Does using too much alcohol affect specimens?
If you have ever seen a pristine eyeball or a deceased creature preserved in a glass jar at a laboratory or museum, you likely know about the remarkable preservation capabilities of alcohol. The official name for this technique is liquid preservation. Scientists have relied on it since the 1600s to preserve specimens. When done correctly, it can maintain a specimen for hundreds of years.
Professor Bill Carroll at Indiana University in Bloomington explains: “In simple terms, alcohol acts like a poison to microorganisms that cause decay.” For example, an alcohol concentration of about 14% in wine can help delay bacterial growth for many years (many types of wine also contain additional preservatives like sulfur).
A preserved hammerhead shark at the Natural History Museum in Berlin, Germany.
But how does this method work? Katherine Maslenikov, the fish collection manager at the Burke Museum in Seattle, states that preserving other organic materials, such as DNA, tissues, or even whole animals, requires a higher alcohol concentration.
For instance, Maslenikov can take a fish sample, remove some tissue samples for DNA analysis, and inject formalin (a solution of formaldehyde gas dissolved in water) into the fish to halt biological processes within, such as enzyme reactions and tissue degradation.
She can then immerse the fish sample in a 70% alcohol, 30% water solution. For long-term storage, 70% seems to be the magic number.
Maslenikov states: “There is enough water in the solution for the tissues to be hydrated, helping the animal or specimen maintain its shape, while there is sufficient alcohol to prevent mold and bacterial growth.”
Higher alcohol concentrations, such as 95% ethanol, act as a dehydrating agent, meaning it removes and replaces water in cells, tissues, or whole-body samples with alcohol.
The lack of water causes changes to water-sensitive proteins. They unfold or deform and harden in adjacent positions, fixing the shape of the specimen.
According to a 2013 study published in PLOS One, this technique is a common way to preserve DNA.
It can be challenging to decide the percentage of alcohol to use. Too much or too little can affect the shape and pliability of the specimen or even diminish the specimen’s preservation capabilities in the solution.
High alcohol concentrations used for dehydrating specimens will preserve that specimen. However, Maslenikov notes that this process can also cause the specimen to shrink (due to dehydration) and become brittle (due to proteins hardening). Sometimes that’s okay; it all depends on what you’re trying to preserve. Meanwhile, a specimen can deteriorate quickly if it retains too much water.
“If an organism has enough water in its tissues, it can dilute the alcohol. If this happens, the alcohol concentration may not be strong enough to kill any lurking microorganisms that may hide deeper within the specimen, somewhere like the intestines of the whole animal. Any missed bacteria can decompose the specimen. This is why it is important to change the alcohol about 24 hours after immersing the organism, as it increases the alcohol concentration of the solution,” says Christopher Rogers, an associate professor at the Center for Ecological Research and Survey at the University of Kansas.
When it comes to using alcohol as a preservative, Professor Carroll states that the appropriate alcohol concentration will help inhibit microorganisms without destroying the cellular structure of the specimen.
