Oyster Shells and heavy metals


Dec 20, 2015
I'm new here, so please forgive me if this topic has already been covered. I looked first but didn't see anything.

For many years, I have been reluctant to feed my chickens oyster shells because of where they come from. That is, oysters come from bays and estuaries, which is also where heavy metals end up being deposited. It's not that I've ever heard that oyster shells are laced with heavy metals, I just assume they are given the environment they live in.

I give ground granite for grit, but haven't found another source of calcium. So I just feed a good laying mash and scratch grain.

Am I all wrong about oysters and heavy metals? Does anyone know of another source for calcium?

My birds always lay well and I've never had trouble with thin egg shells, so maybe it's a moot point.




BYC Staff
Premium Feather Member
5 Years
Jul 16, 2015
You need to check the source of the calcium in your layer ration, it might actually be from oyster shells. When fed mostly layer ration, hens won't actually need or eat much oyster shells. You could also feed them back their eggshells for extra calcium.

Pork Pie

Premium Feather Member
6 Years
Jan 30, 2015
My understanding is that shellfish are good bio-accumulators of heavy metals. Having said that I can only assume that oyster shells are a by-product of human consumption and they would not be harvested from sites high in pollution. Nothing to sweat imo.



Chicken Juggler!
Premium Feather Member
8 Years
Nov 27, 2012
SW Michigan
My Coop
My Coop
I've often wondered.....where does that crushed oyster shell come from??? <scratcheshead>

Is it a byproduct of oysters harvested for humans?
Where do those oysters come from....farmed or wild harvested?
What is in either environment that might remain in the shells?

Hard enough to pinpoint the sources of most human foods, let alone livestock/pet feeds.


In the Brooder
Aug 8, 2016
Northern IL
Oyster shell does contain some heavy metals (although less than the soft tissues). Many of these metals do bioaccumulate, and chickens are small, so toxicity level doses would also be small for them. You can rinse, bake and pulverize their own eggshells and periodically add to feed. You’ll see extra surface deposits if it is too much. Much of your feed already has calcium, so you do not need a lot.

Folly's place

9 Years
Sep 13, 2011
southern Michigan
We all do our best to eat right, do healthy things, and manage our animals the best way possible. Saying that, I'm not going to fret about the oyster shells that my birds eat.
Blinders on, maybe, but there's too much else to be concerned about!
Any university or other studies on this? Has anyone cared to research it? That's an interesting thing to find out.
We all likely have other opportunities to ingest and be exposed to heavy metals, especially living with lead paint, etc. Most of us do okay most of the time anyway, fortunately.

Al Gerhart

9 Years
Sep 29, 2011
Oklahoma City
Uh, most granite also contains heavy metals so you might want to look at that if you are concerned that much. Back between 2005 and 2009 I was doing some research on granite countertops and wound up with one heck of a bunch of bored scientists friends coming from uranium processing, nuclear safety, grinding abrasives industry, and the radon remediation industry. Actually was co author on several published studies presented at conferences. We were cranking away researching the uranium content when a dude that made his living as a uranium geologist mentioned "Uh, you do know that uranium is just one of the radioactive elements and there are dozens of heavy metals present, both radioactive and stable?". No I didn't know....

So I ran a ton of 12 x 12 granite samples up to Boulder Colorado to a man that had an XRF gun, looks like a hand held radar gun, spits out a list of heavy metals present in what you point it at. Yikes, lead, arsenic, cadmium, chromium, lots of uranium, and dozens more heavy metals. Everything except beryllium. Finding beryllium was the Holy Grail but my budget was limited to a hundred scans so we didn't find that one.

Amounts varied of course from small trace amounts to ore quality, as much as 1% of some heavy metals, much more for common metals like lead.

Is it a danger? Heavy metals have to be in the right state to be bio available, sometimes that can be done by water, oil, PH levels, many factors. Consider the short life of a meat bird that might not have the time to accumulate much versus an old layer that was an eating machine for three years till she went to the stew pot. Also consider that you are more likely to become room temperature in a car wreck before you die of heavy metal poisoning.


Chicken Juggler!
Premium Feather Member
8 Years
Nov 27, 2012
SW Michigan
My Coop
My Coop
an XRF gun, looks like a hand held radar gun, spits out a list of heavy metals present in what you point it at.
Used one of these at work for metal composition on stn stl...take a few samples of your yard dirt to him, along with a handful of granite grit and oyster shell for birds.

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