Perfluorooctanoic Acid, commonly known as C8 for its chemical formula (C₈HF₁₅O₂), is a manmade chemical used by E. I. du Pont de Nemours and Co. from 1951 through 2012 to produce Teflon at its Washington Works plant located on the Ohio River near Parkersburg.

Medical experts have linked C8 exposure to health problems in humans, including kidney and testicular cancer, thyroid disease, low birth weight, high cholesterol and chronic obstructive pulmonary disease. It builds up and persists in the blood, and it is known to be toxic and carcinogenic in animals. C8 has a "suggestive" risk for cancer, according to the Environmental Protection Agency.

Studies later determined that C8 concentrations were found at least 413 miles downstream. Alleging health problems related to C8, thousands of residents in the Parkersburg area brought suit against DuPont. Their lawsuits charged that DuPont knew the health risks that were posed by C8, but instead of taking steps to reduce the risks the company increased its use.

A 2004 class-action settlement required DuPont to offer to pay the costs of medical monitoring for nearly 100,000 people in the area. Subsequently, fewer than 7,000 residents registered for the monitoring. More than 3,500 residents opted out of the class-action settlement to instead pursue individual lawsuits.

In 2015, DuPont formed the Chemours Company, a spin-off business that began operating DuPont's Washington Works plant. When six so-called bellwether C8 suits went to trial, defense lawyers representing the two chemical companies argued that DuPont had reacted to the C8 issue using the best science of the time and spent $594 million to address the problem. Attorneys for the plaintiffs argued that DuPont had known since 1980 that C8 causes cancer in rats and attempted to cover up the fact that C8 was a toxic danger to humans and the environment.

Of the six suits, DuPont and Chemours lost two and settled the other four. The purpose of these bellwether suits was to provide guidance in addressing the other suits, and in February 2017 the two companies agreed to settle the thousands of remaining suits, paying the plaintiffs a total of nearly $671 million. News reports indicated that 200 plaintiffs with cancer were expected to receive at least $1 million each. At the lower end, those with high cholesterol were expected to receive awards in the five figures.

On February 7, 2018, Ohio Attorney General Mike DeWine filed a lawsuit against DuPont and Chemours, seeking reimbursement for Ohio's costs of investigating and cleaning up C8 contamination in the Ohio River. The Ohio lawsuit seeks the following: A declaration of DuPont's duty to compensate Ohio for expenses related to the contamination; damages for injury to Ohio's natural resources, including the economic impact to the state and its residents; an award of present and future costs to clean up C8 contamination; and restitution damages for profits DuPont obtained through the conduct.

"We believe DuPont should pay for any damage it caused, and we're taking this action to protect Ohio, its citizens and its natural resources," DeWine said.

On November 22, 2019, the film Dark Waters, a legal thriller based on the C8 controversy and starring Mark Ruffalo and Anne Hathaway, was released to positive reviews. In 2022, the U.S. Environmental Protection Agency (EPA) issued new advisories that significantly lowered the allowable amount of C8 in drinking water. In 2023, Chemours announced it would conduct additional testing for "forever chemicals" in water samples near the Washington Works facility.