California will add glyphosate, the main ingredient in Monsanto’s blockbuster herbicide RoundUp, to its list of chemicals known to cause cancer, effective July 7, 2017. 
Monsanto promises to fight the listing, required under state law Proposition 65, calling the decision “unwarranted on the basis of science and the law.”
The seeds and chemical company unsuccessfully tried to block the listing in trial court and requests for stay were denied by a state appellate court and the state’s Supreme Court. Monsanto has appealed the trial court decision.
Monsanto is entrenched in legal problems at the moment, including hundreds of lawsuits filed by people who allege glyphosate caused them cancer. The biotech giant and its products have always been controversial, but the company’s problems snowballed after the World Health Organization’s International Agency for Research on Cancer (IARC) declared the chemical “probably carcinogenic” to humans.
In addition, the U.S. Environmental Protection Agency’s (EPA) inspector general is currently investigating whether a former staffer colluded with Monsanto to “kill” a study linking glyphosate to cancer.
Scott Partridge, Monsanto’s vice president of global strategy, said:
“This is not the final step in the process, and it has no bearing on the merits of the case. We will continue to aggressively challenge this improper decision.”
Glyphosate’s designation as a carcinogen under Proposition 65 means that companies selling the weed-killing chemical in California would be required to add warning labels to packaging. Additionally, warnings will need to be issued if glyphosate is sprayed at levels deemed harmful by regulators. The majority of glyphosate applicators are landscapers, golf courses, orchards, vineyards, and farms.
Monsanto and other glyphosate manufacturers will have about a year from the listing date to add the warnings to their products or pull them from the market if it is unsuccessful in challenging the decision.
It’s not clear whether RoundUp will receive a warning label. State regulators must still decide if the name brand weed killer contains high enough levels of glyphosate to endanger human health. More than 1,300 public comments have flooded state regulators on the matter. 
Sam Delson, a spokesman for California’s Office of Environmental Health Hazard Assessment (OEHHA), said:
“We can’t say for sure. We’re reviewing those comments.”
Glyphosate, an odorless, colorless chemical, was introduced by Monsanto in 1974, and skyrocketed in popularity for its ability to kill weeds without harming other plants. It is sold in 160 countries, and it is applied to 250 types of crops in California alone.
The fight to protect Californians from toxic substances like glyphosate is far from over, says Michael Baum, an attorney who represents more than 300 people who have filed suit against Monsanto, claiming glyphosate caused a loved one to get sick or die due to exposure to RoundUp.
Nathan Donley, a former cancer researcher and senior scientist at the Center for Biological Diversity, an environmental group, in an emailed statement, echoed similar sentiments. He said:
“California’s decision makes it the national leader in protecting people from cancer-causing pesticides. The U.S. EPA now needs to step up and acknowledge that the world’s most transparent and science-based assessment has linked glyphosate to cancer.” 
 ABC News