Bayer, which bought Monsanto for $63 billion in 2018, said it disagreed with the verdict and planned to pursue post-trial motions and, if necessary, an appeal.
"The undisputed evidence in this case does not support the conclusions that plaintiffs were exposed to unsafe levels of PCBs at the Sky Valley Education Center (SVEC) or that any exposure could have possibly caused their claimed injuries," Bayer said in a statement.
"In reality, testing reflected extremely low levels of PCBs in this school."
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.
The plaintiffs had alleged exposure to PCB at the SVEC from fluorescent light ballasts, which Bayer said were produced decades ago by customers of Monsanto's products and installed in the late 1960s.
"These light ballasts were decades beyond their useful life, energy inefficient, and obsolete," Bayer said.
"These are historic claims that relate to products Monsanto has not produced in more than 40 years and are unrelated to any ongoing business of Monsanto, and now Bayer."
In December, a U.S. federal judge rejected Bayer's proposed $648 million settlement of separate class-action litigation by cities and other claimants over waste water contaminated with PCBs made by Monsanto.
Bayer has submitted a revised settlement to the court and is confident that it will be approved, a spokesperson for Bayer said. The company expects a decision on the matter this summer.
(Reporting by Patricia Weiss; Writing by Maria Sheahan; Editing by Douglas Busvine and Jane Merriman)