Since our environment contains lead, every natural source of calcium will contain some lead. The key is to minimize exposure by selecting higher quality sources. Since coastal waters are often highly polluted due to rain runoff and river outflow, oyster-shell calcium may contain prohibitively high levels of lead and other contaminants. Bone meal from older animals would also likely contain higher amounts of lead. Stringent testing of raw materials ensures a calcium supplement that meets established quality standards. A reputable company will be able to supply these assays upon request.