The human body needs a diet enriched with many ingredients from the periodic table that sound less like food than like machine parts or spare change. We must have iron to capture oxygen, copper and chromium to absorb energy, cobalt to sheathe our nerves and zinc to help finger our genes. Other creatures demand the occasional sprinkling of tin, nickel, platinum, tungsten and even strontium.

But when it comes to lead, the 82nd item on Mendeleev’s menu of the elements, the universal minimum daily requirement is zero. As far as we know, neither we nor any known life form needs the slightest amount of lead to survive. And for humans, especially infants and young children, consumption of even moderate amounts of the metal can have serious consequences.

Developing brains seem to be extremely sensitive to the effects of the metal, which is why many scientists who study lead were distraught by the latest news of lead paint’s being used on children’s toys.

“I’m not normally a rabble rouser, but I’m disturbed by the potential enormity of this problem,” said Jeremy R. Knowles, a professor of chemistry and biochemistry at Harvard. “We’re talking about millions of toys, and the possibility of an entire generation of children being exposed to gratuitous constraints on their neurological development.”