(Reuters) - DuPont ( DD ), 3M ( MMM ), Honeywell ( HON ) and 16 other defendants were sued on Tuesday by Connecticut firefighters who said their protective gear was contaminated by toxic "forever chemicals" linked to cancer.

Lawyers for the plaintiffs said they believed the proposed class action filed in the New Haven, Connecticut federal court is the first to exclusively target firefighter gear containing per- and polyfluoroalkyl substances, or PFAS.

The Uniformed Professional Fire Fighters Association of Connecticut, five other unions and five firefighters sued on behalf of firefighters across the state, including cities such as Hartford and Stamford.

They said jackets, pants and other "turnout gear" leeched PFAS into firefighters through their skin, ingestion and inhalation, and that more PFAS is absorbed as temperatures rise and sweat builds up.

The plaintiffs said that led to "subclinical cellular changes in their bodies which put them at increased risk of developing adverse health conditions," justifying at least $5 million of damages for violations of Connecticut product liability law.

DuPont ( DD ) and 3M ( MMM ) produced PFAS used in the protective gear, while a Honeywell ( HON ) subsidiary was among the gear's sellers, and failed to warn of the risks, the complaint said.

In a statement, DuPont ( DD ) said the lawsuit was without merit, and that "we look forward to vigorously defending our record of safety, health and environmental stewardship."

DuPont ( DD ) also said it has never manufactured PFOA and PFOS, which are two types of PFAS that the plaintiffs alleged were used in their gear.

Neither 3M ( MMM ) nor Honeywell ( HON ) immediately responded to requests for comment.

PFAS are found in hundreds of consumer and commercial products including cosmetics, non-stick pans and stain-resistant clothing.

They earned the sobriquet "forever chemicals" because they do not break down easily in the human body or environment.

PFAS have been linked to negative health effects including higher cholesterol, low birth weights and reduced antibody response to vaccines, as well as kidney and testicular cancer.

Last year, DuPont ( DD ), 3M ( MMM ) and two other companies reached more than $11 billion of settlements to resolve claims that firefighting foam and other products containing their PFAS polluted drinking water. None admitted wrongdoing.

The case is Uniformed Professional Fire Fighters Association of Connecticut et al v 3M Co ( MMM ) et al, U.S. District Court, District of Connecticut, No. 24-01101.