Please share experiences of using DEPC reated water?
David F. Spencer
dspencer at is.dal.ca
Thu Mar 22 14:53:47 EST 2001
In article <3aafecbc.239815366 at news.massey.ac.nz>,
E.S.Kwan at massey.ac.nz (Errol) wrote:
> >Although DEPC is considered to be unstable in water solution it does
> >persist at low levels. I DEPC-treated one of my stocks of BLOTTO years
> >ago, immediately after placed it at 65C for considerable time to try to
> >break down the DEPC, and the solution still has that sweet DEPC smell
> >when you take off the cap and sniff it.
> Is it normal practise for you to sniff toxic chemicals? If you read
> the warnings is says to work in a fume hood and wear an approved
> respirator (among other things), so don't you think that you shouldn't
> be sniffing this stuff?
Oh get a grip!
If your lab practices are dictated by a mindless, hysterical reading of
Material Safety Data Sheets (MSDS) you must have a pretty stressful
life. The MSDS for _Tris_ calls for a respirator and working with
mechanical exhaust (not to mention the special gloves and goggles).
Sucrose handling is only slightly less restrictive. If you actually
bothered to educate yourself about DEPC or any lab chemical you'd be
able to make more reasonable choices and not have the audacity to
lecture me (or anyone else) on what is safe and what isn't.
The MSDS has to stretch to embellish the hazard of DEPC by stating that
DEPC can react with ammonia to produce urethane, which in animal studies
is regarded as a carcinogen. Otherwise DEPC is an irritant, to skin,
mucous membranes, etc. Capsaicin is clearly a much bigger "hazard".
DEPC is described at length in a paper by Ehrenberg, Fedorcsak and
Solymosy in 'Progress in Nucleic Acids Research and Molecular Biology'
vol. 16, 1976. The chemistry of DEPC reactions with DNA are well
understood and they are not mutagenic, given that the carbethoxylation
of purines (which occurs only in single-stranded DNA/RNA) leads to
apurinic sites. In addition, the very poor solubility of DEPC in water
coupled with its instability in water, especially in biological
environments containing amino acids in general and histidine in
particular, means that the chance a DEPC molecule could ever _in vivo_
get near a nucleic acid target is insignificant. Your health is at
greater risk while standing in front of a running high speed centrifuge.
You're far more likely to be injured or killed in a molecular biology
lab by physics rather than chemistry.
The MSDS claims that beta-mercaptoethanol is more dangerous than DEPC,
the LD50 level for beta-mercap being less than a third that of DEPC. In
fact according to the MSDS beta-mercap is more toxic than phenol, figure
that one out. And here I've been working with beta-mercap for more than
30 years not realizing I was jeopardizing my life and everyone within
smelling distance. We all know that the real problem with beta-mercap
occurs when you are working with it but the people around you don't know
it and they keep looking at you calling you a pig.
In reality there are relatively few chemicals that constitute a serious
threat in the normal molecular biology lab. I don't snort PMSF, I
wouldn't mouth pipette azide solutions if I worked with them, and I
wouldn't go near acetylaminofluorenes. People have to use some sense
when working with acrylamide, obviously phenol and chloroform, plus less
common things like actinomycin-D. But when you consider how the average
molecular biology lab operates, if there were that many nasty chemicals
lying around then people would be dropping like flies. Frankly I'm
actually surprised that more lab people don't kill or maim/sicken
To return to the original issue which was why people treat water, etc.
with DEPC. With a few exceptions there is no intelligent reason. It is
the same misguided ignorance that prompted someone in this building a
few years ago to autoclave phenol. Fortunately I wasn't the person to
walk into the autoclave room during that brilliant exercise. That could
have resulted in a serious lab mishap caused by strangulation.
And no I can't tell you what DEPC tastes like, but I would imagine
beta-mercap doesn't taste that great. I can only handle capsaicin in
small amounts, in its natural form of course.
David F. Spencer, PhD
Dept. of Biochemistry and Molecular Biology
Halifax, Nova Scotia, Canada
dspencer at is.dal.ca
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