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Have any of the following metals been used in the ISS?

  • Lead: used in some batteries, and in many types of solder.
  • Mercury: used in some batteries, and in tilt switches (which I would expect have no use on the ISS).
  • Cadmium: used in some batteries, and in some photoresistors.
  • Arsenic: used in some LEDs.

If there is a policy prohibiting one or more of them, a citation would be useful.

DrSheldon
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    I can't find any direct mentions of the use of any of those materials but there is this document about "Space Station Requirements for Materials and Processes" which covers the topic. On page 28 there are mentions of Cadmium and Mercury. Lead itself is heavy so it would be avoided as much as possible anyway and apart of that it isn't really toxic in it's solid form. – GittingGud May 13 '19 at 12:33
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    Berylium is another toxic metal used in space ships, for instance the Mercury capsule. – Uwe May 13 '19 at 14:01
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    Lead solder is still considered the best solution, reliability wise, for aerospace grade electronics. Also, in some types of machinery you will need weights, and since you will need the weights to be compact on that kind of vehicle, lead (or even DU!!) would be a likely candidate.... – rackandboneman May 13 '19 at 15:28
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    this and this suggest that Cadmium is unsuitable for vacuum applications due to off-gassing, and Lead is unsuitable for high temperature vacuum applications for the same reason. Tin-Silver solder is suggested to be a better choice for vacuum. – SamYonnou May 13 '19 at 15:34
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    @GittingGud But tin whiskers might be avoided even more. – chrylis -cautiouslyoptimistic- May 13 '19 at 17:00
  • The ISS's Nickel-Hydrogen batteries don't use lead, mercury, or cadmium (at least not in bulk, and probably not at all). – hobbs May 13 '19 at 18:29
  • Also, examine what solar cell chemistry was used (seems hard to determine). Some solar cell materials, like thallium selenide, are made of severely toxic elements. – rackandboneman May 14 '19 at 16:20
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    The title of the question doesn't quite match the body, as it asks about any toxic metals, but the body specifically mentions four. Iron can be toxic, for example. – barbecue May 14 '19 at 16:23
  • @barbecue: Use the question in the title. When I wrote the question, I expected one comprehensive answer (which is typical on Space.SE). The body was what I hoped such an answer would include. Things didn't quite turn out that way, and we have several answers. I'm satisfied with the answers, so I see no need to edit the question. – DrSheldon May 14 '19 at 16:43
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    Since the ISS is in space, if we use astronomers definition, it's mostly made of metal, save for some water and possibly helium. – Antzi May 15 '19 at 00:02
  • @Antzi: Even the water is mostly metal (at least by mass). – Vikki Dec 15 '19 at 01:46

4 Answers4

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The Urine Processor in the Regenerative Environmental Control and Life Support System uses hexavalent chromium as a pretreatment solution for the urine.

Organic Marble
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    +1 As your toxin (Cr(VI) (aq)) is a heck of a lot nastier than my toxin (As as GaAs crystal) I think you should get more votes. – uhoh May 13 '19 at 23:46
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note: protests in comments have led me to add the following sentence. Arsenic is a toxic metal and arsenic is used on the ISS, but the arsenic used on the ISS as discussed below is not a toxic metal per se, instead it's a nasty, extremely toxic semiconductor.

GaAs is soluble in HCl which means if you eat it you are eating soluble arsenic. So don't eat it.

Also see this comment.

GaAs and AlGaAs are the standard substrate and heterostructure materials for infrared, red and yellow LEDs and lasers. Indicator lights and optical proximity and interrupt sensors are probably quite numerous and will all have arsenic.

You can see the red LED component in the ISS' new RGB LED lighting in @OrganicMarble's answer to Why are these astronauts green?

UHF and microwave transmitters and receiver front ends for everything from communications and data to radar ranging for spacecraft docking to GPS are likely to have some high-speed GaAs bipolar transistor devices in them.

Arsenic has been a common dopant for a half-century in silicon based electronics and even the substrate wafers themselves can sometimes be moderately doped.

uhoh
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  • Yup, I expected LEDs to be ubiquitous inside the ISS, and thus arsenic. Fortunately, it is so deeply encapsulated (in a crystal, in an epoxy case, inside an instrument) that exposure is nearly impossible. – DrSheldon May 13 '19 at 13:38
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    @Dr Sheldon: Not only is it embedded, the amounts used as dopants are miniscule and the actual LED is on the order of a micrometer thick. Remember that the dose makes the poison: there just isn't enough in the LEDs to be harmful. – jamesqf May 13 '19 at 16:33
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    @jamesqf in the case of GaAs (red LEDs, bipolar RF chips) it's the substrate itself that is gallium arsenide, the arsenic is not just a dopant, it's half the wafer! While GaN (blue and white light LEDs) tends to be a thin epitaxial layer on sapphire, the GaAs parts are made from the wafers themselves. – uhoh May 13 '19 at 16:35
  • Isn't GaAs used for the solar panels as well? – CBredlow May 13 '19 at 17:38
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    @CBredlow While many satellites use higher efficiency dual and triple junction PV cells that include III-V materials, the ISS' panels are just silicon. See answers to Why does the ISS not use the most efficient solar panels available? as well as How are the silicon PV cells constructed in the ISS's solar panels? Are they as flexible as they appear here? I don't know if there is arsenic doping in them. – uhoh May 13 '19 at 17:50
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    The LED wafers used in typical indicator LEDs are pretty small, too -- I don't have an exact size, but it's on the same scale as a grain of salt. Easily under 1% of the volume of the LED. –  May 14 '19 at 01:07
  • @duskwuff indeed, wafer thinning and dicing these days is amazing! – uhoh May 14 '19 at 01:29
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    @uhoh: Gallium arsenide is not arsenic, any more than carbon dioxide is oxygen. To get into the body, you'd somehow have to decompose it into gallium & arsenic. – jamesqf May 14 '19 at 05:18
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    @jamesqf The question asks only "Were any toxic metals used in the International Space Station?" and I've answered the question as asked. There's absolutely nothing in the question about getting anything into ones body; you're bringing that up yourself for some reason and I don't know why. It's a non sequitur. – uhoh May 14 '19 at 07:39
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    There are certainly also InGaAs detectors somewhere in/on the ISS for NIR spectroscopy, etc. – J... May 14 '19 at 12:19
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    Jamesqf's point is that GaAs has low toxicity. The very notion of toxicity is defined by biological response. Just because one of the atoms in a compound is toxic elementally doesn't mean it's toxic in a tightly bound compound, and it can also be even more toxic in other compounds (see organoarsenic compounds). Also, GaAs isn't a metal. – user71659 May 14 '19 at 16:09
  • @user71659 I understand the concept, I've had GaAs wafer pieces in my hand and I even paid someone to put mercury in my mouth. The question is pretty short and doesn't go into details about the situation. It doesn't specifically ask if these things are in a dangerous form on the ISS. I'll add a sentence at the top of my answer... – uhoh May 14 '19 at 16:24
  • @uhoh: Gallium arsenide is not arsenic. it's a compound, and as such it has entirely different properties than its constituent atoms. You'd have to decompose it into Ga and As to get toxicity. Likewise, I expect that there are significant amounts of sodium chloride on the ISS (including within the crew's bodies :-)). Chlorine is toxic; sodium might be, but it's hard to tell because it would burst into flame on contact with saliva. – jamesqf May 15 '19 at 17:12
  • @jamesqf that's right, so I won't be eating any bare III-V devices any time soon, lest they decompose in my HCl. – uhoh Jul 28 '21 at 03:22
  • @jamesqf Heavy metal toxicity is the function of water and/or lipid solubility of the specific metal's compound and its metabolites. Depending on the dose, gallium arsenide exposure produces the same systemic toxicity effects with the same range of symptoms as exposure to elemental arsenic, As₂O₃, or any other inorganic form of arsenic that is able to react with or dissolve in the bodily fluids; once the compound reacts to get solubilized, the arsenic-containing species are absorbed and it does not matter whether they initially came from elemental As or from a compound. {continues} – No Nonsense May 13 '22 at 21:39
  • @jamesqf Refuting that fact by claiming that "Gallium arsenide is not arsenic. it's a compound [...] you'd have to decompose it into Ga and As to get toxicity" ignores crucial biochemical context: what matters in the context of heavy metal toxicity is only whether or not a given compound is biologically available source of a toxic element. In case of more chemically inert metals, it is actually much easier to cause that specific metal's toxicity syndrome with its compounds, rather than with the elemental form. {continues} – No Nonsense May 13 '22 at 21:45
  • @jamesqf Liquid mercury is much less toxic upon oral ingestion that water-soluble salts of this metal, for example. And your example of "significant amounts of sodium chloride on the ISS [...] Chlorine is toxic; sodium might be, but it's hard to tell because it would burst into flame on contact with saliva." completely misses the point. Sodium chloride contains its constituent elements in the form of ions, Na⁺ and Cl⁻, none of which are toxic (they are essential electrolytes, after all). Meanwhile, GaAs contains {continues} – No Nonsense May 13 '22 at 21:52
  • @jamesqf arsenic in the form of arsenide (As³⁻), which is extremely toxic, much like other inorganic forms of arsenic. Answer from uhoh does not contain any incorrect claims and your arguments are both invalid and unconstructive. Cheers. – No Nonsense May 13 '22 at 21:55
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The bearings on the CMG (Control Moment Gyro) rotors use beryllium, which is pretty toxic when you machine it.

Tristan
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    Also, heatsinks and ceramic parts in high performance radio and radar gear tend to use beryllium oxide, which is even more toxic if you disintegrate this (brittle!!) material in any way.... Also, bearings are somewhat self machining.... – rackandboneman May 13 '19 at 15:24
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    @rackandboneman Not even high performance: your microwave oven magnetron has BeO2 ceramic insulators. You recognize it by pink coloring. It's safe unless you're grinding it. – user71659 May 13 '19 at 22:10
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    A compact 800W transmitter is high performance RF stuff, even if you use it to heat a non-aerospace grade soup. – rackandboneman May 14 '19 at 08:19
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The heating system has ammonia in one of its loops, which is very irritating to human eyes, nose, throat, and lungs. On Earth, you can just leave spilled ammonia for a few hours, and it will waft away into the atmosphere until it's at a low enough concentration to be tolerable. In a space habitat, it would be terrible. You might be able to get everyone into space suits, evacuate the atmosphere, and refill the atmosphere. However, the ammonia would seep into fabric and plastic and be difficult to completely exhaust.

Ammonia is a good refrigerant, and it's still usable below the freezing temperature of water, which is why they tolerate it on the ISS. The 2019 news about neopentyl glycol being a viable solid refrigerant is great... if it's usable as a refrigerant at both cold and human-range temperatures, then spacecraft cooling can be made safer and more reliable.

Christopher Hostage
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