Creating a massive lawsuit over cancer-linked chemicals found in around a third of Americans’ drinking water got a skeptical reception in federal court Thursday.

A panel of seven judges in Manhattan repeatedly asked whether cases across the U.S. should be consolidated, given that they may have dealt with different “delivery mechanisms,” or ways the chemicals got into water. The court heard arguments from more than 20 lawyers over whether to consolidate more than 70 lawsuits over firefighting foams into a single case — and whether to add others regarding pollution alleged near manufacturing sites.

3M Co., a maker of the chemicals, and Tyco Fire Products LP and Chemguard Inc., which have used them in firefighting foams, asked to consolidate the cases. DowDuPont Inc., which as DuPont used the chemicals to make Teflon, and its spinoff Chemours Co. are fighting against merging the litigation. They argue that such a large lawsuit would be “unprecedented and unwieldy,” given allegations the chemical is in 99 percent of the U.S. population. Plaintiffs — including towns, water districts and people with personal-injury claims — are split on consolidating the litigation.

“The delivery mechanisms are different,” Andrew Carpenter, a lawyer for DuPont and Chemours, told the panel.

Douglas Garrou, a lawyer for Georgia-Pacific LLC, which also doesn’t want consolidation, agreed. “Yes, it does matter what this chemical was contained in,” he said. For the paper maker, he said, the allegations are that oil and grease-resistant papers treated with the chemicals were improperly disposed of in landfills. In other cases, claims are over airborne pollution or disposal in rivers.

Municipal Water

At stake are potentially billions of dollars of claims against companies over a class of thousands of similar chemicals, known as PFAS (pronounced PEE-fas). If the suits fail, municipal drinking-water systems across the country could have to pay for filters to screen out PFAS, as some states tighten regulations and the Environmental Protection Agency debates new rules. If the lawsuits succeed, they could shake up supply chains. Besides being used to make electronics and the nonstick coating Teflon, the chemicals are in a wide range of household products, such as stain-repellent carpets, waterproof clothing and fast-food packaging.

Immune System

The cases could even determine whether there is new evidence of links between PFAS and cancers or damage to the immune system, as many lawsuits claim. One case from a firefighter, which seeks a class action on behalf of everyone with PFAS in their blood — an estimated 99 percent of the population — asks the courts to order a health study of exposed people.

The panel said Thursday it would rule later through a court filing.

Tyco and Chemguard face suits saying that their firefighting foams — known as AFFFs, or aqueous film-forming foams — contaminated groundwater with PFAS through use at airports and military bases. The companies asked to consolidate the suits in district court in Massachusetts or Manhattan.

3M — which sold PFAS for use in the AFFFs, and uses them in its own products, including Scotchgard — was named as a co-defendant in many suits. It wants to consolidate 15 of them with the AFFF cases, citing common questions, such as whether there is “scientifically reliable evidence” that connects PFAS to human health problems and whether federal or state governments knew about risks associated with the firefighting foams.

Health Study

DuPont and Chemours said the firefighter’s request for a health study make that case “fundamentally different” from the monetary claims sought in some of the firefighting foam litigation. They have already lost some suits over the chemicals — after such a study was done, and weighed by a judge.

The two companies together paid $671 million to settle thousands of personal-injury suits in a Columbus, Ohio, court. The rulings came after a similar study was done on people exposed to one of the chemicals, PFOA, which got into the water around a plant in West Virginia. The study monitored affected residents over time and concluded that PFOA was linked to six diseases, including kidney cancer, testicular cancer and ulcerative colitis.

Both companies say they also oppose consolidation because such a “mega” multidistrict litigation would “only increase the complexity, delay and inefficiencies” of the suits.

Which Court?

Arguments were also made on Thursday over which court should handle any consolidated case. 3M wants a joint suit to be heard by Judge Kenneth Karas in the Southern District of New York or by Judge Denise J. Casper of the District of Massachusetts. The firefighter wants his case assigned to Chief Judge Edmund Sargus of the Southern District Court of Ohio, who ruled against DuPont and Chemours in the cases that led to the $671 million settlement.

3M phased out some types of PFAS by 2002, while other companies, including DuPont, did so later. Since the most-studied types of PFAS don’t degrade, they are still found in sites where they were disposed of decades ago.

The case is In Re Aqueous Film-Forming Foams (AFFF) Products Liability Litigation, MDL Docket No. 2873, before the U.S. Judicial Panel on Multidistrict Litigation.