Pittsburgh’s soil is contaminated in some areas by five toxic metals emitted by historic coking and smelting from the region’s now-diminished coal and steel industry, according to a new study by geologists at the University of Pittsburgh.

In a city with a history of air pollution so bad that a 19th-century writer for The Atlantic magazine called it “hell with the lid taken off,” the study shines a light on the legacy of more than a century of steel making in western Pennsylvania.

It found arsenic, cadmium, copper, lead and zinc in soils, especially in the eastern half of Pittsburgh, where the contaminants had likely been blown by prevailing winds, and trapped by the city’s temperature inversions which keep pollution close to the ground beneath an upper layer of warm air.

“Along with worsening air pollution…inversions may have given heavy metals from historic industrial sites a chance to settle from the air into the soil,” the university said in a press release this week.

Scientists from Carnegie Mellon University and the Allegheny County Conservation District collected samples from 56 sites, including parks and cemeteries that were away from other contamination sources such as roads, roofs or gutters. Their findings were correlated by University of Pittsburgh researchers to sources of industrial pollution, and published in July by the journal Environmental Research Communications.

The paper is believed to be the first anywhere to examine the legacy of decades of industrial pollution on soils, the authors said.

“This is the first study we know of that samples/measures background soils, maps them, and then uses source signatures to understand background patterns in soil chemistry,” they wrote in an email.

Although the study focused on legacy pollution, it’s likely that steel-industry plants such as U.S. Steel’s Clairton Coke Works south of Pittsburgh are still contaminating soil, said Alexandra Maxim, a former Pitt graduate and now a Ph.D. candidate at Georgia Tech who led the study,  and her co-author, Daniel Bain, an associate professor at the University of Pittsburgh.

“Our data cannot implicate any of the remnants of the steel industry, but the patterns we observe suggest areas around coking facilities were receiving contamination that looks like coking emissions. So modern contamination from industries operating like those responsible for the observed contamination seems likely,” they said in the email.

Still, the study did not identify any harms to human health or the natural environment. Maxim said there are too many variables, such as whether soil gets in the human mouth or whether the digestive system can separate the toxic metal, to draw any conclusions about whether the metals have negative health effects.

“This is more of a first step, where we evaluate how bad the contamination is, particularly in areas that aren’t necessarily measured that often,” she said.

Amanda Malkowski, a spokeswoman for Pittsburgh-based U.S. Steel, which has long dominated the industry in the region and still operates three plants there, said the company “follows local, state and national rules and guidelines that are in place for our operations.”

Although most of the contaminants were found below levels that trigger action by regulators, they may warrant soil testing by residents who grow vegetables or allow their children to play in places where they may come into contact with the soil, said Maxim. 

“I don’t think people need to be scared but I think they need to be aware,” she said in a statement. “Make sure you test your soil, and be thoughtful about your gardening and your children playing in certain areas.”

Other precautionary measures include using raised beds for gardening or laying down paving stones for children to play on, Maxim said.

The only metal that exceeded a standard set by Pennsylvania’s Department of Environmental Protection was arsenic, which was found at a median reading of 13.9 milligrams per kilogram, above the DEP’s soil “action level” of 12 mg/kg. The median occurrence for lead was 99 mg/kg, well inside the official limit, while copper, zinc and cadmium were also significantly lower than the state level that requires cleanup.

Lead in soil seemed to be “strongly influenced” by secondary smelting, the study said, but it acknowledged that the metal’s previous status as a gasoline additive may account for the lead found in soil.

“Care was taken to ensure near-road environments were not sampled, avoiding hotspots of lead contamination, but we cannot rule out the potential that this historically dominant source impacted broader areas,” it said.

The peer-reviewed paper, titled “Urban soils in a historically industrial city: patterns of trace metals in Pittsburgh, Pennsylvania,” noted that a concentration of steelmaking and other industries along the Allegheny and Monongahela Rivers likely contributed “a mix of various metals to Pittsburgh soils.”

It argued that its findings have implications for cities around the world, especially now that developments such as urban gardening and green infrastructure have the potential to disturb soil contamination, and increase exposure for humans and natural systems.

There were a wide variety of contamination sources in Pittsburgh so it’s challenging to attribute metals in the soil to specific sources, the paper said. But it identified five chemistry sources that are linked to metals in the soil: fly ash from coking; the bulk chemistry of coal; bedrock; fly ash from coal-fired power generation, and secondary lead smelting.

Together with the effects of frequent temperature inversions in the river valleys where industry was concentrated, and the prevailing winds, the industrial outputs are likely to have affected the land as well as the air, the paper said.

“This concentration of atmospheric pollutants for extended periods of time has the potential to focus and encourage deposition of this contamination on the land surface,“ it said.

The study, which collected samples in 2016 and analyzed them through 2019, was funded by the Heinz Endowments, the Henry Leighton Research Fund at the University of Pittsburgh and the National Science Foundation.