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wonkozsane042 t1_j80xceo wrote

Reply to comment by Natolx in Can the Radiation from a Sample of Depleted Uranium Sterilize? by Natolx

It's important to remember that cells are only really vulnerable to radiation damage when they are actively dividing because it's only in this stage that the DNA fragments are exposed and aren't attached to the 'scaffolding' used to securely store DNA in the nucleus. And when the DNA is stored it is readily repaired by the cell's repair mechanisms. (The DNA can still be repaired during cell division but the repair process is much easier to disrupt.) So you would have to concentrate alot of radiation energy directly into the stored 'DNA bundle', to cause enough damage to the DNA and the structure used to support it in order to overwhelm a cell's repair mechanisms. The only way to do this at this dose rate is to have the stored DNA hit by an alpha particle but the range of alpha particles from radioactive decay is so low that none would make it to your sample bacteria.

So if the bacteria are unable to move due to a lack of nutrients, and so not actively dividing, but are still at a temperature typical of their environment they would be incredibly resilient to radiation damage and you are unlikely to sterilize the sample.

Now if they were frozen it would be possible for the bundled DNA to accumulate enough damage over time to kill the bacteria once they were thawed but again not in any reasonable time frame with this does rate.

Fun fact: people who are cryogenically frozen will accumulate enough DNA damage from high energy cosmic radiation that they will effectively receive a lethal dose of radiation before being thawed if they are frozen long enough. Probably not the best financial investment over the long haul. #justsayin

edit: removed 'any reasonable time frame' from the second paragraph. / added 'at this dose rate' in the first paragraph.

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PoorSketchArtist t1_j81fssk wrote

With enough radiation though you would create a large number of ROS which can chemically stress the cells and kill them in all sorts of ways.

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Tiny_Rat t1_j82ey1r wrote

Yes, but that again requires a fairly high dose, since bacteria do have ways of dealing with ROS that can be stepped up in times of oxidative stress.

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Pertho t1_j828dke wrote

How long would someone need to be cryogenically frozen for cosmic radiation to be a significant threat? If it’s a couple lifetimes then I could still see people taking that gamble (not something I’m into myself, just enjoy learning about this). Could treatment before freezing with something like iodine or anti-radiant treatment reduce that danger?

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mfb- t1_j82iwi8 wrote

Iodine only protects the thyroid against radioactive isotopes of iodine. That's interesting after a nuclear explosion or a major power plant accident because Iodine-131 is a significant product of them, but it doesn't do anything otherwise.

> How long would someone need to be cryogenically frozen for cosmic radiation to be a significant threat?

A short-term dose of ~100 mSv is the lowest amount where we are sure it increases the cancer risk. If we assume accumulated dose during freezing acts like a short-term dose then we need ~200-300 years to get there. Damage from the freezing/thawing process is probably still your main concern here. If we look at doses so high that they can kill you short-term then we need over 1 Sv, or thousands of years. This is assuming no special shielding in any way, and it's also ignoring terrestrial radiation sources. Normally most of the radiation dose comes from that part and people get something like 2-3 mSv/year, so we would reach 100 mSv after 30-50 years or so and over 1 Sv after a few centuries.

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wonkozsane042 t1_j82vtiy wrote

mbf explains everything well. I will only add that I heard this in an online lecture (MIT graduate course on nuclear physics I believe) though the professor said he didn't actually do the calculation to determine how long that would actually take. But I would estimate it between 10000 to 100000 years factoring in all possible background radiation sources which corresponds to mbf's estimate. So maybe it's not as crazy as I was led to believe.

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Kenkron t1_j82pp3c wrote

Addendum: this is how radiation oncology works. Cancer cells are constantly dividing, healthy cells aren't, so cancer cells are killed more quickly.

That's the elevator pitch, anyways.

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