(Reuters) - Washington state filed an environmental lawsuit on Thursday against agricultural company Monsanto Co seeking damages and cleanup costs associated with the company’s production of PCBs, the state’s attorney general said.

Monsanto's Roundup weedkiller atomizers are displayed for sale at a garden shop at Bonneuil-Sur-Marne near Paris, France, June 16, 2015. REUTERS/Charles Platiau/File Photo - RTX2QEAC

Monsanto produced the polychlorinated biphenyls, or PCBs, “for decades while hiding what they knew about the toxic chemicals’ harm to human health and the environment,” Attorney General Bob Ferguson said in a statement.

St. Louis-based Monsanto, whose products include genetically modified crop seeds and pesticides, said the lawsuit, which was filed in King County Superior Court, lacked merit.

“This case is highly experimental because it seeks to target a product manufacturer for selling a lawful and useful chemical four to eight decades ago that was applied by the U.S. government, Washington State, local cities, and industries into many products to make them safer,” Monsanto Vice President Scott Partridge said in a statement.

PCBs, once used widely to insulate electrical equipment and in products like paint and caulk, have been linked to cancer, immune system difficulties and other health problems.

The manufacture of PCBs was banned in the United States in 1979. Monsanto was the only U.S. producer of PCBs between 1935 and 1979, Ferguson said.

The lawsuit - against Monsanto and two of its splinter companies, Solutia Inc and Pharmacia LLC - seeks compensation for damages to Washington state’s natural resources, including the economic impact to the state and its residents, Ferguson said.

“PCBs have been found in bays, rivers, streams, sediment, soil and air throughout Washington state, with more than 600 suspected or confirmed contamination sites from Puget Sound to the Wenatchee River, Lake Spokane to Commencement Bay,” he said.

The company faces lawsuits by at least eight West Coast cities raising similar claims.

In September, German chemicals and healthcare group Bayer AG made an offer to buy Monsanto for $66 billion. The deal has to be cleared by regulatory authorities in the United States, Europe and elsewhere.