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Shell toxicity


Sorry it took so long to get back to you all on this=85I decided to
read up a bit first, and check on facts with a former co-worker.

I was starting to seriously make jewelry while still working in the
Mollusc division of the Field Museum in Chicago. Some of my first
pieces involved Paua Shell. I remember asking my boss, the Curator
of Invertebrates, if I need take any special precautions. He replied
that as the dust is a minor irritant, to wear a dust mask, and wash
my hands afterward (I was grinding the shells). He said there was no
special toxicity involved.

I=92d ask him more detailed questions now, but he died 12 years ago.
(heart attack, not shell exposure!)

It=92s a dramatic phrase, =93If it once lived, it can kill you=94; but=
not sure how much I believe it. That would describe all our
food-both animal and vegetable. Ground shell is fed to chickens, and
found in other animal feed. It=92s a cheap and more digestible source
of calcium carbonate than mineral sources such as dolomite (calcium
magnesium carbonate). Have you seen all the recent hoopla about
=93coral calcium=94 as being supposedly better for you than other form=
of calcium carbonate? (I don=92t believe that either…just what the
world=92s coral reefs need now, another reason to destroy them!) Of
course, limestone is also calcium carbonate, and it comes
from:…what else, shells deposited in ancient sea beds.

So anyway, I=92ll quote from one of my boss=92s few books written for
laymen, on shell structure.

=93The…molluscan shell…consists of an outer covering, the
periostracum, which is composed of organic chemicals and several
inner layers of calcium carbonate…(in the shell)the calcium
carbonate crystals are laid down in an organic matrix, deposited
either as calcite or aragonite…layers of calcite and aragonite may
alternate…different angles of deposition presumably serving to add
strength to the shell itself.

My note: the periostracum is usually a dull brown and flaky layer on
sea shells. It sheds readily after the animal=92s death, and whatever
remains is usually ground off by whoever harvests the shells.
=93Pretty shells=94 are not very pretty until this layer is removed. I=
life it serves as protective coloration, and protects the animal
from shell erosion and boring organisms.

=93Most familiar is the sometimes brilliant inner surface of such
shells as abalones, chambered nautilus, and (etc). The =93mother of
pearl=94 shell layer in these taxa consists of very fine layers of
aragonite . . . deposited parallel to the shell surface. The
crystals are deposited in plate form, producing an extremely
polished surface.=94

From The Shell Makers, by Dr. Alan Solem

You may be thinking of the dust as being dangerous in the same sense
that diatomaceous earth is dangerous; the skeletons of the diatoms
(simple one- celled protists) being extremely minute and extremely
sharp, and likely to cause severe irritation to eyes, mucous
membranes, etc. These are made of silica. (People sprinkle
Diatomaceous earth (essentially just dead diatoms,) in their gardens
to kill slugs: the sharp-edged diatoms penetrate through their
protective slime coating, cut into their soft skins, and the slugs
dry out and die.)) This is not the case with shell dust: the
crystals are not sharp, and they are not silica. I remember this
question coming up at work. (People were always calling to ask how
to kill slugs, which are also mollusks, just without a visible
shell.)We were always told to warn people about the potential
irritation from using diatomaceous earth, and use beer to kill the
slugs instead. (now that=92s another story . . .)

Of course, what applies to shells also applies to pearls (and pearl
dust). If you ever drill pearls, you know about the fine dust. I=92m
not keen about using shells (I=92ve been, I suppose you could say,
psychologically over-exposed), but I do use pearls. I wear an
ordinary, well-fitted dust mask, wash my hands, and wipe down the
tools and bench afterward with a damp towel. Mother-of-pearl and
pearls are the same material, calcite and aragonite in an organic
matrix. Shells with a dull finish have just more calcite than
aragonite. Calcite is also more stable over time, while aragonite
breaks down: which is why shells found in archaelogical sites have
often lost their luster. . . .and ancient pearls look dull!

I=92m not sure, but I imagine that people who are allergic to
shellfish (molluscs, not crustaceans: much less common allergy)
would also be allergic to the shells: to the organic constituent,
which is largely proteins. Waste products from the animal=92s food are
also excreted into the shell: that accounts for the color. Lovely,

You can find face powder and lotions (supposedly) made from ground
pearls in Asian grocery stores (most likely ground shells, not

If you are still worried, the next stop is OSHA.

For those who are interested, in a separate posting (this one is
already too long), I=92ll write about Dentalium shells. Hope this

Lin Lahlum