There are new calls to investigate the health effects of those using Roundup. 

A US court has ordered the weedkiller's manufacturer Monsanto to pay $2 billion after a couple successfully argued it's to blame for their cancer.

The state court jury in Oakland concluded that Monsanto's weed killer caused the non-Hodgkin's lymphoma Alva Pilliod and Alberta Pilliod each contracted. Jurors awarded them each $1 billion in punitive damages in addition to a combined $55 million in compensatory damages.

Alberta Pilliod, 76, said after the verdict that she and her husband, Alva, have each been battling cancer for the last nine years. She says they are unable to enjoy the same activities they participated in before their cancer diagnosis.

The jury's verdict is the third such courtroom loss for Monsanto in California since August.

Massey University public health expert Dr Dave McLean told Heather du Plessis-Allan we know it's probably capable of causing cancer, but little else. 

"What we don't know is how many people are exposed and to what level and we don't really know what happens to it once its in the body." 

He says there has been very little research done on the subject, nor is there a continued wide-spread study examining the effects.

However, he notes that breathing it after spraying has been found to be potentially dangerous. 

"It doesn't go through the skin that easily, so avoid contact."

Dr McLean says that the most prudent matter is to work out the effects on those whose work sees them exposed to the chemicals. 

He says he has used it before, and would likely use it again. 

The three California trials were the first of an estimated 13,000 plaintiffs with pending lawsuits against Monsanto across the country to go to trial. St. Louis-based Monsanto is owned by the German chemical giant Bayer A.G.

Bayer said Monday that it would appeal the verdict.

"The verdict in this trial has no impact on future cases and trials, as each one has its own factual and legal circumstances," the company said.

Monsanto noted that none of the California verdicts has been considered by an appeals court and that the U.S. Environmental Protection Agency considers the weed killer safe.

The EPA reaffirmed its position in April, saying that the active ingredient glyphosate found in the weed killer posed "no risks of concern" for people exposed to it by any means — on farms, in yards and along roadsides, or as residue left on food crops.