(Bloomberg) -- DuPont de Nemours Inc. and its 2015 spinoff Chemours Co. have agreed to a $4 billion settlement of a dispute over environmental liabilities that were shifted to the new company.The accord, which also includes DuPont’s former seed business Corteva Inc., covers payments for liabilities tied to a class of chemicals known as PFAS, the companies said in a statement on Friday. DuPont and Corteva will split “certain qualified expenses” 50-50 with Chemours, the companies said. They specified expenses incurred over a term of 20 years or $4 billion at most.

PFAS are widespread in the environment and human blood after decades of use to make things slippery, nonstick or waterproof. Their bonds are so stable that they’re known as “forever chemicals.” Used to make items like carpets, fabrics and firefighting foams, they’ve been found at high levels in some areas, particularly around airports and Air Force bases, prompting concerns about drinking water and creating costs for municipal water systems and states.

Studies have linked them to diseases like cancer, immune harm and other ills. Their dangers were the subject of the 2019 movie “Dark Waters,” featuring Mark Ruffalo as a crusading lawyer.

‘Unlimited’ Liabilities

The companies also agreed to pay $83 million to resolve almost 100 cases covered by multidistrict litigation in Ohio. DuPont and Corteva each will contribute $27 million, while Chemours will pay $29 million.

QuickTake: Why Action on ‘Forever Chemicals’ Is Taking So Long

The chemicals had been a concern for DuPont even before it spun off Chemours, the division that made them. At the time, it had estimated that cleanup costs would be $295 million to $945 million, and had already stopped making some versions of the chemicals, which are an entire class of compounds numbering in the thousands.

Chemours sued DuPont in 2019, arguing it hadn’t signed up to cover “unlimited” liabilities racked up by DuPont and that its former parent’s estimates on what it would shift to Chemours were “spectacularly wrong.” A judge ruled last year that Chemours must arbitrate its dispute with DuPont. The companies said the settlement resolves the ongoing arbitration.

The case is Chemours Co. v. DowDupont Inc., 2019-0531, Delaware Chancery Court (Wilmington).

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