Re: Slug & Snail / Can they digest PCB toxins?

David,

PCBs are certainly problematic pollutants because they are so resistant to
degradation by natural processes (photolysis, microbial breakdown, etc.) in
the environment.  They are also very fat soluble and so are readily
absorbed into animal tissues, especially fat, where they stay for very long
periods of time.

Animals don't actually "digest" PCBs.  Digestion is the term specifically
used to describe the process of breaking down foodstuffs into smaller
particles that can then be absorbed by the digestive tract.  Rather,
animals metabolize PCBs (and other toxicants) using enzymes.

Animals have enzymes (especially in the liver & kidney) whose job it is to
chemically alter foreign substances so that they are more easily excreted.
 Basically, the goal is to make substances that need to be excreted more
water soluble because then they will stay in the blood and be filtered out
by the kidney.  If the resulting substance (metabolite) is relatively large
in size, it will be excreted via the bile & eliminated in the feces. 
Either way, the idea is to increase water solubility.

Fat soluble substances, like PCBs, preferentially deposit in fatty tissues.
 Because these tissues are not very metabolically active, the substance
sticks around for a long time.  They need to undergo chemical alteration to
faciliate excretion (by keeping them out of the fatty tissues and in the
blood).  Some animals are much better at doing this with PCBs than others.
 Basically, it has to do with the types of enzymes that the animal has. 
Enzymes are proteins which are coded for by genes.  So, animals with
different genes will have different enzymes (or forms of an enzyme).

While I am not aware of specific reports of snails or slugs doing a better
job of metabolizing PCBs as compared to other snails or slugs, it would not
surprise me.  There are many species of these mollusks and some are bound
to be better at eliminating these compounds than others.  The organisms
that are able to metabolize these compounds would be beneficial in areas
where these compounds are found because they would help faciliate the
removal of these substances.

So while I can't say that what you heard about estuarine snails has been
confirmed scientifically, I can say that it is quite likely that such
animals exist.

Thanks for your question.

Sue