A California groundskeeper dying of cancer is slated to testify Monday before jurors hearing evidence in his lawsuit blaming Monsanto weed killer Roundup for his terminal illness.
The first-of-its-kind trial pitting 46-year-old Dewayne Johnson against the agrichemical colossus is expected to last into August.
"For the past 40 years, Monsanto has known the primary ingredient in Roundup can produce tumors in lab animals," Johnson's attorney Brent Wisner said during opening remarks to jurors.
California law calls for products containing chemicals known to cause cancer to have warning labels.
Johnson's lawyer told jurors the father-of-two would not have used the weed-killer if it came with a warning label regarding cancer risk.
Monsanto countered in court that no such warning was needed, saying no link to cancer has been confirmed.
The legal clash involves dueling studies, along with allegations Monsanto connived behind the scenes to thwart potentially damning research,
Diagnosed in 2014 with non-Hodgkin's lymphoma, a cancer that affects white blood cells, Johnson used a Monsanto generic version of Roundup called "Ranger Pro" repeatedly in his job at a school in Benicia, California, after being promoted to groundskeeper in 2012.
In his opening statement, Wisner said Monsanto opted against warning consumers of the risks and that instead "they have fought science" by playing down the suspected link between the herbicide and cancer.
"Monsanto has gone out of its way to bully scientists and fight researchers," he told the jury.
The case in California Superior Court is the first trial in which Roundup is said to have caused cancer, a claim repeatedly denied by the chemical company.
If Monsanto loses, the case could open the door to hundreds of additional lawsuits against the company recently acquired by German-based pharmaceutical and chemical group Bayer.
- 'Told you could drink it' -
Johnson had little warning about the risks of Roundup, his lawyer said.
"He was told you could drink it, it was completely non toxic," Wisner said with his client sitting in the San Francisco courtroom.
"You will hear testimony from him that he got drenched in it, repeatedly."
The lawyer said Johnson, who is between rounds of chemotherapy, "is actually on borrowed time, he is not supposed to be alive today."
A key to Johnson's case will be convincing jurors that Monsanto's pesticide -- whose main ingredient is glyphosate -- is responsible for the illness. Wisner contended glyphosate combined with an ingredient intended to help it spread over leaves in a cancer-causing "synergy."
Whether glyphosate causes cancer has been the source of long debate among government regulators, health experts and lawyers.
Monsanto has denied any link with the disease and says studies have concluded the product is safe.
"Mr Johnson's cancer is a terrible disease. We all do and we all should have great sympathy for what he is going through," Monsanto defense attorney George Lombardi said during opening remarks in court.
"The scientific evidence is overwhelming that glyphosate-based products do not cause cancer, and did not cause Mr Johnson's cancer."
Monsanto's flagship herbicide Roundup was launched in 1976.
Roundup has been approved the US Environmental Protection Agency, according to Lombardi.
In 2015, the International Agency for Research on Cancer -- a World Health Organization body -- classified glyphosate as "probably carcinogenic," and as a result the state of California listed it as carcinogenic.
Founded in 1901 in St Louis, Missouri, Monsanto began producing agrochemicals in the 1940s. It was acquired by Bayer for more than $62 billion in June.