Agribusiness giant ordered to pay damages to man who says he got terminal illness after using popular weed killer.

A California jury has ordered chemical giant Monsanto to pay nearly $290m for failing to warn a dying groundskeeper that its weed killer Roundup might cause cancer.

Jurors on Friday unanimously found that Monsanto acted with malice and that its weed killers Roundup and the professional grade version Ranger Pro contributed “substantially” to Dewayne Johnson’s terminal illness. It also said the company should have provided a label warning of the potential health hazard.

Following eight weeks of trial proceedings, the San Francisco jury ordered Monsanto to pay $250m punitive damages, along with compensatory damages and other costs, bringing the total figure to nearly $290m.

“This jury found Monsanto acted with malice and oppression because they knew what they were doing was wrong and doing it with reckless disregard for human life,” said Robert F Kennedy Jr, a member of Johnson’s legal team. “This should send a strong message to the boardroom of Monsanto.”

The company, which has denied any link between the glyphosate, the active ingredient in Roundup, and cancer, vowed to appeal the verdict and “vigorously” defend its product.

Plaintiff Dewayne Johnson (L) reacts while his lawyer during the Monsanto trial [Josh Edelson/Reuters]

Johnson used Roundup and a similar product, Ranger Pro, as a pest control manager at a San Francisco Bay Area school district, his lawyers said. He sprayed large quantities from a 50-gallon (about 3.8 litres) tank attached to a truck, and during gusty winds, the product would cover his face, said Brent Wisner, one of his attorneys.

Once, when a hose broke, the weed killer soaked his entire body.

Johnson read the label and even contacted the company after developing a rash but was never warned it could cause cancer, Wisner said. He was diagnosed with non-Hodgkin’s lymphoma in 2014 at age 42.

“The simple fact is he is going to die. It’s just a matter of time,” Wisner told the jury in his opening statement last month.

Looming wave of similar lawsuits

The lawsuit is the first to accuse the product of causing cancer but is a may foreshadow possible outcomes of a looming wave of similar legal challenges. Observers also say a Monsanto defeat likely opens the door to hundreds of other claims against the company, which was recently acquired by Germany’s Bayer.

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The lawsuit built on the conclusions in 2015 of the International Agency for Research on Cancer, a part of the UN World Health Organization (WHO), which classified Roundup’s main ingredient glyphosate as a probable carcinogen, causing the state of California to follow suit.

However, the US Environmental Protection Agency (EPA) says Roundup’s active ingredient is safe for people when used in accordance with label directions.

Roundup is Monsanto’s leading product and glyphosate is reportedly the world’s most commonly used weed killer.