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Ethidium Bromide: A Reality Check

face.jpgThe hysteria among molecular biologists about our old friend ethidium bromide has long been an irritation to me. Researchers are rightly wary of this potential carcinogen. More recently this wariness has been whipped up into a witch hunt by companies touting “safer” alternatives and disposal methods. While I don’t for a minute think that we should all throw our gloves away and bathe in the stuff, I think that it’s time for an informed reality check about the dangers, and the myths about ethidium bromide.

etbr.pngEthidium bromide is genotoxic, a frame-shift mutagen and teratogen. This is fact, determined by in vitro tests on various cultured cell lines and embryo systems that showed ethidium bromide can cause things like frame-shift mutations, chromosomal recombination, arrested cell division and developmental problems. This information is summarized in an excellent report from the National Toxicology Program.

These in vitro tests, which comprise the entire body of evidence upon which the ethidium bromide hysteria is built, don’t provide any evidence that ethidium bromide can exert a genotoxic effect in anything more complicated than a single cell or an unprotected embryo. In fact there is no direct evidence implicating ethidium bromide as a carcinogen in any animal.

For many years, ethidium bromide has been routinely administered for the treatment of African Sleeping Sickness in cattle. For this purpose, ethidium bromide is administered via subcutaneous or intramuscular injection with no reported increase in incidence of tumor formation or birth defects in the treated cattle. This suggests that ethidium bromide is far less genotoxic to animal systems than is presumed from the in vitro data.

The recommended, apparently non-toxic, dose of ethidium bromide is 1mg/kg of body weight in cattle. In comparison to this, the standard concentration used in molecular biology (around 1 microgram/litre), is low. Rosie Redfield puts it into perspective:

A 50kg researcher would need to drink 50,000 liters of gel-staining solution to get even the non-toxic dose used in cattle.

From this, the risks posed to a scientist handling a very weak solution of ethidium bromide, with a gloved hand (remember the cattle are injected with the stuff) are put into perspective.

A real concern is that the irrational and ill-informed fear of ethidium bromide drives us to solutions that are more dangerous than ethidium bromide itself. What could be more dangerous than ethidium bromide?

  • More concentrated ethidium bromide. The method of choice for ethidium bromide disposal at the moment seems to be absorption onto charcoal followed by incineration. You have a 1 microgram/litre solution of ethidium bromide, a concentration that appears to be of low toxicity according to the data from cattle. To me, it seems counter-intuitive to make it MORE concentrated by absorbing onto charcoal. What about just diluting it in water, reducing the toxicity even further?
  • More toxic reaction products of ethidium bromide. Another disposal method is to react it with phosphoric acid, HCl, bleach… but these are fairly dangerous chemicals themselves, and can produce reaction products that are even more toxic than ethidium bromide itself.
  • Safer DNA dyes. Beware of clever marketing and don’t believe everything you read. For example, as Rosie points out in her excellent article, “SYBR safe” has a higher acute toxicity in mice than ethidium bromide.

My take home message on this would be to forget all of the hype and myths you have read about ethidium bromide, get real and do what a scientist does best; read the articles I have cited, arm yourself with the known data. Then make your own decision on how to handle ethidium bromide, a decision based on fact… not hysteria.

As always, your comments are welcome!!

33 Comments

  1. yaseen on May 17, 2017 at 11:21 am

    hi…. i got a cut on my finger with blade while i was cutting etbr gel….. i am panic about the incident….. wat precautions do i need to take.. please respond..

    • Dr Amanda Welch on May 17, 2017 at 2:33 pm

      Hi Yaseen,
      My suggestion is to contact Environmental Health & Safety at your institution. It’s best to get their opinion on this.
      Best wishes,
      Amanda

    • Tushadri singh on July 17, 2018 at 11:16 am

      Hi! The same happened with me today yaseen.
      Please tell me what to do?

  2. Thiago Marques on May 10, 2017 at 11:05 pm

    Hi! Anybody know the article about low toxicity of the ethidium bromide, please? I would want to read.

  3. James on April 20, 2017 at 3:21 am

    When I was an undergraduate, I worked in a Cell and Developmental Biology lab as a federal work study student. Aside from cleaning and restocking solutions, I regularly prepared DNA mini preps using gel electrophoresis. At the time, I was an 18-year-old with little knowledge of molecular biology and, on a few occasions, removed broken gels from the solution that had been cracked by inserting or removing a comb. After 18 years, I have not noticed any visible effects, but have wondered if I may have caused damage that will manifest later in life.

  4. HANDE ASIMGIL on April 19, 2017 at 9:56 am

    i HAVE DISPUTE ABOUT ETBR TOXICITY IN THE LAB. I WANT TO SHOW THEM THE PAPERS BUT I CANT REACH THEM. WOULD YOU SEND IT TO ME PLEASE? THANKS.

  5. VINCENT on November 10, 2016 at 12:17 pm

    Hello,

    Did they also do long term studies about the effect of Ethidium bromide? Because you could suspect that there might be an effect for people working 40years with it?

  6. elly on September 22, 2016 at 10:54 am

    hi
    I have question about half time ethidium bromid please answer me

    • Dr Amanda Welch on September 22, 2016 at 1:11 pm

      Sure! What’s your question?

  7. No2 dg on October 12, 2015 at 2:35 pm

    Unlike Argent23 in my current lab, we have a bunch of those with EB paranoia. I just can’t help to wonder…How long has EB been used in labs worldwide for molecular biology, DNA staining etc? Since the 60s maybe. And how many of those researchers suffering from EB-related disorders? I really can’t find any number.
    We just need to use it with precaution and take care of the disposal properly just like most hazardous lab material and there are quite some.

    • GJN on September 20, 2018 at 11:24 am

      Our lab technician and her peers, and many others I know, used to handle EtBr gels without gloves for decades. I would not recommend this, please use gloves, but they are all fine. It does not penetrate tissues well. It is easily inactivated with chlorine bleach. It is used at fairly low concentrations in the gel, etc.

  8. hitarth changani on July 12, 2015 at 12:27 pm

    Hii,

    This is really very important article. This is help all the molecular biologists during their experiments. For further little confirmation, I need all the references concluding this article. Can i get it?

  9. Dill Huang on September 27, 2012 at 11:29 pm

    EtBr has been successfully used to generate rho0 cells that have no mtDNA, it works because ethidium cannot effectively enter the nucleus. There has Always been concerns that ethidium may interact with genomic DNA but there has been no evidence for that so far in the case of rho0 cells. A lot of the acute toxicity is probably due to mitochondrial toxicity than actual mutations.

    My lab have ceased to use ethidium bromide because the taboo associated with it is simply too much to handle. Many proprietary EtBr replacements are just as dodgy, I know a few are spiked with acridine orange which is a confirmed carcinogen way way worse than EtBr.

  10. Judith R. Brouwer on May 15, 2012 at 8:30 pm

    Thanks, that is very interesting and helpful.
    I like perspective!

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