PORTLAND, Maine (AP) — The biggest water district in Maine is suing manufacturers of so-called forever chemicals in the hopes of recouping costs of monitoring and treating polluted wastewater.

The Portland Water District lawsuit comes as the cost of the disposal of PFAS-contaminated sewage sludge has doubled from $1.6 million to $3.2 million over the last three years, and Portland has agreed to develop a regional biosolids treatment facility proposal with cost estimates ranging from $150 million to $250 million.

The lawsuit, filed last month in U.S. District Court in South Carolina, targets 18 companies including DuPont, 3M and others that designed, manufactured, marketed, distributed and sold six toxic forever chemicals.

“Defendants knew or reasonably should have known that their PFAS compounds would pollute wastewater treatment systems and threaten public health and welfare,” the lawsuit said.

In a statement, 3M said it will address PFAS litigation by defending itself in court or through negotiated resolutions. “As the science and technology of PFAS, societal and regulatory expectations, and our expectations of ourselves, have evolved,” the company said Wednesday.

A spokesperson for DuPont said the company that emerged from a corporate split in 2019 has never produced PFOA or firefighting foam. “While we don’t comment on pending litigation matters, we believe this complaint is without merit, and we look forward to vigorously defending our record of safety, health and environmental stewardship,” the company said.

PFAS is short for per- and polyfluoroalkyl substances, which are chemicals that can accumulate and persist in the human body for long periods. Evidence indicates that exposure to the chemicals may lead to cancer or other health problems,

The Portland Water District lawsuit focuses on wastewater. The district is already in compliance with strict EPA limits on certain PFAS in drinking water that will require utilities to reduce them to the lowest level they can be reliably measured.