According to the Centers for Disease Control and Prevention:
No safe blood lead level has been identified. For infants and young children, lead levels of 10 micrograms or more in a deciliter of blood can damage ability to learn. (A microgram is one millionth of a gram. A deciliter is about half a cup of liquid.)The toxicity of lead has been recognized since at least the late 1700s.
Of all people, young children face the most danger from exposure to lead because their growing bodies absorb lead more easily than do adults' bodies. Pregnant women and women of childbearing age should avoid exposure to lead because lead ingested by a mother can affect the unborn child.
At higher blood lead levels (that is levels equal to or greater than 25 micrograms per deciliter), lead can damage people's kidneys, blood, and nervous system. At very high levels, lead poisoning can cause mental retardation, coma, convulsions, or death. (Spotlight on Lead. CDC’s Third National Report on Human Exposure to Environmental Chemicals.)
Today, there are efficacious evidence-based treatments for accidental exposure to lead and strong regulation of the element’s use. People concerned with the effects of lead exposure should be working to further reduce lead use in manufacturing and consumer products. Further experimental demonstration of the deleterious effects of lead is unwarranted and wantonly cruel.
In spite of these simple facts and obvious conclusions, primate vivisectors continue to demonstrate that lead exposure is harmful to monkeys, and especially so when the exposure occurs at a young age. See:
Wu J, Basha MR, Brock B, Cox DP, Cardozo-Pelaez F, McPherson CA, Harry J, Rice DC, Maloney B, Chen D, Lahiri DK, Zawia NH. Alzheimer's disease (AD)-like pathology in aged monkeys after infantile exposure to environmental metal lead (Pb): evidence for a developmental origin and environmental link for AD. J Neurosci. 2008.
Schneider ML, Moore CF, Gajewski LL, Laughlin NK, Larson JA, Gay CL, Roberts AD, Converse AK, DeJesus OT. Sensory processing disorders in a nonhuman primate model: evidence for occupational therapy practice. Am J Occup Ther. 2007.
Lasky RE, Luck ML, Parikh NA, Laughlin NK. The effects of early lead exposure on the brains of adult rhesus monkeys: a volumetric MRI study. Toxicol Sci. 2005.