A US court has begun hearing the first of several cases in what began as a class action suit against DuPont, in which plaintiffs claim the US chemical giant was to blame for their illnesses. The company has denied all allegations.

All of the estimated 3,500 cases center around discharges of perfluorooctanoic acid (PFOA or C8) from the chemical producer’s Washington Works plant in Parkersburg, West Virginia. The case that opened on Sept. 13 was brought by an Ohio woman, Carla Marie Bartlett, who charges that the chemical found its way into drinking water supplies and caused her kidney cancer.

The Bartlett case is being regarded as an early test of potential liability for the discharges alleged to have persisted for several decades. A second trial is due to start Nov. 30.

While DuPont is named as the defendant in all of the cases, some of the liability has been inherited by Chemours, the July 2015 spin-off of the company’s Performance Chemicals business segment.

The lawsuits charge that DuPont, which claims to have since phased out the potentially toxic chemical in manufacturing its Teflon-brand fluoropolymer, continued to use it for decades even after learning that it had been discovered in nearby drinking water supplies in the states of Ohio and West Virginia.

In 2001, affected residents brought the original class action suit against DuPont over C8 exposure. According to US media reports, the company settled in 2004, agreeing to fund medical monitoring programs and install new water treatment systems. It also agreed to convene a panel of scientists to determine whether any diseases were linked to C8.

After a more than seven-year study, the panel concluded there was a probable link between C-8 and six diseases – kidney and testicular cancer, ulcerative colitis, thyroid disease, pregnancy-induced hypertension and high cholesterol – leading Class members with one of those diseases to individually sue the company.

Although DuPont agreed to forego challenge as to whether C8 can cause those diseases, the plaintiffs nevertheless must prove that the chemical is directly to blame. In the current case, the company is on record as saying it believes Bartlett's exposure was insufficient to cause health problems and that other factors, such as obesity, may be to blame for her cancer.

In 2005, DuPont paid $16.5 million to the US Environmental Protection Agency (EPA) to settle allegations it hid information on health risks associated with C8.