Ethidium bromide carcinogenicity?

Curt Ashendel ashendel at
Thu Apr 13 11:32:09 EST 1995

On 13 Apr 1995 02:52:53 GMT, 
Scott Bruce Mulrooney  <mulrsb at> wrote:

>: The question has come up in my lab again about the possible risk of
>: exposure to Ethidium bromide.  I've heard statments to the effect that
>: exposure is harmless; that it is used in Australia as a "sheep dip" to
>: kill parasites but that the sheep are unharmed; that smoking is a
>: hundredfold worse for you than exposure to EtBr.  What's the current
>: status of this argument?  Any information would be appreciated.
>I always assumed that Ethidium Br was considered harmful - the bottles
>always said "carcinogen" on them. I think something that sticks to
>DNA so well can't be good.
>I once looked up the earliest papers on ethidium br: the first one
>published was in the 1950's. It seems the Boots Drug Company in
>England was synthesizing ethidium br, propidium iodide and some 
>others to use as a drug to kill trypanosomes in cattle!

Our bottle says "Possible Mutagen". I do not think EtBr is a carcinogen. 
Mechanistically, EtBr is at worst a frame-shift mutagen, and this is the 
one class of mutagens that is nearly always non-carcinogenic (probably the 
toxic effect of multiple frame shifts exceeds the probability of 
selectively knocking out tumor suppressor gene.) AFAIK, there are no data 
indicating EtBr is a carcinogen in any species (can anyone quote the  MSDS 
on this?) However, I believe it is a weak mutagen for bacteria and possibly 
for animal cells. It has a very low efficacy however, because it binds to 
protein much more strongly than to DNA. Since skin exposure to EtBr results 
in nearly complete binding to the protein in the dead squamous cells  of 
the skin, which are lost quickly through sloughing, it really is not all 
that dangerous a compound.  I would say that a 3 Kg gallon bottle of 
concentrated HCl is far more dangerous.

However, some caution is always a good idea: Wear glove when working with 
high concs of EtBr and wear a lab coat when working with concentrated HCl.

Personally, I don't wear gloves when working with dilute solutions of EtBr 
(such as in gel buffers and pouring gels).

Just my $0.02 worth.

Curt Ashendel
Purdue University
West Lafayette, IN
ashendel at

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