Across Appalachia and the Rust Belt region, including throughout the city of Pittsburgh, former industrial sites are being transformed into new neighborhoods, research centers and technology hubs.

But another transformation has been taking place beneath them for decades.

Brownfields are former industrial or commercial sites. Redevelopment there can be complicated by pollution. They’re often defined by what was left behind: abandoned factories, vacant land, and soil contaminated with carcinogenic compounds.

But beneath the surface, brownfields remain living ecosystems. Billions of microbes inhabit these soils. In Pittsburgh, some have spent decades responding and adapting to the pollution of the city’s industrial past.

I am a microbiologist who became interested in this topic through a brownfield practically in my own backyard. My lab at Carnegie Mellon University is just 2 miles from Hazelwood Green, a 178-acre former industrial site at Pittsburgh’s riverfront along the Monongahela River.

For more than a century, this area was home to steelmaking operations, including the Jones & Laughlin Steel Co.. At its peak, the site employed thousands of workers and helped earn Pittsburgh its reputation as the Steel City.

Pittsburgh’s industrial history also left a chemical legacy. Like many former industrial sites, Hazelwood Green contained soil contaminated with petroleum hydrocarbons, heavy metals and other pollutants, resulting in its classification as a brownfield. Among these contaminants are benzene, toluene, ethylbenzene and xylene, a group of petroleum-derived compounds collectively known as BTEX. These chemicals can be toxic to humans and other organisms, and some are known carcinogens.

Over the past several decades, substantial effort has gone into redeveloping Hazelwood Green. The remediated Hazelwood Green site is now a new center for research,........

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