Lead toxicity

Tha main exposure of lead is through the respiratory and gastrointestinal track.
when adsorbed, the 99% of the lead will be bound to erythrocytes for about a month.
thus dispersing the lead over the body.

Lead will interfere with enzymes and structural proteins. Most prominently
affecting the heme synthetic pathway, specifically the enzyme delta-aminolevulinic acid dehydratase (delta-ALAD; ALAD) the interference of heme production and drop in heme body pool is one of the main reasons of lead related pathology. When blood lead levels exceed 20 ug/dL, ALAD is inhibited by 50%. this prevents aminolevulinic acid (ALA) From converting to porphobilinogen, preventing iron from being incorporated to the protoporphyrin ring (holds iron).Thus there is a reduction of hemoglobin and cellular respiration.

http://www.altmedrev.com/publications/11/1/2.pdf