The blood lead levels used to indicate harm potential status and trends in public health can be very misleading, since they primarily only indicate current lead exposures or uptake only during the last several months. Blood lead levels quickly reduce by the body sequestering the lead in bones and teeth in accumulative fashion. This sequestration does help the current toxic risk of other physiologic pathway degradation, but tends to only put off the risks until stresses later in life (old age, illness, or pregnancy) develop to cause the body to seek to mobilize the calcium stores in bone to fill the sudden need for added calcium to build defensive molecules needed to counter the stresses. At such times, calcium is low in supply, and since the body does not correctly identify lead as being other than calcium, lead comes out with the Ca and becomes incorporated into the defensive components being made from calcium and zinc. This contamination of stored lead makes many of the molecules such as zinc finger proteins dysfunctional. The body thinks that it has responded well to the stress but has not because the accumulated body lead has poisoned the bodies’ defenses. Blood lead levels can thus drop well, because either the exposures have lessened, or because the body has been effective in storing it in bone, or both mechanisms. Any time the bbl drops, helps the current pathogenicity of the lead to the immediate physiology, but usually only postpones the damage till later in life when stresses remobilize it at precisely the vulnerable times of old age, illness, or pregnancy. Once body burden has increased, we all have increased risks through life from that lead uptake that has occurred earlier. The public health paradigm commonly misrepresents the meaning of the blood lead testing results, erroneously giving the impression that the dangers from the lead exposures have all passed, but science is not served well by this incomplete picture provided by the authorities. Bone lead levels are now 100 to 1000 times those that prehistoric bones had accumulated. Our bodies have not had evolutionary time elapsed to adapt better defense mechanisms to the greatly increased environmental pollution once we dug the lead up out of the ground and dispersed it around the globe as products that easily degrade to be taken up to contribute to our health challenges. As you say, prevention is primary, because once in the body, much of it stays there to eventually do more damage.