There exists a less toxic chemical than EtBr to stain DNA: SYBR safe
DNA stain (a fluorescence dye sold by a certain vendor).
SYBR Safe is about 10X less sensitive though.
I suspect that not many chemicals in the lab are less toxic/mutagenic than
EthBr. The classic Ames test shows that 5 ug of EthBr results in 1012
revertants. In comparison, condensate from a smoke of a a single cigarette,
in comparison, gives almost 20X more revertants (18200, Table 1 in: PNAS,
1975, 72(12):5135. Detection of carcinogens as mutagens in the
Salmonella/microsome test: Assay of 300 chemicals").
Assuming linear relationship, it means that one has to eat about ten mini
agarose gels (20 ml at 0.5 ug/ml each) to get approximately the same
mutagenic effect as smoking a single cigarette. :-)
Additional reason why EthBr is probably completely harmless to humans at
concentrations that we use it is the fact that it is so hydrophilic that it
cannot pass plasma and instead is very quickly cleared from the bloodstream
by kidneys.
- Dima
