Which element has created unsafe levels in the blood of 500,000 children one to five years old, according to the cdc?

The correct answer is- lead level in blood.

Explanation:

In USA there is 1.2 million children have high lead level in blood. According to the CDC in which 0.5 million children have found unsafe level of lead in the blood.

If a child has 5mcg/dl he is consider to have high level of lead blood level and 45 mcg/dl level is unsafe or danger level of the lead blood level and need to decrease it immediately.

Thus, the correct answer is - lead level in blood.