'I've heard claims it can carry heavy metals': We use Natural Clinoptilolite Zeolite, which is the one used for human consumption. Mines that harvest it purify it to render it free of toxins so that it can magnetize positively charged molecules in your body. Additionally, the mine we get our zeolite from goes an extra step and handles ours differently to ensure it is not tainted even with diesel fuel fumes. Nevertheless, there are many studies done on natural zeolite safety and efficacy and not one shows toxicity if using standard parameters.