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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
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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. $\endgroup$ – Chris B. Behrens 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. $\endgroup$ – Chris B. Behrens 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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