[NHCOLL-L:1893] RE: Propyl- and Ethyl alcohol preservatives

[Simmons, John E]

There really isn't a "correct procedure" for doing this, but based on what
has been done, I recommend staging between fluids to avoid too much stress
to the specimens.  What steps you use will depend in large part on what the
concentrations of the ethanol and isopropyl are.  Below is a section from
"Herpetological Collecting and Collections Management" that addresses this
issue.

--John

John E. Simmons
Collection Manager, Natural History Museum
and
Coordinator, Museum Studies Program
University of Kansas
Dyche Hall
1345 Jayhawk Boulevard
Lawrence, Kansas 66045-7561
Telephone 785-864-4508
FAX 785-864-5335
jsimmons at ku.edu
www.ku.edu/~museumst/



Selection of a Preservative
Since the mid-1600s, when the preservative properties of spirit of wine were
discovered, the overwhelming favorite fluid preservative has been ethyl
alcohol, usually in a 60-75% concentration.  The second most common
preservative (though far less common than ethyl alcohol) is isopropyl
alcohol, which is less expensive and easier to obtain.  Isopropyl alcohol
was not used as a preservative until sometime after 1920 when commercial
production of it began (Hatch 1961); thus, we have fewer than 80 years of
experience with it as a preservative.  The third common preservative is
formaldehyde, which was not used as a preservative until sometime after 1893
(Simmons 1995).  Methyl alcohol (wood alcohol) is unsuitable for use as a
preservative.  

The biggest drawbacks to ethyl alcohol are its expense, the necessity of
obtaining a Federal permit to purchase it tax-free, and the potential fire
hazard it poses.  The arguments in favor of using isopropyl alcohol are that
it is less expensive and easier to obtain (a Federal permit is not
required), and that it leaves the specimens more flexible (Walker et al.
1995).  However, there are many more arguments against its use.  Isopropyl
alcohol poses a fire hazard, it is twice as toxic as ethyl alcohol, and many
people find its odor objectionable.  The greater flexibility of the
specimens may mask warning signs of deterioration.  Isopropyl alcohol does
not have the 350+ year record of use in museums that ethyl alcohol does.
The use of isopropyl alcohol as a preservative makes specimens unsuitable
for most types of histological preparation (Jones and Owen 1987).  It is
difficult to measure the density of isopropyl alcohol solutions,
particularly with a hydrometer, as its density is close to that of water.
In low concentrations (below 45%), isopropyl may promote a rapid clearing of
tissues.  Isopropyl alcohol is difficult to mix with water and prone to
layering in containers (Fink et al. 1979).  In long-term storage, it has
been shown to soften bone (Steedman 1976).  While perhaps an argument might
be made to continue using isopropyl alcohol for fish collections already in
it (Walker et al. 1995), the argument does not justify using a preservative
other than ethyl alcohol to preserve herpetological collections.

Just because most fluid preserved collections use ethyl alcohol does not
mean that it is the best preservative to use.  However, no data indicate
that any other preservative is superior, or even the equal of ethyl alcohol
(Simmons 1995).  Some alternate preservative formulas have been proposed for
specific functions, such as preserving colors of specimens (see Color
Preservation), or making specimens useful for specific histological
techniques.  A few substances, such as phenoxetol, were in use for a decade
or more before preservation problems were detected (Crimmen 1989).  In the
absence of carefully controlled, long-term or accelerated aging studies of
other preservative solutions to demonstrate their superiority, fluid
preserved specimens should continue to be kept in ethyl alcohol.

Transfer of Specimens from Fixative to Preservative
It has long been customary to remove specimens from the field fixative,
rinse or soak them in water in open containers (sometimes for several days),
and then place them directly in storage-strength alcohol preservative
(Simmons 1995).  There are several problems with this procedure.  Damage may
result from soaking specimens too long in water.  Once formaldehyde is
replaced with water, enzymatic activity in the tissues may resume (Taylor
1981a) and the water may reverse the chemical crosslinks, permitting
autolysis to occur.  Specimens will swell as they absorb water during
rinsing or soaking and shrink once they are placed in an alcohol
preservative solution.  Some workers have suggested transferring specimens
directly from the formalin fixative solution to the alcohol preservative
(Fink et al. 1979).  This procedure has several drawbacks, including severe
osmotic shock in going from nearly 100% water to 30% water, and the quantity
of formaldehyde that is released into the alcohol preservative.
Formaldehyde in the preservative will drive the acidification of the alcohol
solution, which will decalcify specimens and cause more severe color
changes, as well as pose serious health risks for people working with the
specimens.

Based on the studies available on shrinkage, swelling, and other effects on
specimens during transfer (e.g., Jones and Owen 1987, Lafromboise et al.
1993; see discussion in Simmons 1995), and considering the effects of
osmotic pressure changes on tissues (Steedman 1976), a more gradual transfer
of specimens from a solution of near 100% water (e.g., "10% formalin") to
30% water (70% ETOH) is recommended.   Because osmotic pressure rises
steadily with ethanol concentrations below about 75%, it has been suggested
that approximately equal concentration increments are the most appropriate
for stepping specimens up to higher ethanol concentrations (Waller and
Strang 1996).  Following the protocol of Laframboise et al. (1993), I
recommend using steps of approximately 20% to stage specimens from 10%
formalin solutions to 70% ethyl alcohol (Figure 9).

Transfer of Specimens between Alcohols
Specimens should not be changed from one type of alcohol to another,
especially specimens on loan from other institutions.  Changing a specimen
from one type of alcohol to another, particularly from isopropanol to
ethanol, may cause significant shrinkage and other damage (Jones and Owen
1987) and significantly alter the body proportions of the specimens (see
review in Simmons 1993).  If it is necessary to change specimens from one
alcohol preservative to another, follow the protocol of Laframboise et al.
(1993).

Laframboise, S., R.M. Rankin, and M.M.L. Steigerwald.  1993.  Managing
change: alcohol transfer at the Canadian Museum of Nature.  Pp. 28-33 in
Snyder, A.M. (ed.).  The 1992 American Society of Icthyologists and
Herpetologists Workshop on Collections Care and Management Issues.  ASIH.
52 pp.

-----Original Message-----
From: Vusi Mthombeni [mailto:V.Mthombeni at ru.ac.za] 
Sent: Tuesday, April 15, 2003 1:50 AM
To: NHCOLL-L at LISTS.YALE.EDU
Subject: [NHCOLL-L:1886] Propyl- and Ethyl alcohol preservatives

Dear NHCOLL list members,

I would like to know what is the correct procedure to transfer specimens
which 
were originally preserved in propyl alcohol into ethyl alcohol or vice
versa. 

Thanking you in advance.

Vusi Mthombeni
Collections Officer
South African Institute for Aquatic Biodiversity
Private Bag 1015
GRAHAMSTOWN
6140
SOUTH AFRICA

Tel: +27 (0)46 6035800
Fax: +27 (0)46 6222403