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A common precaution for preparing EtBr-agarose gels is to add EtBr only after the gel solution has cooled somewhat, because EtBr is a dangerous mutagen. Supposedly, adding it to a hot liquid allows EtBr vapors to get into the air and everyone's lungs, where it can act as a carcinogen.

In addition to this are commonly seen special procedures for handling EtBr vials and gels (fresh nitrile gloves, avoid contaminating other work areas, special waste disposal rules).

However, there's also some saying that EtBr isn't all that mutagenic and all this care is over the top.

What's the reality? Just how dangerous is EtBr, especially in amounts used at a typical biological lab? How long does the danger persist? Are even trace amounts hazardous (for instance, touching a "clean" pipette without changing gloves after working with EtBr)?

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    $\begingroup$ I've heard that you shouldn't put EtBr in hot agarose to prevent degrading the dye in the heat. $\endgroup$ – user137 Oct 6 '14 at 23:25
  • $\begingroup$ I also believe you loose intercalate abilities if you break it down with heat. Thus I don't think the risk is vaporized EtBr in the steam. It might be a carcinogen/mutagen given that it intercalates DNA so well, but I think it's toxic effects are more substantiated. With proper PPE you are at little risk. I certainly wouldn't bathe in it. $\endgroup$ – Atl LED Oct 6 '14 at 23:34
  • $\begingroup$ Cows are injected with the stuff in quantities thousands of times higher than are used in a lab without any ill effects. That said, you're probably not a cow, so you might as well wear gloves. Being overly cautious isn't going to hurt anyone, and contaminating someone else in the lab because you're not concerned about what is probably a very low level risk is inappropriate. $\endgroup$ – Jason Patterson Oct 7 '14 at 1:02
  • $\begingroup$ Oh it is not that dangerous as its current image. Pouring hot gel has another problem too; it damages your gel tray and combs. I guess EtBr is not that volatile (MP=260 deg C) that it will fume in a hot gel @ 70deg C. $\endgroup$ – WYSIWYG Oct 7 '14 at 4:24
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I usually find the treatment of Ethidium bromide in the lab widely exaggerates the true dangers of this chemical. It is not really toxic (the LD50 is 1.5 g/kg bodyweight, as a comparision NaCl has a LD50 of 3 g/kg). It has also only been shown to exhibit mutagenic potential to bacteria after it had been treated with liver extracts. This means that some of the metabolized products of EtBr in the liver are mutagenic, but EtBr itself not. See reference 1 for details here. It is also not classified as a cancerogenic substance by the regulation bodies (for example see the National Toxicology Program of the US on Ethidium bromide).

As already mentioned, it is used to cure Trypanosoma infections in cattle (reference 2). Here up to 1 mg/kg bodyweight are given, with no signs of toxic or other adverse effects. The typical concentration used in the lab to prepare gels is 1 μg/ml. It works as a drug by interfering with the mitochondrial DNA (changing it to the Z-form, which is not available for replication). See reference 3 for details. Ethidium bromide also acts as a Topoisomerase I inhibitor as other chemotherapeutic drugs. See reference 4 for more details.

Additionally, EtBr is negatively charged and cannot enter cells or the nucleus, since cannot pass the membranes. I would wear gloves and also apply the usual safety rules when working with gloves (do not touch anything you don't need to touch, especially things like door knobs, keyboards or phones as you might spread contamination) dispose your gloves when not needed anymore and you should be fine.


References:

  1. Detection of carcinogens as mutagens in the Salmonella/microsome test: assay of 300 chemicals.
  2. Comparison of isometamidium chloride and homidium bromide as prophylactic drugs for trypanosomiasis in cattle at Nguruman, Kenya.
  3. A low dose of ethidium bromide leads to an increase of total mitochondrial DNA while higher concentrations induce the mtDNA 4997 deletion in a human neuronal cell line.
  4. The geometry of DNA supercoils modulates the DNA cleavage activity of human topoisomerase I
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    $\begingroup$ The dangers of this compound are wildly exaggerated but like @chris said, the dangers aren't completely known. I wouldn't recommend shaving with it. I think the deep red color actually is what heightens people's curiosities and fears most. $\endgroup$ – rhill45 Oct 9 '14 at 7:36
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    $\begingroup$ I wouldn't recommend this either - and I recommend wearing gloves when handling it. But besides that, irrational fears and actions are really not necessary. $\endgroup$ – Chris Oct 9 '14 at 7:50
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Inspired by Jason Patterson's comment, I looked up "ethidium bromide cattle" and found a blog post about ethidium bromide toxicity. Apparently ethidium is routinely used to treat sleeping sickness in african cattle at 1mg/kg without ill effects. All data concerning ethidium toxicity comes from in vitro tests that may not apply to in vivo use. You should still wear gloves, but don't freak out over it.

The blog post had some references, but most are dead links now. Here is the only working link left. Here's a review article on dye therapy for parasites.

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