Scientific American has published a good article outlining why lead remains a danger years after it was banned from paint and gasoline: Lead Exposure on the Rise Despite Decline in Poisoning Cases.
Lead poisoning is caused by acute exposure at high concentrations, like when a child eats paint chips. But “even though the average concentration of lead in the American bloodstream has dropped by a factor of 10 since the late 1970s, the levels are still two orders of magnitude higher than natural human levels, which have been determined by studying skeletal remains of native Americans dating to before the industrial revolution.”
Recent data demonstrates that health complications from lead arise even at low exposures, prompting scientists to advise the EPA and health departments to lower the concentration deemed acceptable in the bloodstream. [...]