EtBr safety procedures

[BLC]

The tenor of this recent discussion, leading to downgrading of 
the potential risk of EtBr is disturbing and I wish to remind 
contributors that we owe a duty of care, not only to ourselves 
and our students but also to people who come into contact with 
our work without having made the explicit (or implicit) 
Mephistophelian bargain to accept some personal risks in the 
pursuit of science.  Think of the cleaners, for example, in your 
laboratory.

Acridines bind to DNA, by intercalation in some (all?) cases and 
are ptential or actual mutagens.  EtBr can certainly be used to 
stain animal chromosomes (look down the microscope) and it is 
mutagenic in the Ames test with microsomal activation, therefore 
it is a potential mutagen for animal cells.  It is also, 
therefore, a potential carcinogen.  No matter how low the risks 
actually are, laboratory workers should therefore take 
appropriate protective measures.

As departmental safety adviser I have had to consider what advice
to give about these risks and about recommended methods for
handling and detoxification (see Trends in Genetics (1987) Vol
3(11) 308; ibid (1988) 4:89; ibid (1990) 6(2):31; Biotechniques
(1990) Vol 8(4) 372-3.).  In my view, one of the significant 
risks to laboratory and associated workers is that dried deposits 
of EtBr may become mobilised as dust particles and inhaled, to 
give a high very local dose to lung tissue.  For this reason my 
departmental code of practice requires EtBr-stained gels to be
washed (twice, 10 mins each time) in water or buffer before being
transferred to a transilluminator and the transilluminator 
surface and surroundings to be washed and dried with absorbent 
paper after use.  All potentially contaminated material goes to 
incineration.  The disposal of concentrated EtBr wastes and the 
decontamination of spills and splashes (use a hand UV-lamp if you 
think they do not exist!) are dealt with by methods derived from 
the references listed above.

Detoxification with bleach is definitely not recommended.

In an earlier Message, Bickle wrote  to the effect that Activated 
EtBr scores just above background in the activated Ames test.  
This disagrees markedly with the report by Bensaude (1988) TIGS 
4:89 that it is 10-fold more mutagenic (for yeast) than NTG and
5-fold more mutagenic than benzo-(a)- pyrene.

I hope to see strong support for this conservative approach to 
EtBr safety procedures.  Better safe than sorry.

Bernard Cohen
Genetics Dept
University of Glasgow
Scotland.