Lead is a uniquely cumulative poison. Some of the kinds of neurological damage caused by lead are not reversible. The period from 1 to 3 years of age in humans is critical for lead exposure, and neural damage occuring during this period is least likely to be reversible. Most important, children excrete lead very slowly. Lead behaves chemically very much like Calcium, and is similarly stored in bone.
Bone is in a dynamic equilibrium, biologically and chemically, with blood.
If the rate of lead intake is reduced, lead will enter blood from bone. During periods of high calcium demand, as in lactation and pregnancy, lead enters the blood along with the calcium. In older people, when bone mass is reduced by resorption, higher lead levels have been observed. This is especially true of post-menopausal women, who are greater risk of osteoporosis. It is also important to be aware that the lead available from the tested products would not be the only source of exposure in a child's environment.