Atomic bombs, leaded gasoline, Teflon: DuPont Co. built materials that powered the products defining American industrial and military might in the 20th century.

Jobs have been scaled way back at old DuPont sites along the Delaware, Ohio, and other great rivers. But the plants remain home to caustic and cancer-causing byproducts, held back by pumps, pipes, and barriers, not to mention litigation and negotiations with local governments, community groups, and regulators.

Who's going to manage these long-term threats, now that DuPont is spinning off old chemical units into a smaller new company, Chemours, on July 1?

"DuPont and Chemours remain committed to continuing to fulfill all of their environmental and legal obligations in accordance with existing local, state, and federal regulatory guidelines," company spokesman Daniel A. Turner told me.

In fact, Chemours is taking over many cleanup responsibilities from its parent company for an "indefinite" period, according to documents it has recently filed with the Securities and Exchange Commission. The "ultimate costs are difficult to accurately predict," Chemours added. Its long-term obligations are "uncapped."

Chemours accounts for $7 billion of DuPont's $35 billion in yearly sales.

The spinoff may end up owing billions more than it can pay, without DuPont's deeper pockets, Maggie Flanigan, spokeswoman for Parkersburg, W.Va.-based Keep Your Promises DuPont, a community activist group, told me.

Chemours says it faces 2,400 asbestos-related lawsuits from ex-DuPont contractors, and 3,500 Ohio and West Virginia lawsuits alleging injury or disease from perfluorooctanoic acids (PFOAs) formerly used to make Teflon, Gore-Tex, and other useful polymers.

PFOAs, a DuPont-backed doctors' panel found, have been linked to pregnancy problems, kidney and testicular cancers, thyroid disease, and high cholesterol. DuPont has pledged up to $235 million to monitor 80,000 customers of West Virginia utilities for PFOA-related problems. That work is proceeding slowly, according to the company's own account.

Chemours has also identified $274 million in estimated pollution-control expenses under the federal Superfund program at some of the DuPont sites it is taking over. That includes lead and mercury cleanup in Pompton Lakes, N.J.

Closer to headquarters, the EPA says DuPont's 123-year-old, 1,455-acre Chambers Works complex, in Deepwater, Salem County, which New Jersey officials are touting as a future Chemours headquarters site, is contaminated with toxic polychlorinated biphenyls (PCBs), radioactive materials, and heavy chemicals.

A 40-year-old pumping system sends 1.5 million gallons a day through a DuPont wastewater treatment plant at Deepwater; the treated water goes in the river. Volatile organic chemicals and PFOAs flow underground; EPA, Chemours, the Army Corps of Engineers and the New Jersey Department of Environmental Protection are investigating what else to do and how much it will cost. There are similar issues with benzene and PCBs at DuPont's 1,900-acre Repauno site in nearby Gibbstown, which remains part of DuPont.Federal agencies are investigating what needs to be done at the 1,445-acre site.

At the Chemours Edge Moor titanium-dioxide plant, north of Wilmington, a Risk Analysis Report "is currently being drafted," according to an EPA report.

Last Tuesday, the Parkersburg-based activists sent a letter to the SEC

asking the agency to review whether the Chemours

spinoff was likely to make it harder to pay for future damages linked to the old DuPont plants.

The SEC didn't write back, according to Flanigan. The agency approved the spinoff Thursday.

215-854-5194@PhillyJoeD