Around the world, the deadly dangers of a weedkiller called paraquat are well known...

Switzerland, the home base of the paraquat maker Syngenta, has banned the chemical since 1989, and it has been banned for use in the EU since 2007, because of paraquat’s deadliness.

The US Environmental Protection Agency (EPA) allows only restricted use of the pesticide in the United States by people certified and trained to apply it, such as landscapers and farmers...

Paraquat exposure is also believed by some scientists to cause Parkinson’s disease, and Syngenta is facing litigation on that issue – though it denies responsibility.

Still, many countries allow wide use of paraquat, and the toll from paraquat poisonings is estimated at well into the thousands. The low cost and high toxicity makes paraquat a popular poison for people trying to kill themselves...

But now, internal corporate documents, obtained by a US law firm and provided to the Guardian, detail how the need for a safer formulation of Syngenta’s popular Gramoxone paraquat-based product has been the subject of in-depth company discussions for decades. Years of analysis and debate over the issue are laid out in the records, as are arguments about the accuracy of data presented to regulators, and strategies to avoid regulatory bans.

The documents, which date back to 1968, show that Syngenta and its predecessor corporate entities rejected or resisted many different options for changes to the formulations of Gramoxone, due, at least in part, to a desire to protect profits. Financial concerns were cited repeatedly in the discussions about formulation changes as company officials pushed to keep Gramoxone on the market despite mounting concerns about fatalities.

The documents also show that a longtime Syngenta scientist, who left the company in April 2008 after 28 years, argued with company officials multiple times over his belief that lives could have been saved with tweaks to product formulations that he said Syngenta considered too costly to make.

That scientist, Jon Heylings, formerly the head of research and investigative toxicology at Syngenta, accuses his former employer and Syngenta’s predecessor companies of relying on data generated in the 1970s that, according to Heylings, misrepresented the amount of an additive that could potentially make Gramoxone less deadly.

Heylings told the company more of the additive was needed than was stated. But his concerns were rejected and a product he developed that he believed was safer was shelved...

Syngenta told the Guardian that Heylings’ allegations were meritless, and said the company was “absolutely committed” to ensuring its products are used safely. “Heylings is now turning to the media because his views have not been accepted by Syngenta or the regulatory bodies he approached and are not supported by modern medical science as well,” the firm said.

Heylings is now working with the environmental organization Greenpeace to publicize his accusations and alert regulators. He sent his allegations to the EPA and to the Food and Agriculture Organization of the UN (FAO)...