Animal studies in favor of Roundup had only been conducted within a span of 90 days or less. In addition, short-term trials or trials using just glyphosate alone were used as a basis to market Roundup. True enough, Monsanto used a 90-day study conducted in 2004 as a basis for Roundup's regulatory approval.
These short-term trials served two purposes for Monsanto. First, it did not allow further analysis of the other chemicals in Roundup. Second, it prevented the observation of tumor formation in animals – which usually occurred at about 100 days. Keeping the trials at 90 days or less, before tumors started to develop in animals, allowed Monsanto to promote Roundup as non-carcinogenic.
However, French scientist Gilles-Eric Seralini took Monsanto's study further. He extended the 2004 study's 90-day duration to two years, which is the ordinary life span of rats. He fed one group of rats with corn genetically modified to resist glyphosate and water laced with the herbicide. On the other hand, he fed another group of rats – the control group – regular corn and water.
Seralini found that 80 percent of rats that consumed Roundup for two years developed tumors, compared to only 30 percent in the control group. He also found that rats who consumed glyphosate had larger tumors – between 30 percent and 130 percent – compared to the control group. His findings ultimately suggested that Roundup did cause cancer, contrary to the common belief at that time.
The study by Seralini and his colleagues was initially published in September 2012 in Food and Chemical Toxicology (FCT). However, the study threatened Monsanto's billion-dollar profits from Roundup.
When the study's findings came out, Monsanto moved quickly to attack Seralini to preserve Roundup's market share. The company had purposely avoided or cleverly navigated regulatory tests that would have otherwise proven that Roundup was cancerous. Thus, Monsanto set out to suppress the glyphosate-based herbicide's critics instead of alerting the population about its dangers.
Seralini exposed Monsanto's campaign against him in a book titled "The Monsanto Papers: The Truth Behind the Corruption and Misrepresentation of Science at the Cost to Public Health," alongside fellow scientist Jerome Douzelet. He presented documents proving Monsanto's involvement in the manipulation of peer reviews and ghostwriting articles that downplayed the dangers of Roundup.
The scientist also revealed in the book that FCT's editor A. Wallace Hayes had signed a consultancy contract with Monsanto before the study's September 2012 publication. Based on documents Seralini presented in the book, the consulting agreement between Hayes and Monsanto was dated from August 2012. The agreement stipulated that Hayes would provide his services beginning the next month – a clear conflict of interest.
Seralini also elaborated how Monsanto used "letters to the editor" campaigns to suppress his study. The campaigns made use of scripted talking points that looked like scientific experts taking umbrage at its findings, he said.
He continued that his paper received criticism from these "experts" that said it was flawed and improperly peer-reviewed. Said experts also called him out for using cancer-prone rats for his study. FCT eventually gave in to the criticism retracting the study in 2013.
Before Seralini turned in his now-retracted 2012 paper to FCT, he finished an earlier study in 2009 that focused on human liver cells exposed to Roundup. The French scientist submitted this paper to Regulatory Toxicology and Pharmacology (RTP). However, Monsanto toxicologist William Heydens was asked to conduct a peer review of this study – a clear conflict of interest.
Instead of maintaining the paper's confidentiality, he shared it with three members of the company's Freedom to Operate (FTO) team – Donna Farmer, David Saltmiras and Steven Levine. They synthesized their comments about Seralini's study in what was called "excellent rebuttal material" that ultimately recommended that the study be rejected.
The Monsanto team's efforts paid off, with RTP editor-in-chief Dr. Gio Batta Gori turning down the French scientist's paper for publication. When Gori told the news to Seralini, he did not disclose that Heydens was a principal peer reviewer of his paper. Meanwhile, Heydens shared the "good news" with the rest of the FTO team.
The concerning findings about Roundup later returned to haunt Monsanto. The World Health Organization's International Agency for Research on Cancer analyzed glyphosate in 2015 and found that it was indeed a probable human carcinogen. German chemical company Bayer eventually purchased Monsanto in 2018 for $66 billion.
Bayer's acquisition of Monsanto did little to alleviate the situation caused by Roundup. The company has had to shell out $2.4 billion in jury awards in three consecutive trials and $10.5 billion in settlements. Bayer also faced repeated losses in court over its appeals against injunctions.