I dont know of much that doesn't cause cancer in the state of Cali, LOL...seriously though, I don't know. There are many alternatives to buffer your water and add calcium for your snails. You can add calcium pills to the tank, or tums, for them to graze on. Crushed coral can be used as a substrate or in your filter to buffer the water and increase pH to prevent erosion. Foods are always a great option to promote healthy shell growth. These plaster discs are just one inexpensive option, if you are at all uncomfortable about it, I wouldn't do it. Just use one of the other options.