would be very difficult to actually get a siloxane-free product with any kind of certainty or consistency.
An example with a different contaminant: We can't seem to keep carcinogenic plasticizers out of our RXBars and our baby formula[1]. Those products are already way more regulated than something like wet wipes, and the companies that make them have a strong interest in keeping them free of contamination.
https://ttu-ir.tdl.org/items/ff1a240e-1fb1-4b04-acb2-42e9c45...