Please share experiences of using DEPC reated water?

[David F. Spencer]

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 
themselves.

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
Dalhousie University
Halifax, Nova Scotia, Canada

dspencer at is.dal.ca