Is it true that bleach does not destroy DNA?

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Thread: Is it true that bleach does not destroy DNA?

  1. #1

    Is it true that bleach does not destroy DNA?

    I read that it did, so I wrote my story so that the villains use bleach to destroy their DNA from the crime scenes. After a couple of more readers read it though, they said bleach does not actually destroy DNA, and that it's actually a myth though. Is that true? If so, is there any other thing you could wipe a crime scene down with to get rid of DNA, or no?

  2. #2
    It is true - bleaches aren't generally effective at destroying DNA evidence, because they just don't work that way. A bleaching agent usually works by oxidizing, or less often reducing, certain types of molecules it is meant to act against. Most common types of bleaches are based either on chlorine or oxygen (usually in peroxide form). Bleaching agents typically denature rather than dissolve proteins, making them ineffective at destroying substances like DNA (because if they were effective destroyers of organic matter, they wouldn't be much good as bleaches). What a would-be criminal needs is a powerful solvent rather than a bleaching agent.

    With modern forensic technologies, it is literally possible to obtain identifiable DNA from the shit-stain left on a window pane by a fly that has fed on a missing person's corpse (yes, an actual murder case was solved this way). So it's not so much about the possibility of destroying DNA evidence with chemicals as the impossibility of destroying ALL of it. It would therefore be more practical for a criminal to leave as little DNA evidence that could be traced back to him as possible rather than go out of his way to expend large amounts of bleach trying (in vain) to whitewash the crime scene, the bleach itself being a possible evidence whose purchase could be traced to the offender.

  3. #3
    Oh okay, thanks. What would be a more effective way of destroying the DNA then, if any?

  4. #4
    A lot of OR-grade cleaners may. You'll have to do a search, but look for surgical cleaning agents. There's alcohol, of course. Quaternary compound, good ol' hydrogen peroxide for cleaning up puddles of blood... I don't know which, if any, actually destroy DNA, but I think this might bear exploring a little... There are liquid sterilization agents that are used for endoscopes and other rubber/delicate items that can't go into the steam autoclave. Good luck!
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  5. #5
    WF Veteran Bloggsworth's Avatar
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    Quote Originally Posted by CyberWar View Post
    It is true - bleaches aren't generally effective at destroying DNA evidence, because they just don't work that way. A bleaching agent usually works by oxidizing, or less often reducing, certain types of molecules it is meant to act against. Most common types of bleaches are based either on chlorine or oxygen (usually in peroxide form). Bleaching agents typically denature rather than dissolve proteins, making them ineffective at destroying substances like DNA (because if they were effective destroyers of organic matter, they wouldn't be much good as bleaches). What a would-be criminal needs is a powerful solvent rather than a bleaching agent.

    With modern forensic technologies, it is literally possible to obtain identifiable DNA from the shit-stain left on a window pane by a fly that has fed on a missing person's corpse (yes, an actual murder case was solved this way). So it's not so much about the possibility of destroying DNA evidence with chemicals as the impossibility of destroying ALL of it. It would therefore be more practical for a criminal to leave as little DNA evidence that could be traced back to him as possible rather than go out of his way to expend large amounts of bleach trying (in vain) to whitewash the crime scene, the bleach itself being a possible evidence whose purchase could be traced to the offender.
    You've been watching too many episodes of CSI...
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  6. #6
    Chlorine bleach is not terribly effective. However, you might look into oxygen bleach (a common product would be Oxyclean). While it doesn't always completely destroy dna, it does tend to break down hemoglobin and make forensic testing far more challenging.

    https://www.sciencedaily.com/release...0217112516.htm

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  7. #7
    Bleach (sodium hypochlorite) is what DNA processing labs recommend to prevent cross contamination.

    https://www.fsigeneticssup.com/artic...17)30269-X/pdf
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  8. #8
    Oh okay, but what does cross-contamination have to do with it? So if a criminal dumps bleach on a crime scene, it won't get rid of their DNA, but make it impervious to cross-contamination?

  9. #9
    What labs are worried about is the DNA sample becoming cross contaminated (in other words, contaminated with another foreign substance). If that happens, the DNA evidence is declared unusable as evidence, which in a worst case scenario might let a killer walk free. So forensic labs are recommended to use chlorine bleach to clean lab surfaces to make sure nothing can contaminate the DNA sample. In such an example, the contamination area is very small so a solution of at least 10 percent chlorine bleach/90 percent water is strong enough to decontamminate the scene and destroy that tiny bit of possible foreign DNA. However, in most cases where there is a large amount of DNA present (such as the scene of a hatchet murder. Think of blood all over the place), chlorine bleach isn't going to be enough to get rid of that kind of evidence. Oxygen bleach is actually far better at breaking down blood and corrupting DNA, as demonstrated in one article I found: https://www.sciencenewsforstudents.o...ng-away-murder
    Last edited by J Anfinson; June 28th, 2019 at 04:07 AM.

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  10. #10
    Oh okay. Well for my story, as long as the crooks do not bleed on the scene, then they would just have to get rid of whatever DNA might be left of there's that is not blood, such as hair, maybe a drop of spit, etc? Is that right? So is that destroyable, DNA wise?

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