Quantcast
Skip to content

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. Craig on May 10, 2019 at 8:24 pm

    Great article! Helps tone down my paranoia a bit when working with it. I’m afraid I’m going to kill people if I’m not careful.

  2. Ariwa99 on May 16, 2018 at 7:12 pm

    Hi, can anyone tell me the half-life of ethidiumbromid under standard conditions ? and can the half-life vary under difference conditions ?

    • Dr Amanda Welch on May 21, 2018 at 4:37 pm

      I’m not sure. But the EtBr from my grad school lab was at least a decade old.

  3. Sudharsan on June 23, 2017 at 12:09 pm

    is acute exposure to ethidium bromide dangerous? is its carcinogenicity time tested?

Leave a Comment

You must be logged in to post a comment.

This site uses Akismet to reduce spam. Learn how your comment data is processed.

Scroll To Top
Share via
Copy link