Shellfish shells as bio-accumulators of heavy metals

I've held a suspicious eye towards oyster shells as a source of calcium and magnesium for our chickens, mostly because of shellfish farming practices. We've still given them free choice because they seemed to be a better alternative to the mining of limestone or the labour and of baked & crushed egg shells.

Just read a story of a Toronto artist who has debilitating heavy metal poisoning from working with mussel shells for years without a respirator.

https://www.dailymail.co.uk/news/article-6450071/Toronto-sculptor-59-gets-heavy-metal-poisoning-spending-15-years-mussel-shells.html

What are your thoughts on limestone vs. eggshells?

Oh my goodness, I hadn't even heard about that. We do oyster shell for our ducks, as well as giving them back their eggshells. But, there's never enough eggshells, so I have to supplement that with other sources of calcium.

Are limestone and oyster shells the only sources of calcium for poultry?

I would be very interested to know if the shells accumulate, I give them to my chickens, and I have health issues that tie into heavy metal poisoning, although I've had that for years, not just since I got chickens.
REALLY good question, I look forward to seeing the answers!
Thanks for posting this!

Edit: Just read the article, she does beautiful work!

So, I did a google search on oyster shells and heavy metals, and so far I'm not liking what I'm finding...

Bioaccumulation of heavy metals in oyster (Crassostrea virginica) tissue and shell

Oysters and sediment have been collected from most major US Gulf of Mexico bays and estuaries each year since 1986. Selected samples of oyster soft tissue, shell and sediments were analyzed for Cd, Cr, Cu, Fe, Mn, Pb, and Zn for this study. Concentrations varied considerably from place to place but ratios of metals remained relatively constant. Cu and Zn are greatly enriched in oyster tissues, which is related to their physiological function. Cd is enriched in oyster shell because of the easy substitution between Cd and Ca. The concentrations of Pb and Cr in oysters are significantly lower than that in sediment, suggesting a good discrimination against these metals by oysters. Metal variations are a result of both nature and human activity.

In the article, it talks about how scientists love to study oysters because "they greatly concentrate many chemical contaminants from seawater and sediment"

Here's a thread on Backyard CHicken Keeping about heavy metals and oysters https://www.backyardchickens.com/threads/oyster-shells-and-heavy-metals.1069476/. Bonemeal, limestone,

one person tested their granite grit (not a source of calcium, just of grit)

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.

Lovely, just lovely.

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Here's (https://futurism.com/engineers-find-way-remove-heavy-metals-contaminated-water) a lovely article about how people are using oyster shells to remove heavy metals from water. These are CRUSHED oyster shells, that they added for hardness, but found the shells themselves took up copper and zinc from the water.

n Washington state, the Port of Seattle first began using crushed oyster shells — an abundant resource, given the oyster-rich waters of nearby Puget Sound — in 2005 as an additive to storm water bioretention swales at SeaTac airport. The goal was to add hardness to the runoff to reduce toxicity before the water ended up, inevitably, in Puget Sound once again. Calcium from the shells served to increase the mineral levels, but Port environmental managers also found that the runoff from outflows so treated also had copper and zinc levels reduced by about 50%.

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From Food Safety NewsSupposedly the shells growth also record the level of certain heavy metals at the time the shell was growing

On the first anniversary of the spill, the 150-year-old CAS produced a short movie highlighting the work of three of its researchers, including Roopnarine, where the narrator explained that like tree-rings, heavy metals could be detected and read in oyster shells.
...A top federal government scientist, not involved in the research, responded by saying there are now “delicate steps” that need to be taken to determine if the heavy metals in oyster shells are “dangerous or harmless” to those who might ingest them.

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So, oyster shells might be safe is harvested from clean waters...but where and how do we locate those oysters, and they're probably not for sale.

Are there downsides to bone meal or limestone for calcium?

We mostly just dry and crush the eggshells and fed them back to the chickens. Its easy enough to put the shells on the woodstove to toast nicely.  The birds prefer this to the oyster grit. Every once in a while I offer grit if the shells seem thin. They eat the shells then the grit but mostly ignore it.  They also prefer the bits of stuff they eat while free ranging. They will eat shiny metal objects too as we found a missing tiny stainless screw for a boat motor while processing a chicken.  Gave "so that's where it's been!" a whole new meaning.

I have had the same bag of grit for four years or so and it isnt even half used. They eat it so seldom I think I ill just stop using this.

Edit to add: the age of the bag may make it safer than what I could buy new as it might have less contamination than what is out there now.  Have to think about this.

We use our egg shells and feed the chooks lots of vegetables, in two years, no issues with calcium levels in our chooks.
We do have free choice bone meal out for them as well but they have not touched it much.
I am not aware of any downside to using bone meal or limestone as calcium supplements for animals.

Oysters are well known accumulators and concentrators of many minerals, that's why there is so much research published about them, they are used as indicators of ecosystem health.
They do the same job as mushrooms used for remediation cleanup of heavy metals.

Granites are going to contain the same minerals as lava rocks, granite is lava that was in a subsurface pool that then cooled slowly, in some places the granite contains uranium as well as many other heavy metals.
The concentration is what is important to know along with bio availability. This is true for most mineral additives, the key is how and what enzymes are going to process first along with the time factor.

I am really enjoying this thread by the way, lots of great information is coming out.

So it looks like what we really want is to encourage native filter feeders in any aquatic system featuring runoff, probably in the same area as the reed beds, I guess.

They would sequester excess minerals and heavy metals, and as long as the levels aren't too high, you have a local source for shellfish grit.

Should you have high levels of heavy metals, all that would be necessary is to go out and collect the shells of dead shellfish, or harvest the ones outside of the optimal breeding range, and discard the crushed shells somewhere in the system where there would be ample quantities of fungi to distribute the sequestered heavy metals in appropriate quantities and to locations where they are needed.

Personally, I think that if feeding chickens back their own shells isn't sufficient, I would increase the quantities of plant-based calcium they're being provided.

Are there any plants that contain calcium in high enough quantities that one could chop and dry it, to be fed as necessary?

-CK

Chris Kott wrote:Personally, I think that if feeding chickens back their own shells isn't sufficient, I would increase the quantities of plant-based calcium they're being provided.

I know that with my ducks, it's not sufficient. We feed them "grower," which has no calcium and supplement calcium on the side. When they're laying, they'll eat through all their egg shells and run out, so then I supplement with the oyster shell. If I don't, then we get thin-shelled or shell-less eggs. So, at least in the case of my ducks, some sort of additional calcium source is needed (I could, potentially, try to convince my family to save their egg shells from their store-bought eggs and give them to me, but I doubt they'd be game for that!)

Ours get lots of broccoli, spinach, carrot shreds, black berries, figs in season, strawberries, blue berries, lettuces, collards, kale, mustard greens.
Of their home grown foods the broccoli is the lowest in calcium at 112mg per cup and the collards are highest at 248 mg per cup.
The chooks get one large serving a day and then they are on their own foraging bugs and worms and what ever else they can find.
They get one hand full of meal worms as their before bed time snack.

We have never had an egg with a thin shell, in fact just a couple of days ago I accidently dropped one and it didn't get even a fracture line.

Dr. Redhawk, may I ask how old the birds are? I was wondering because the thin shells have been in birds in the 4 to 6 year range. The young birds with the strong shells (also dropped with no problem) have no interest whatsoever in the grit, but its the older birds that occasionally want it.  The bird herd gets to free range half a day most days, and when they dont, I try to make sure they get some greens.  Am I missing something?

I also found this article on the absorption of microplastics by scallops, a marine filter feeder.

While it doesn't talk about where the plastic is sequestered in the body, I would guess that growing a bed of filter feeders that is periodically harvested for all but the optimal breeding population and composted in the presence of oyster mushrooms might actually break down the micro- and nanoplastics, removing that problem in the same way as the heavy metals.

-CK

hau Tina, our birds are only 2 years old and they are Black Copper Marans.

Once a bird gets past "normal" laying age (4-5) they begin to age much like humans ; bone density starts going down and that has a direct correlation to their inability to fully process calcium as well as they used to.
Vitamins in their water can help the situation as well as offering them a full mineral supplement free choice (I use Sea-90 for this, 95 minerals), the mineral supplement will help the older birds process and incorporate calcium and the other nutrients they could as younger birds.
(my wife is not in love with how I tend to put the science to work for just about everything)

Redhawk

Dr. Redhawk, I will give it a try.  The older birds are Brahmas that go broody and I really don't care if they lay or not.  It's mostly that the eggs break and make a mess of all the other eggs.  The 4 year olds only have a pass due to a big predator attack because some woods near us were cut down.  Normally I rorate about the three year mark so shells havent been a problem.

Thank you for the information.

Great point. It never occurred to me bout the oyster shells but it ought to have. Doh. It did occur to me that chickens have not always had access to calcium supplements, so how did they get what they needed before oyster shells appeared magically on the farm supply store shelf? Here’s a list that came up for me in a search for calcium rich foods:

Other foods (than dairy) that are high in calcium include:
Spinach.
Kale.
Okra.
Collards.
Soybeans.
White beans.
Some fish, like sardines, salmon, perch, and rainbow trout.
Foods that are calcium-fortified, such as some orange juice, oatmeal, and breakfast cereal.

Obviously the list is intended for humans so check before giving any of these things to chickens if you’re unsure whether they’re safe for them. Nevertheless, the point is, I think, that there are loads of calcium rich foods. Chickens do like green leafy stuff. And it might be an important detail to note that in winter, when greens are scarce for many of us, chickens don’t lay eggs without our manipulationing. So if we want them to keep laying in the absence of summer greens, we’ve got to make up the deficit and maybe oyster shells don’t shake out as the best option. Microgreens, maybe? Dehydrated summer greens crumbled into their feed? Meadow hay? Dehydrated grasshoppers and other high-calcium insects? The bones left after you’ve made that delicious stock? (Maybe somewhat depleted, but the girls still go nuts for them, so there must be *something* there.)

Question... more out of curiosity than intent... would calcium carbonate (aka whiting) work? I have a LOT of that, but very finely ground for making ceramic glazes. Would it be better unfired or calcined (minimally kiln fired)? Calcined, it would be maybe a bit less dusty, but perhaps not as bio-available? Oh! Haha... I just looked it up... I never wondered before where whiting came from. Apparently whiting is basically ground chalk, limestone, marble and/or.... the sedimentation of small snails, shellfish and coral. So... full circle I guess, and we’re back to oyster shells, but in this case, ancient ones.

I mentioned this thread to the missus and she recalled that some brands of calcium supplements are made from oyster shells.  Time to check the medicine cabinet

When my husband gets rockfish, we give the carcasses to the critters.  Entertaining to watch the cat and chickens fight over them especially since Cat always loses. Last year, I had thought it seemed to help the shells, but forgot about that until this thread. Glad he has an upcoming trip and will have to be more observant for results.  

FYI - Strontium ingested at the same time as Calcium competes for absorption. That is in humans. Not sure about critters.

Am I the only one who’s not deeply concerned by this? Most heavy metals aren’t that readily absorbed through the digestive system, and we’re talking about two digestive systems, to get to me from the oyster shells. What’s more, I don’t know where in the body the chickens will tend to concentrate the heavy metals. If they just go into the shells, I guess my soil can eat the shells, and redistribute the minerals through a fungal network to plants that are rich in calcium, and my chickens can eat those. If it’s the bones, it might be a problem if I make broth, but then again, it depends on which metals and how easily they’re absorbed by my intestines.
There’s a major difference between the ingestion of heavy metals, and their injection. I do heavy metal chelation anyway, so to me this is just not scary, compared to some things.

Well this maybe explains the weird feelings I had about giving oyster shells to the chickens...not great. Honestly, I also just would prefer to reduce my reliance on purchased stuff to maintain the health of my hens. They do prefer their own egg shells crushed up over the oyster shell, no contest. They eat through them and once they run out is when they'll eat the oyster shell. I really like the idea of giving them calcium rich plants to make up the difference. Apparently, flax is super high in calcium.

I wonder if one could collect or possibly grow snails (either terrestrial or aquatic) as another source of calcium for them? Plus some extra protein. I know when I had an aquarium, the snails would get out of hand in there quite quickly. It wouldn't take much to grow some and then you could know what they'd been exposed to. Or if snails were an issue in the garden anyway, they could be collected and given to the chickens. I suppose there could be some parasite risk with terrestrial snails, but I'm guessing it's fairly low. Seems better than long term exposure to heavy metals.