Pesticide giant ignored warnings over ineffective safety measures used in world’s deadliest weedkiller, investigation reveals

Internal documents and a whistleblower reveal how global pesticide giant Syngenta and its predecessors knew for decades that a key 'safety' feature in its lethal paraquat-based weedkillers did little or nothing to prevent poisoning deaths – but continued to present it as effective to regulators and the public.


A cache of internal documents reveals how global pesticide giant Syngenta – and its predecessor companies (ICI and Zeneca) – has known for decades that a key safety feature in the world’s deadliest weedkiller fails to prevent poisoning deaths but that it led regulators and the public to believe it was effective, a new investigation from Unearthed and Public Eye reveals.

The news comes as a whistleblower – senior toxicologist Professor Jon Heylings, who worked for Syngenta and its predecessors for 22 years – speaks out about how his warnings about the failings of this safety measure, and the “fabricated” report it was based on, were never acted upon by the company.

Read the full investigation

Paraquat is the most lethal weedkiller in the global market. Just one sip is enough to kill an adult human and there is no antidote. It is estimated to have caused tens of thousands of deaths worldwide since its introduction in the 1960’s, due to its use in suicides, as well as accidental ingestion – including by children mistakenly drinking it when decanted into soft drinks bottles. It is banned from use in more than 50 countries, including the UK.

Despite this, Syngenta still manufactures thousands of tonnes of paraquat every year in its factory in Huddersfield, which is then shipped to other countries around the world, including India, South Africa and the US, where it is used in weedkiller formulations. More than 28,000 tonnes of paraquat mixtures were notified for export from the UK by Syngenta in 2018 [2].

In order to make the product ‘safer’, Syngenta and its predecessor companies have been adding half a gram of an emetic – a vomit-inducing drug – to every litre of its paraquat-based weedkiller, Gramoxone, since the late 1970’s. The idea was to reduce the product’s toxicity by causing people who swallowed it to vomit out the paraquat before a fatal dose could be absorbed into the bloodstream.

However, internal documents – seen by Greenpeace UK’s investigative journalism unit, Unearthed, and Swiss NGO, Public Eye – reveal how Syngenta and its predecessors knew for decades that the emetic did little or nothing to prevent deaths from paraquat poisoning – but continued to present it as effective to regulators and the public.

The documents reveal how:

  • in the 1980’s and 1990’s it was not company strategy to “proactively” make costly safety improvements to its paraquat formulations;
  • that less-toxic formulations were developed and kept “on the shelf”, to be offered only to countries that were threatening to ban or restrict the chemical;
  • that the patented emetic additive was used as a way of blocking competition from other paraquat manufacturers;
  • that the company did this despite knowing it had no evidence the emetic would save lives at the concentration in which it was added;
  • that widespread introduction of safety measures like dilution were resisted because they were not considered to be “economically acceptable” solutions to “the suicide problem”;
  • and that it was repeatedly told by its own scientists that the amount of emetic in Gramoxone was too low to prevent fatal poisonings.

Professor Jon Heylings led work to develop safer formulations of paraquat during his 22-year career at Syngenta and its predecessors. Internal documents show he first raised the alarm about what he considers to be an “ineffective” level of emetic used in Gramoxone in 1990 after discovering, what Professor Heylings describes as, a “fabricated” internal report from 1976.

According to Heylings the report manipulated data to wrongly suggest that the emetic was much more effective in humans than it was in the animals ICI tested it on.

In memos to his superiors at the time Professor Heylings informed them that the report had “grossly misled” the company, that the concentration recommended was “probably well below an effective emetic dose in man”, and that he thought a sharp increase in the concentration of emetic in Gramoxone could “reduce the number of fatalities attributed to paraquat poisoning”.

But the company did not share these concerns with the public or regulators and, to this day, Syngenta still manufactures Gramoxone with the same level of the emetic as it has since the 1970s.
The company has also persuaded the Food and Agriculture Organisation of the United Nations (FAO) to adopt this concentration as a global specification, in the agency’s guidance on the standards all paraquat-based weedkillers should meet.

When Heylings – who is now an honorary professor of toxicology at Keele University – discovered in 2018 that the FAO was still using Syngenta’s “ineffective” emetic specification, he again tried to sound the alarm, first in meetings and correspondence with Syngenta, then with the FAO and the US Environmental Protection Agency (EPA).

In an email to the FAO in 2019, he wrote: “I have nothing against Syngenta. I just want the next child that accidently takes a sip of paraquat weed-killer to have a fighting chance of survival by vomiting the poison out before a lethal dose is absorbed into the blood and they die of pulmonary failure.”

In an interview with Unearthed and Public Eye, Professor Heylings, said: “I want to be able to look back with my own grandchildren and say, ‘I’m glad I did that’. I know it took a long time to get the message through. I tried my best in the early 1990s, but I’m trying again now to convince Syngenta that they were wrong with the emetic concentration. And that’s what’s keeping me going.”

Professor Heylings did create a different formulation during his time at Syngenta, which was trialled in Sri Lanka in the early 2000’s. It contained a three fold increase in the emetic – lower than the five fold increase that he wanted but which was resisted by others in the company because of the high cost of the emetic.

While the formulation with a higher emetic content did slightly reduce the death rate during a key trial, it did not save enough lives to prevent paraquat from becoming banned in the country.

Today, Gramoxone sold in the US has an emetic content roughly three times higher than standard Gramoxone. Whereas the original low-emetic formulation is still sold in most other markets – particularly in low-to-middle income countries, such as India.

Greenpeace UK’s chief scientist, Doug Parr, said: “Despite the tens of thousands of lives lost to this deadly weedkiller, Syngenta have failed to make the product safer to protect their bottom line.

“Poorer nations being exploited by corporate greed is nothing new but this abhorrent behaviour really shows how far pesticides giants are willing to go in order to prioritise profit over people and the planet. Nor can this be dismissed by Syngenta as something that happened decades ago – it is still going on to this day.

“At the very least the UK government must put an immediate stop to the morally indefensible production and export of paraquat from this country. And ultimately, we need a global ban on this deadly pesticide.”


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  1. Thousands of tonnes of banned pesticides shipped to poorer countries from British and European factories

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