Fishes and benthic invertebrates are often preserved in alcohol and/or formalin/formaldehyde for future identification and sorting, compiling very large historical libraries. Does anyone know if these preservation techniques affect the tissues heavy metal concentration?
Dear Durate
It all depends on the temperature of preservation and also the duration of preservation.
Just to check experimentally, may depend on volume, type of material etc. + obvious temperature-duration etc. Diffusion-how the ions are bound-etc. bla-bla-bla.
Frequently heavy metals bind to sulfhydryl proteins in biological tissues and the binding is pH sensitive, with metal dissociation occurring in low pH conditions. Often old formalin preserved samples might be suspect because they often did not use a chemical buffer in combination with the formalin and over time some of the formalin oxidizes to formic acid lowering the pH. Likewise, there may be oxidation of ethanol to acetic acid over time as well. Looks like you better proceed carefully.
Yes, there is evidence that a variety of heavy metal concentrations in biological samples can be influenced by preservation. I believe a PhD student of Linda Campbell's (John Poulopoulos at Queen's University, Kingston, Ontario, Canada) did some work on this, looking at how mecury and other element concentrations, as well as stable isotope values, are affected by preservation techniques.
It is a special study then. For measuring heavy metals it is better to start with fresh material unless having specific aims with the preserved unique specimens. It could be interesting to compare nowadays with older times, but preservation techniques might be different. Also we do not know if the preservation liquid was changed carrying away the heavy metals, e.g. I know some brave people used preservation ethanol for unusual purposes and it had to be refilled later.
Yes, the preservation chemicals affect the heavy metal concentration, but it all depends upon the type of chemical and heavy metal present.
Dear Bernardo;
have you got the answer for your question? Kindly share it please
This is a very interesting discourse. I want to believe that preservative agents cannot affect the concentration of heavy metals in sample. The only thing I think can happen is biotransformation of the heavy metal in the sample but total concentration cannot be increase or reduced by chemical agents. Well, I am subject to correction pls.
Yes preservation will affect metal concentration in tissues. As stated before, the main issue would be a change in pH. A non-buffered formalin will lower the pH of the preserving medium and a large portion of heavy metal would have been extracted from the biological sample into the preserving medium. You might possibly analyse both the tissues and the preserving liquid to recover most metal. However you wouldn't be able to rule out a external source of contamination of the preserving chemical (i.e. using low grade regents or contaminated labware). Plus you wouldn't know if the preservation liquid had been changed at some point in time, flushing away most of heavy metal. Basically unless you have preserved the samples yourself and trust no external contamination or change of medium has occurred, I think there is simply too many uncertainties with this method to extract any useful information.
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