Approximately what percentage of lead is stored in bone?

• A. Blood 5-10%
• B. 5-10%
• C. 20-30%
• D. Bones 80-90%

Answer: (D)

Lead tends to become part of bone minerals, substituting for calcium in the bone matrix. Because of that, the skeleton acts as the body’s main long-term storage site for lead. In adults, roughly 80–90% of the total body lead is stored in bone, with the remainder in soft tissues and a small, fluctuating amount in the blood that reflects recent exposure. Blood lead levels mainly indicate recent exposure, since only a fraction of total lead is circulating at any moment. The bone reservoir turns over slowly but can release lead back into the bloodstream when bone turnover increases (such as during pregnancy, lactation, or aging). This is why bone stores dominate the body’s lead burden. So, the approximate percentage stored in bone is about 80–90%.