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It's known that there's a lot of perchlorate contained in Mars' surface soil.

But could we take the toxic part out and make it become plantable?

If so, how might this be done in a practical way on Mars?

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    $\begingroup$ There are several cleanup technologies but it's hard to say which would be applicable for Mars. $\endgroup$
    – SF.
    Feb 20 '19 at 15:33
  • $\begingroup$ The fuss over perchlorates is really overblown. Mars is essentially covered in dust from salt flats, so your first step in soil building would probably be to wash the regolith whether the perchlorates were there or not. On top of that, perchlorates aren't all that toxic in the first place, are short-lived, and are medically easy to deal with. Heavy metals and persistent organic pollutants are likely a bigger hazard in the long run, easily accumulating in largely-closed habitats. $\endgroup$ Jul 2 at 1:23
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Perchlorate contamination is a problem on Earth. Essentially, there is a series of water treatments and bioremediation, the process of using biological systems to fix the problem.

Here is a detailed summary of one effective approach. The short answer is this:

Engineers know how to do this on Earth, and the Martian solution is likely to be an adaptation of a known solution.

Wikipedia has a good, short summary:

Several technologies can remove perchlorate, via treatments ex situ and in situ.

Ex situ treatments include ion exchange using perchlorate-selective or nitrite-specific resins, bioremediation using packed-bed or fluidized-bed bioreactors, and membrane technologies via electrodialysis and reverse osmosis. In ex situ treatment via ion exchange, contaminants are attracted and adhere to the ion exchange resin because such resins and ions of contaminants have opposite charge. As the ion of the contaminant adheres to the resin, another charged ion is expelled into the water being treated, in which then ion is exchanged for the contaminant. Ion exchange technology has advantages of being well-suitable for perchlorate treatment and high volume throughput but has a downside that it does not treat chlorinated solvents. In addition, ex situ technology of liquid phase carbon adsorption is employed, where granular activated carbon (GAC) is used to eliminate low levels of perchlorate and pretreatment may be required in arranging GAC for perchlorate elimination.

In situ treatments, such as bioremediation via perchlorate-selective microbes and permeable reactive barrier, are also being used to treat perchlorate. In situ bioremediation has advantages of minimal above-ground infrastructure and its ability to treat chlorinated solvents, perchlorate, nitrate, and RDX simultaneously. However, it has a downside that it may negatively affect secondary water quality. In situ technology of phytoremediation could also be utilized, even though perchlorate phytoremediation mechanism is not fully founded yet.

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    $\begingroup$ It's also worth considering that if ingested, the health effect of perchlorates is hypothryroidism, a condition that can be treated on one end by simply increasing your iodine intake, and on the other with medication. The real danger is inhalation, which would be a real possibility with Martian soil. $\endgroup$ Feb 21 '19 at 0:16
  • $\begingroup$ It appears that these techniques are used to bring on perchlorate concentration in the range typically found on earth - basically in the ppm range. But Mars has higher concentrations; that will require a multi-stage clean-up. The terrestrial methods mentioned are good for the final stages, but the first stage will need to work on higher levels. Note that the GAC method mentioned already requires a two-stage process on earth. $\endgroup$
    – MSalters
    Aug 2 '19 at 9:28
  • $\begingroup$ @MSalters - I'm no bioremediation engineer, but I wonder if planting and harvesting several generations of bamboo might make a good dent in the problem. $\endgroup$ Aug 2 '19 at 19:27
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    $\begingroup$ My concern is that the initial concentration might be too high, making the soil too toxic for most complex plants. Bacteria might be more suitable. But my first bet would be to just heat the soil; perchlorates aren't that stable. You get out oxygen, which is a nice thing to have. $\endgroup$
    – MSalters
    Aug 4 '19 at 9:15
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Apart from perchlorate treatment mentioned in @Chris's answer, there are some other methods which could be able to remove the perchlorate from the martian soil:

  1. Rinsing the soil with water. Perchlorate dissolves in water.
  2. Heating the soil. Perchlorate decomposes giving oxygen as byproduct.
  3. Using perchlorate eating bacteria which produce oxygen as a metabolic byproduct. That might protect the colonists from serious health problems while also giving breathable air.
  4. Replicating microbial reduction process of perchlorate using catalyst. A team of scientists found that a powerful catalyst can be created by mixing a common fertilizer called sodium molybdate, molybdenum-bipyridine complex and a common hydrogen-activating catalyst like palladium on carbon that quickly and efficiently break down perchlorate in water using hydrogen gas at room temperature with no combustion involved. It can reduce 99.99% of perchlorate even in minute concentration.

References

  1. https://skyandtelescope.org/astronomy-news/some-plants-grow-well-in-martian-soil/
  2. https://www.sciencedaily.com/releases/2021/06/210604122505.htm
  3. Davila, A., Willson, D., Coates, J., & McKay, C. (2013). Perchlorate on Mars: A chemical hazard and a resource for humans. International Journal of Astrobiology, 12(4), 321-325. doi:10.1017/S1473550413000189
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  • $\begingroup$ is it also possible to make ozone and dioxygen directly from the perchlorate? A martian ozone layer could help reflect harmful ultraviolet as its part on Earth. Ozone is also a global warming gas and thus contribute to warming Mars if terraforming takes place concurrently. $\endgroup$
    – Kav
    Aug 13 at 19:29

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