[NHCOLL-L:3042] RE: shipping in propylene glycol (Re: EtOH blues)

[Dean Pentcheff]

I'm worried about some of the strategies that are being suggested for
obtaining propylene glycol as a shipping substitute for alcohol.
Specifically, I'm concerned that the unknown additives in consumer-grade
propylene glycol may be destructive to specimens.  

A important quality of alcohol preservation (rather than formalin) is
that it facilitates molecular genetic analysis.  Extraction and
amplification of DNA is a delicate chemical procedure that can easily be
inhibited by a broad range of chemicals.  It may be that propylene
glycol doesn't damage DNA or interfere with molecular analysis.  That
may not be true of the proprietary additives that are in consumer
mixtures of propylene glycol (antifreeze, etc.).  We have no way of
knowing how the (unspecified) brew of additives will affect analysis.  I
don't think it's a good idea to contaminate specimens that way.  Even if
the present user of the specimen doesn't intend molecular analysis, it's
entirely possible that a future user may.

Of course, there is the issue of cost.  Institutions may be unable to
afford reagent-grade propylene glycol, just as they may be unable to
afford proper hazmat shipping of specimens in alcohol.  I don't see that
as a justifiable reason to use contaminated propylene glycol for
shipping.  Preservation of specimens' scientific utility must be the top
priority.  If that means the specimens can't be shipped, then they can't
be shipped.  The decision to put a specimen in a solution with unknown
additives should be approached the same way as a decision to permit
destructive sampling: it should be considered only in rare circumstances
since it has the potential of removing future utility of the specimen.

What this all suggests to me is that it would be productive to:

1) establish that propylene glycol really is a non-destructive and
non-interfering chemical when involved in molecular genetic analysis of
tissue (established by proper controlled experiments, not one or two
anecdotal reports that it worked for one or two specimens); and

2) if so, find a cheap source of sufficiently pure propylene glycol for
shipping purposes.

Because we'll never know what the proprietary additives are in consumer
propylene glycol (and they can be changed at a manufacturer's whim), I
don't think that source will ever be practical.

-Dean
-- 
N. Dean Pentcheff
dean at crustacea.nhm.org