A federal judge presiding over more than 400 lawsuits claiming that glyphosate—the active ingredient in Monsanto's Roundup weed killer—causes cancer ruled Tuesday that the plaintiffs could present their evidence in court, ABC reported.

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U.S. District Judge Vince Chhabria said the evidence presented by experts in March hearings linking glyphosate to a type of cancer called non-Hodgkin's lymphoma were "not junk science" and could be heard by a jury. However he also said the evidence was "rather weak" and that lawyers faced a "daunting challenge" in convincing him to let the jury hear evidence linking individual cancer cases to glyphosate.

The plaintiffs' lawyers were pleased with the ruling.

"It's time to hold Monsanto accountable for putting this dangerous product on the market," lawyer Aimee Wagstaff told Reuters.

The lawyers representing Monsanto—which was recently purchased by Bayer and is set to lose its infamous name in the deal—were meanwhile heartened by Chhabria's skepticism.

"Moving forward, we will continue to defend these lawsuits with robust evidence that proves there is absolutely no connection between glyphosate and cancer," Monsanto Vice President Scott Partridge said in a statement reported by ABC. "We have sympathy for anyone suffering from cancer, but the science clearly shows that glyphosate was not the cause."

Glyphosate was linked to cancer by the World Health Organization's International Agency for Research on Cancer, which listed it as a "probable human carcinogen" in 2015.

However, U.S. agencies, including the Environmental Protection Agency (EPA) have concluded that glyphosate is safe if properly used. A 2017 National Institutes of Health study found no links between glyphosate and cancer.

Beate Ritz, a University of California, Los Angeles epidemiologist and one of the experts who will be allowed to testify, said in the March hearing that the NIH study was flawed and that her review of the research led her to conclude there was a credible link between glyphosate and non-Hodgkin's lymphoma.

Monsanto argued that the information presented by the plaintiffs' experts was not legally or scientifically admissible and urged Chhabria to dismiss the cases, Reuters reported.

There are 5,000 cases against Monsanto pending, mostly in state courts. While Chhabria's ruling has no direct bearing on the state cases, state judges, including one hearing the most Roundup cases in California, were following his expert hearings and Chhabria's decison, Reuters reported.

Lawyers in the first Roundup-related case to go to trial, brought by dying San Francisco groundskeeper Dewayne "Lee" Johnson, gave their opening statements Monday.