Its atomic number is 82 on the periodic table.

Pb — Plumbum in Latin.

Lead is a heavy metal that is present deep within Earth’s crust. Because of its abundance, ease of extraction, and physical properties, lead has been useful to humans for millennia — in water pipes (that’s where “plumbing” comes from), solders, paints, ceramics, gasoline (tetraethyl lead), cosmetics, batteries, pesticides, bullets (lead shot), radiation shields, and other applications. Lead is also present in ores that are mined for commercial use (iron, copper, etc.), coal, and in the “flowback” during drilling operations for oil and natural gas. Lead contaminates the air, soil, and water through the mining, refining, and burning of fossil fuels, lead smelting, battery manufacturing and disposal, and by waste incinerators. Soil can be contaminated from present-day industrial emissions and gasoline fumes from decades back. (What goes up as air pollution eventually comes down and lands in surface water and soil — if it doesn’t end up in our lungs first.)

What lead is, how we used it in the past, how we will use it in the future, and how people are exposed to contamination in the environment are not trivial matters because lead is toxic to humans in small amounts. And no one is more vulnerable to those toxic effects than children.

The scientific and medical communities have known for decades just how toxic lead is, especially to the developing brains of children. Research performed at the University of Pittsburgh in the 1970s and 1980s by pediatrician Herbert Needleman and others sounded the alarm regarding the dangers of lead exposure in children and sparked the U.S. government to ban the use of lead in many consumer products, especially gasoline (where tetraethyl lead was added to improve automobile engines’ performance) and paint. But decades before Dr. Needleman’s research finally made an impression upon the public’s mind, health concerns about lead exposure that were voiced by knowledgable and articulate scientists were ridiculed, discounted, or ignored by people who should have known better. (This is an old theme — progress vs. precaution, polluter vs. environmental protector — that continues to play out today in national conversations about environmental degradation, climate change, and public health.)

Exposure to lead in children and adults occurs in the lungs, where lead molecules piggybacking on particulate matter (dust) enter the tiniest airways and are readily absorbed into the bloodstream. More commonly, as we will see in the next few days, exposure occurs in the gastrointestinal tract after lead-contaminated paints, water, and food are ingested and absorbed. Children are especially prone to lead poisoning because they like to play in dirt that, unbeknownst to them, may be contaminated with lead. They are also less inclined to wash their hands before putting their fingers, toys, debris (ie. paint chips), and food in their mouths. For those reasons — and because children breathe more air and drink more water per unit volume compared to adults — they are at highest risk of exposure to lead and other environmental toxics.

Tomorrow, we’ll see what exposure to lead looks like in a developing brain.