NOT TOO LONG AGO, as a graduate student, I took a crash course in lead. I moved to Vermont from the Midwest to study the geochemistry of lead in soil, and because I needed samples for my project, my professor and I decided to test a 100-year-old house his family had bought. Houses of that age are poisonous onions; peel back the outer layers and you are likely to find leaded paint, which the federal government didn't ban for residential use until 1978. Decades of wind and rain had scattered paint chips around the outside of the house. We twisted augers into the ground and came up with ten bags of soil while his wife painted the living room and his 6-year-old son played in his bedroom.

Back in the lab, I ground up a few tablespoons from a sample and analyzed the powder with an X-ray gun. The lead concentration was more than 25 times the limit the Environmental Protection Agency deems hazardous in soil. The proportion of lead-to-soil was near the proportion of chili powder in a good chili.

It was a scary reminder that despite all the protective behaviors we might knowingly adopt -- be mindful when renovating an old home; wear a respirator at the firing range -- lead is invisible and all around us. I was stunned to learn that lead arsenate, a pesticide that was applied for nearly a hundred years in American apple orchards, was likely contaminating soil in abandoned farm fields where I hoped to find tasty morels. Preliminary data suggest that the mushrooms sometimes absorb soil lead at levels that exceed the Food and Drug Administration's limit for safe consumption.

Unfortunately, the last presidential administration missed an opportunity to meaningfully strengthen the out-of-date standards for contaminants like lead, and even loosened some restrictions. This is despite a steady stream of science linking lead to terrible health outcomes, especially for children, and gut-wrenching news items identifying more and more exposure pathways, such as the recent report of a House oversight subcommittee that found elevated lead in many common baby foods (even in some organic brands). 

While some petroleum-based contaminants decay over time, lead does not biodegrade to become less harmful, meaning it tends to stay in place. Despite our best intentions, removing lead-contaminated soil around each lead-painted home in the U.S. would involve landfilling valuable soil, costing nearly $10,000 per home. With 38 million homes estimated to harbor lead-based paint as of 2002 -- a figure that is likely lower today, due to demolitions -- getting rid of all lead-contaminated soil around houses would be an impossible task. And landfilling lead-contaminated soil doesn't really end the problem. It just shifts the burden to a different area within range of a hazardous waste dump. Removing the topsoil where lead tends to accumulate also displaces a highly biodiverse part of the soil ecosystem. Although it gradually sinks deeper into the soil over time, if it doesn't hitch a ride on a SpaceX rocket, lead is here to stay.

The most sustainable clean-up solutions for lead-contaminated soil involve simply planting shrubbery, so the soil is less likely to move -- or be eaten by a two-year-old. Another alternative is to manipulate the behavior of the element by adding phosphate, which binds tightly to lead and makes it less likely to be absorbed by humans and other organisms.