It is a known fact that because of Bentonites’ volcanic origins, they will have small trace amounts of metal oxide trace elements, primarily aluminum but also lead, mercury and even arsenic. On the average, clays contain 70-90 trace minerals in parts per million (ppm). These heavy metal trace minerals in Bentonite clays are safe because they are not bioavailable to the body. They serve another purpose.
Bentonite Clay Info Blog 