By Jonathan Stempel

(Reuters) – Los Angeles County sued Monsanto Co on Thursday, seeking to force the unit of Germany’s Bayer AG to help pay for reducing PCB contamination in dozens of bodies of water.

The most populous U.S. county, which has about 10.1 million people, said the presence of polychlorinated biphenyls (PCBs) in products sold by Monsanto many decades ago has caused widespread environmental contamination, forcing it to spend money to retrofit its stormwater systems and prevent further damage.

Los Angeles County said Monsanto had long concealed its knowledge that PCBs were harmful, and created a public nuisance because their presence interferes with commerce, fishing, navigation, swimming and other water-based activities.

Bayer did not immediately respond to requests for comment.

It said in its annual report in February that it had “meritorious defenses” against PCB-related claims.

Los Angeles County is seeking compensatory and punitive damages in its complaint filed in Los Angeles federal court.

It joined many other U.S. municipal entities to sue Monsanto over PCBs. Lawyers for the county did not immediately respond to requests for comment.

The lawsuit adds to Bayer’s legal problems relating to Monsanto, which it bought last year for $63 billion.

Bayer also faces claims by more than 13,400 plaintiffs that Monsanto’s Roundup weed killer causes non-Hodgkin’s lymphoma, and that Monsanto concealed the link.

A jury in Oakland, California, on May 13 awarded $2.055 billion to a couple who said Roundup caused their cancer, though that award will likely be reduced. Bayer has said Roundup is safe, and that several health regulators worldwide agree.

PCBs were once used widely to insulate electrical equipment, helping reduce fire risk, and were also used in such products as carbonless copy paper, caulking, floor finish and paint.

But they have also been linked to cancer, immune system difficulties and other health problems, and were outlawed by the U.S. government in 1979.

Monsanto produced PCBs from 1935 to 1977, and has said it stopped making them because they were not readily biodegradable.

The case is County of Los Angeles et al v Monsanto Co et al, U.S. District Court, Central District of California, No. 19-04694.

(Reporting by Jonathan Stempel in New York; Editing by Tom Brown)