SAN FRANCISCO (CBS)– Lawyers for a school groundskeeper dying of cancer asked a San Francisco jury on Monday to find that agribusiness giant Monsanto’s widely used weed killer Roundup likely caused his disease.

Dewayne Johnson’s lawsuit is the first case to go to trial among hundreds of lawsuits saying Roundup caused non-Hodgkin’s lymphoma.

Johnson sprayed Roundup and a similar product, Ranger Pro, at his job as a pest control manager at a San Francisco Bay Area school district, according to his attorneys.

He sprayed large quantities from a 50-gallon tank attached to a truck, his attorney, Brent Wisner, told jurors during his opening statement. When the wind was gusty, it would cover his face, Wisner said. When a hose broke once, it soaked his entire body.

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

“The simple fact is he is going to die. It’s just a matter of time,” Wisner said, showing jurors photos of lesions on Johnson’s body that he said were caused by cancer. Johnson sat nearby.

monsanto Monsantos Weed Killer Roundup Goes To Trial

Roundup products are seen for sale at a hardware store in San Rafael, California, on July, 9, 2018. – A lawyer for a California groundskeeper dying of cancer took aim at Monsanto on July 9, 2019 as a jury began hearing the lawsuit accusing the chemical giant of ignoring health risks of its top-selling weed killer Roundup. (Photo by JOSH EDELSON / AFP) (Photo credit should read JOSH EDELSON/AFP/Getty Images)

Wisner added, “Between now an then, it’s just nothing but pain.”

George Lombardi, an attorney for Monsanto, said non-Hodgkin’s lymphoma takes years to develop, so Johnson’s cancer started well before he began working at the school district.

Many government regulators have rejected a link between the active ingredient in Roundup — glyphosate — and cancer. Monsanto has vehemently denied such a connection, saying hundreds of studies have established that glyphosate is safe.

“The scientific evidence is overwhelming that glyphosate-based products do not cause cancer and did not cause Mr. Johnson’s cancer,” Lombardi said during his opening statement.

The trial is expected to last about a month. Johnson is seeking unspecified damages against Monsanto.

If it loses this battle, Monsanto and its new corporate parent, German chemical giant Bayer, which closed its $60 billion acquisition earlier this month, could face billions in lost revenue. Monsanto doesn’t break out sales of glyphosate, Roundup delivered $4.8 billion in revenue in 2015. In its latest fiscal year, Monsanto cited higher global sales of glyphosate for helping lift total revenue by 8 percent.

monsanto roundup trial Monsantos Weed Killer Roundup Goes To Trial

Plaintiff Dewayne Johnson listens as attorney Brent Wisner (out of frame) speaks about his condition during the Monsanto trial in San Francisco, California on July, 09, 2018. – Monsanto is being accused of hiding the dangers of its popular Roundup products. (Photo by JOSH EDELSON / AFP) (Photo credit should read JOSH EDELSON/AFP/Getty Images)

The outcome of Johnson’s case will not affect the hundreds of other lawsuits in state and federal courts, but it may serve as an indicator of how the others might go.

St. Louis-based Monsanto developed glyphosate in the 1970s, and the weed killer is now sold in more than 160 countries. Farmers in California, the most agriculturally productive state in the U.S., use it on more than 200 types of crops. Homeowners use it on their lawns and gardens.

The herbicide came under increasing scrutiny after the France-based International Agency for Research on Cancer, which is part of the World Health Organization, classified it as a “probable human carcinogen” in 2015.

A flurry of lawsuits against Monsanto in federal and state courts followed, and California added glyphosate to its list of chemicals known to cause cancer. Monsanto has attacked the international research agency’s opinion as an outlier.

The U.S. Environmental Protection Agency says glyphosate is safe for humans when used in accordance with label directions. A draft report by the agency last year concluded the herbicide is not likely to be carcinogenic to humans. The report noted that science reviews by numerous other countries had reached the same conclusion.

A federal judge in Sacramento in February blocked California from requiring that Roundup carry a label stating that it is known to cause cancer, saying the warning is misleading because almost all regulators have concluded that there is no evidence glyphosate is carcinogenic.

Another federal judge presiding over hundreds of lawsuits like Johnson’s is deciding whether the claim that Roundup weed killer can cause cancer is supported by good science.

Monsanto isn’t relying only on the courts to prove its case. Kantar Media said the company also boosted advertising about Roundup and its safety in 2018’s first quarter by 17 percent, reaching $5.6 million in spending, compared with a year earlier.