Gramoxone, a pesticide that contains paraquat, at a local agriculture supply store in Hebron, Ohio. Last year, 7 million pounds (3.1 million kg) of paraquat were used in the US. Many nations that ban chemicals whose use is contentious still allow them to be manufactured as long as they are exported to faraway fields. Image Credit: The New York Times

Huddersfield, England: The factory here, set amid a brick campus in a green and hilly industrial town, recently celebrated its centennial.

It produces paraquat, one of the world’s most enduring weed killers — but not one that can be purchased in this part of northern England, in the rest of Britain or across the Channel in the rest of the European Union (EU).

So it will be sent to the US, or another part of the globe that still allows paraquat to be sprayed on weeds.

Paraquat has long been controversial because of its use in suicides in many parts of the world, since drinking even one sip can be lethal. But now regulators in the US are grappling with a wave of research linking paraquat to a less immediately apparent effect — Parkinson’s disease.

In a recent, little noticed regulatory filing, the Environmental Protection Agency (EPA) said, “There is a large body of epidemiology data on paraquat dichloride use and Parkinson’s disease.” The agency is weighing whether to continue allowing the chemical to be sprayed on American cropland, although a decision is not expected until 2018, and it is unclear how the incoming administration of Donald Trump will view the matter.

In the meantime, many of the nations that ban paraquat and other chemicals whose use is contentious still allow them to be manufactured as long as they are exported to faraway fields. The Huddersfield plant is owned by Syngenta, a pesticide giant based in Switzerland, which has not allowed paraquat since 1989.

Even the government of China, a nation not known for environmental regulation, said in 2012 that it would phase out paraquat “to safeguard people’s lives”. But it still allows production for export.

As Europe and China move away from paraquat, its use is rebounding in the US. That is particularly true for soybean fields, where the number of pounds used is up more than fourfold over the past decade, according to US Agriculture Department data.

The world’s most popular weed killer is Monsanto’s Roundup; some 220 million pounds of its active ingredient were used last year in the US, according to the EPA. But weeds are becoming resistant to Roundup, and paraquat has been marketed as an alternative. Last year, 7 million pounds (3.1 million kg) of paraquat were used in the US, on nearly 15 million acres, Syngenta said.

Paraquat is just one of scores of pesticides prohibited in Europe but sold outside it. In 2013, the EU imposed a moratorium on a widely used group of insecticides made by Syngenta and Bayer, the German giant, that were linked to a decline in bee colonies. In 2003, the EU banned one of the most popular weed killers in the US, Syngenta’s atrazine.

Industry officials and academics funded by agrochemical companies often criticise Europe’s regulators for taking a precautionary approach to regulation. They frequently claim that the risks of these various chemicals are well understood. But paraquat shows how complex the question of risk can be.

While the possibility of a Parkinson’s link has been cited in studies going back more than two decades, research in the past five years has intensified, including a prominent study by the National Institutes of Health and meta-analyses of a large body of research. The studies have looked at the exposure of farmers and others who spray paraquat, as well as people who live near where it is used, which can include nonagricultural settings like those around roads and rail tracks.

“The data is overwhelming” linking paraquat and Parkinson’s disease, said Dr. Samuel M. Goldman, an epidemiologist in the San Francisco Veterans Affairs health system who has studied the connection. “I’m not a farmer, I don’t need to kill weeds, but I have to believe there are less dangerous options out there.”

Syngenta has long rebutted the Parkinson’s link, and by no means is paraquat seen as a sole factor in the disease. Philip A. Botham, Syngenta’s head of product safety, said, “We would never market or continue to market any chemical which we genuinely felt posed a health risk or an environmental risk.”

As for studies drawing a connection between Parkinson’s and paraquat, he said, “Our view on those studies is that they are interesting — we don’t dismiss them — but they generate an interesting hypothesis which is worth exploring.”

When ingested by humans, paraquat is often fatal. South Korea experienced a 10 per cent decline in suicides after it banned paraquat in 2011, according to one study. Researchers in Taiwan have said it causes 160 deaths a year there.

Isabella Blow, an editor at the British magazine Tatler, died after drinking paraquat in 2007, the last year it was legal in Britain. She was not the first person in her family to die from drinking the weed killer.

The Parkinson’s question is more complicated. Symptoms of the disease, such as tremors and slowed movement, stem from a loss of nerve cells in part of the brain.

While the causes are not fully understood, it is typically viewed as stemming from a blend of environmental and genetic factors. Some research even draws a connection to gut bacteria. A wide variety of studies have linked paraquat and Parkinson’s, including epidemiological reviews that have looked at human disease patterns, studies involving experiments on rats, and research examining toxicity on a cellular level.

Some studies point to a combination of pesticides as a risk factor, and even well water in rural areas. Paraquat and another pesticide, rotenone, which is obtained from plant roots, are the ones most frequently linked to Parkinson’s. The use of rotenone in lakes and other water supplies has been contentious.

A 2011 study led by the Parkinson’s Institute and the National Institutes of Health drew on a federal survey of farmers and their spouses in Iowa and North Carolina, as well as others who handled pesticides. Those studied were two-and-a-half times more likely to develop Parkinson’s if they used paraquat or rotenone. A 2012 study found that those who used paraquat, and who also had a certain genetic variation, were 11 times more likely to develop Parkinson’s, suggesting that certain people could be more at risk from exposure than others.

“It’s a poison, and we really shouldn’t be using this as an herbicide in the way we do,” said Dr. Beate Ritz, a professor of epidemiology at the Fielding School of Public Health at the University of California, Los Angeles, who has studied health risks to people living near where pesticides are used.

Syngenta has been known for aggressively defending its products, including engaging in a bitter feud with a scientist whose research it once underwrote. The company argues that studies implicating paraquat do not adequately consider other environmental factors or chemicals that are present. Syngenta also studied the workforce at an old British manufacturing site that produced paraquat and found a lower-than-expected rate of Parkinson’s, though its study relied on death certificates, which often underreport the disease.

“I do believe paraquat is safe when it’s used appropriately,” said Botham of Syngenta. “I will, though, always as a scientist be open to any new findings.”

Dr Vikram Khurana, a neurologist at the Harvard Stem Cell Institute and a clinician at Brigham and Women’s Hospital who studies Parkinson’s, said the body of research drawing a link between paraquat and Parkinson’s had “converged to make a fairly convincing argument that paraquat is truly an environmental exposure that can either increase the risk of Parkinson’s disease or collaborate with other factors, including genetic factors.”


Making connections

Jack Housenger, director of the EPA’s pesticide programmes, said, “In terms of Parkinson’s disease, there’s a lot of data out there.”

“I’m not sure there’s any one study where there’s a direct link that’s been established here,” he added, “but given all the data, we’re incorporating all that in our next risk assessment.”

The business models of many chemical companies, including those based in Europe, have become predicated, in part, on keeping their products legal outside the Continent. This year, Britain has exported paraquat to Brazil, Colombia, Ecuador, Guatemala, India, Indonesia, Japan, Mexico, Panama, Singapore, South Africa, Taiwan, Uruguay and Venezuela, in addition to the US, according to the office of Britain’s Health and Safety Executive.

“This is one of the quintessential examples of double standards,” said Baskut Tuncak, a United Nations official who specialises in hazardous substances. “Paraquat is banned in the UK and the EU, but it’s still being used, and resulting in serious harms outside the EU where it’s being shipped.”

Tuncak said he had begun examining practices allowing companies to make pesticides exclusively for use outside their borders, seeing it as a potential human rights issue. He said paraquat would be “one of the issues that I plan to examine” during an official visit to Britain next month.

International efforts to regulate pesticides have been halting. Each year, government officials from around the world convene in Europe to discuss whether to add pesticides to a list of hazardous chemicals maintained as part of an international treaty called the Rotterdam Convention, a designation that creates disclosure requirements for exporting countries. A few countries, including Vietnam and Ecuador, automatically ban or restrict chemicals that are added to the list.


Little interest

Stark differences in national approaches are typically on full display. At a meeting last year in Rome, European regulators pushed to add atrazine, another Syngenta weed killer, to the list. But a government representative from India — which itself operates a pesticide manufacturer — was more voluble in defending atrazine than a Syngenta lobbyist who was present. The official even argued over technicalities, including how many weeks ahead of the Rome meeting supporting documents needed to be circulated.

In Huddersfield, local environmentalists no longer give much thought to the Syngenta factory. Even a chemical spill last year generated little interest.

Andrew Cooper, a Green Party member who serves on the local governing council, and whose district is a few kilometres from the plant, said activists were more worried about pollution from cars on a road abutting Syngenta’s main building on the site.

“There’s no impact that we can determine on the local community,” he said. “What they produce and what goes out the door, that’s a different matter, but it’s not something we campaign on much in recent years.” He added, “It has been off our radar.”