Monsanto, the agro-chemicals company, is facing a surge in lawsuits that could cost parent company Bayer (ETR: BAYN) billions in damages.

The number of US lawsuits against the company has jumped to an estimated 8,000 over the alleged cancer risks of the group’s glyphosate-based weedkillers.

Chief executive Werner Baumann said that at the time of acquisition, Bayer “could not foresee the scope of the current lawsuits.”

The deal was worth $63 billion completed earlier this month.

“In the course of the acquisition, we carried out due diligence as is standard practice when taking over a listed company. In doing so, we of course also considered the legal risks,” he said.

“The number of plaintiffs in both state and federal litigation is approximately 8,000 as of end-July. These numbers may rise or fall over time but our view is that the number is not indicative of the merits of the plaintiffs’ cases,” he added in a conference call on Thursday.

Last month the group lost $289 million (£225 million) to a court case where its products Roundup and RangerPro had led to a man’s terminal cancer.

Shares in the group have lost 11 percent since it lost this case over the groundskeeper Dewayne Johnson. Shares in Bayer fell a further 1.7 percent on Thursday.

Liam Condon, head of Bayer’s Crop Science division said: “Nothing whatsoever has changed in the regulatory status of the product. There is simply very high demand, and has been for many decades, for glyphosate. It is an invaluable tool for growers.”

Scientifically, the opinion is divided. The US Environmental Protection Agency concluded last year that that glyphosate is not likely to be carcinogenic to humans.

The World Health Organization classified glyphosate as “probably carcinogenic to humans,” in 2015.