Lead

The soft, heavy metal that humanity wove into daily life across six millennia — in Roman water pipes, pewter, paint, solder, and gasoline — before reckoning with the fact that it is a cumulative brain poison with no safe dose, especially for children, and that the slow acknowledgment of that fact cost generations their cognitive potential.

For most of human history, lead was considered one of nature's great gifts. It melted easily, resisted rot, shaped without complaint, and lasted for centuries. The Romans lined their water pipes with it and flavored their wine with it. In the twentieth century, engineers added it to gasoline to stop engine knock. It went into paint, plumbing, ceramics, and solder. Only gradually did the evidence accumulate that this indispensable metal was poisoning the people who used it — and that the harm, concentrated in children's developing brains, had been happening for a very long time.