By Brendan Pierson and Dietrich Knauth

January 14 (Reuters) - A Washington state jury on Tuesday said Bayer must pay $100 million to four people who say they were sickened by exposure to toxic chemicals known as PCBs made by the company's predecessor Monsanto that were used in light fixtures at a Seattle-area school, but found that the company was not liable for injuries alleged by ten others, according to a lawyer for the plaintiffs.

The verdict in a Washington state court, which follows a two-month trial, is the latest in a string of trial losses for the chemical company over the alleged contamination at the Sky Valley Education Center in Monroe, Washington.

More than 200 students, employees and parents have said they developed cancer, thyroid conditions, neurological injuries and other health problems from polychlorinated biphenyls or PCBs leaking from the school's light fixtures.

Verdicts in previous trials over the alleged contamination at the school, which have involved different groups of plaintiffs, totaled more than $1.5 billion, though some have been reduced or overturned.

Bayer got a verdict for $185 million in favor of three teachers and a teacher's spouse, overturned on appeal last year on multiple grounds. The state appeals court agreed with Bayer that the trial court wrongly applied the laws of Missouri, where Monsanto was based, allowing the claims to be filed decades after the company stopped producing PCBs in 1977. The company said Washington law should apply instead, and it would block the plaintiffs' claims as filed too late.

Washington's highest court is expected to hear an appeal of that ruling.

In August, an $857 million verdict was slashed to $438 million, after a judge found that it included excessive punitive damages.

Bayer acquired Monsanto for $63 billion in 2018. Since then, lawsuits over PCBs, and more significantly over claims that the weedkiller Roundup caused cancer, have weighed heavily on the company's shares.

PCBs were once used widely to insulate electrical equipment, and were also used in such products as carbonless copy paper, caulking, floor finish and paint. They were outlawed by the U.S. government in 1979 after being linked to cancer and other health problems. Monsanto produced PCBs from 1935 to 1977.

Plaintiffs have said that Monsanto knew of the dangers of PCBs for decades, but concealed them from the public and from government regulators.

Bayer has argued that plaintiffs have failed to prove that their injuries were caused by PCBs, and that the levels found in the school were deemed safe by the Environmental Protection Agency. It has also said that the school ignored warnings from government officials that the light fixtures in the aging building needed to be retrofitted.

(Reporting By Brendan Pierson and Dietrich Knauth in New York, Editing by Alexia Garamfalvi and Lisa Shumaker)