We got on the subject of calcium supplementation and they very strongly advised me not to give oyster shell because it was ground from some washed up shells and full of mercury and other toxins
Not really "full of".
My take on this is that it's far more likely to be a legitimate health issue for a person consuming calcium supplements daily for forty years than for a chicken that lives for, well, however long your personal chickens live
And it is not like chickens aren't exposed to other sources of heavy metals too, well beyond what's considered acceptible for humans... heck, we use galvanized waterers
she uses mashed up Tums to supplement the calcium.
Sure, if she can afford it and is okay with the *other* ingredients in Tums (Sucrose, Calcium Carbonate, Corn Starch, Talc, Mineral Oil, Natural & Artificial Flavors, Adipic Acid, Sodium Polyphosphate, Red 40 Lake, Yellow 6 Lake, FD&C Yellow 5 Lake (Tartrazine), Blue 1 Lake), then why not.
OTOH to *me* anyhow there is not a persuasive case not to use oystershell for chickens. Dry and crush their eggshells and feed 'em back to the chickens if you are concerned... that way you will use only a minimum of oystershell and will therefore have minimal inputs of whatever contaminants you are concerned about.
Me, I'd feed oystershell and eggshells, and if I felt guilty about it I'd take the money I saved by not feeding Tums and give it to the charity of my choice
I am an artist and have ceramic supplies on hand and I have a bag full of straight up Calcium Carbonate
Actually I'd be
more worried about using that than using the oystershells, since at least we have some idea what the general level of contamination is in oystershell
No source of calcium carbonate (well, no cheap source) is going to be COMPLETELY pure, and many sources have a considerable amount of lead and other heavy metals, moreso than oystershell has. Personally I wouldn't do it.
Basically there's no such thing as a free lunch -- pretty much everything has *some* contaminants or production aspects to object to
Not all levels of Stuff are necessarily a realistic health threat.
JMO,
Pat