Dan Richter speaks plainly. “Sad to say, soils in cities have been scientifically neglected,” he says. Soil scientists have historically worked to improve agriculture – “after all, we need to eat!” But the soils most of us walk around on daily, whose dust we kick up and absorb through our skin and breathe in? That’s mostly been an empty spot on the data chart.
Richter, Theodore S. Coile Distinguished Professor in the Nicholas School of the Environment, is working to change that. He has spent much of his career focused on the soil of forests and fields, but in 2018, a graduate student had interest in soil contamination, and so they began testing all over Durham. “City soil mapping writ large,” he says – testing soil along roadsides, along house foundations. A Bass Connections project in the next years yielded not just information about Durham soils but the first city map of lead levels in soil in North Carolina.
Meanwhile, hanging in his lab was a 1937 Bureau of Public Works map of Durham, showing not only Durham’s streets but community buildings, parks, schools and infrastructure like incinerators. Richter recognized the location of one of those incinerators. “I’m a 40-year Durham citizen,” Richter says. “I said, ‘That’s Walltown Park!’” A minute on Google Maps and he and his students had identified four parks built on incinerator sites. “It was an instant project.”
He and students took a portable X-ray fluorescence (XRF) analyzer and started testing, yielding results that showed that several Durham parks were contaminated with lead leftover from the incinerator ash. Where most environmental lead comes from residue of lead paints and the lead that used to be in gasoline, this was a different problem.
“Fires concentrate metals,” Richter says. Combustible materials leave, but metals like lead build up in the ash, and that ash had been used as soil amendments in building the parks and elsewhere. The readings and samples showed hot spots – some above EPA safety thresholds – in the parks, some of which have closed. Richter has been drawn sufficiently into Durham politics that he plans to spend two days a week in an upcoming sabbatical learning about remediation.
But research always leads to more research. “My lab came out of the experience of finding 80-year-old lead contamination in city parks in Durham and asking the question, ‘This isn’t just a Durham story, is it?’ It’s probably a much bigger story.” They have been researching forgotten incinerators all over North America and the contemporary use of that land. He hopes machine learning can make such research easier and faster in the future: “Where were all the gas stations in Durham through time? OK, that’s a nice data set. Probably somebody should go out there with an XRF and in 20 seconds, zap the ground a few times.” The XRFs have GPS connections, so he envisions instant data mapping.
More, a colleague in California, aware of the city soil-mapping project, reached out about soil left after the 2025 Southern California wildfires. “I sketched them out a sampling protocol,” he says. “By two weeks later my house mailbox would have piles of boxes from citizens sending me samples.” The Duke Soils Lab is right where Richter hoped it would be: “Trying to locate city-soil contaminant hot spots and creating a new city-soil science.”