The trouble with our favourite weedkiller
It’s a widely used herbicide, but in recent years glyphosate has been the subject of nationwide protests, billion-dollar lawsuits, and Japan has turned away New Zealand honey because of it. Katy Jones reports.
Glyphosate is the world’s most commonly used herbicide. In New Zealand, it is used to kill weeds in places ranging from orchards, crops and vineyards, to private gardens, roadsides and public parks.
The herbicide is contained in hundreds of products globally, and used in about 90 products in this country, with Roundup arguably the most recognised brand.
Glyphosate now underpins much of New Zealand’s – and the world’s – food production.
Why do we use glyphosate?
Glyphosate was discovered to be a herbicide in 1970, by a chemist at American agrochemical corporation Monsanto.
The chemical works by blocking an enzyme present in plants (not in animals), which plants need to survive.
Monsanto brought glyphosate to the market in 1974, under the Roundup trade name. It was quickly adopted in the agriculture sector, as it enabled farmers to kill weeds without killing their crops.
Ecologists are now among those who use it for land-restoration projects.
But glyphosate has been mired in controversy over the past six years, since it was linked to cancer.
Courts in the United States have subsequently ordered Monsanto to pay millions of dollars in damages to people who claimed the weedkiller caused their non-Hodgkin’s lymphoma.
What do the scientists say?
In 2015 the World Health Organisation’s International Agency for Research on Cancer (IARC) classified glyphosate as ‘‘probably carcinogenic in humans’’, prompting several countries to ban or restrict its use.
But that wasn’t the end of it. Subsequent reviews by international bodies either contradicted that, or were inconclusive.
The European Food Safety Authority (EFSA) found that glyphosate was unlikely to pose a carcinogenic threat to humans.
And in 2016, the WHO and Food and Agriculture Organisation joint committee on pesticide residues said the use of glyphosate formulations did not necessarily constitute a health risk, and gave an acceptable daily intake.
What is New Zealand’s position on glyphosate?
In line with regulatory authorities in the US, European Union, Australia and Canada, New Zealand’s Environmental Protection Authority (EPA) said in 2016 that glyphosate was safe to use when the rules around its use were followed.
An amount of glyphosate residue is permitted in food.
The highest level allowed in food, grown in New Zealand, is 0.1 parts per million (ppm). This is apart from in fruit, which has a limit of 0.01ppm.
Residues of up to 30ppm are allowed in some imported foods, such as cereal grains.
But the use of glyphosate remains hotly contested by campaigners and some scientists, because of health and environmental concerns.
Recently, the EPA called for information about the manufacture, importation, and patterns of use of the weedkiller in this country, ahead a review of the classification of glyphosate in Europe.
The EPA said that would ensure it was better prepared to assess the findings of the review, due to be released in mid-2022, by the European Chemicals Agency (ECHA) and the EFSA.
‘‘We want to understand whether products containing glyphosate may be damaging the environment or human health, despite the clear rules in place,’’ said Dr Chris Hill, EPA general manager hazardous substances and new organisms.
‘‘We also want to know about the economic benefits of glyphosate’s use, and any potential alternatives.’’
Why do local authorities use glyphosate?
Many councils use glyphosate to kill weeds in public spaces, including parks and playgrounds.
But they say they also use the chemical to maintain safety in road transport corridors, to protect assets like kerbsides and help with ecological restoration projects.
Some local boards choose not to use it at all.
Auckland Council and Christchurch City Council last year backed away from proposals to expand their glyphosate use.
Auckland Council did so after alternative methods for killing weeds, such as hot water, plant-based herbicide and removal by hand, were found not to be as expensive as stated.
Christchurch City Council acted after opponents branded the plan ‘‘short-sighted’’, and environmental campaigners called for a reduction in spraying as a way of getting rid of weeds.
Wellington City Council said it currently did not have ‘‘suitable alternatives’’ to glyphosate, which it used to protect and maintain infrastructural assets, ensure public safety, and protect the natural environment from invasive or difficult-to-control weed species.
Nelson City Council said it was prioritising a review on its use of glyphosate, over ecological, economic and health concerns from some in the community.
The council – recently targeted by Extinction Rebellion protesters for its use of the weedkiller – said 49 per cent of the 441 litres of glyphosate concentrate it used in 2019 was on its parks.
Seventeen per cent was used in roadside vegetation, 28 per cent on forestry, and 6 per cent on ecological restoration/environmental weed control activities.
The council said it sought to minimise glyphosate use in parks through mulching, and techniques including hand-weeding.
Is glyphosate harming humans and the environment?
That is the multibillion-dollar question. German conglomerate Bayer AG, which bought Monsanto in 2018, has committed more than US$10 billion to settle a flood of US lawsuits alleging Roundup caused cancer.
The company says decades of
studies show glyphosate is safe for human use.
In New Zealand, toxicologist Dr Belinda Cridge, from the Institute of Environmental Science and Research, says all chemicals pose risks.
While the IARC found glyphosate had the potential to cause cancer, it did not assess the chances of that occurring.
Glyphosate affects soil composition, but poses a very low risk to human and animal health as it breaks down ‘‘reasonably quickly’’, based on factors including soil chemistry and rainfall, Cridge says.
She believes there is no evidence that it is unsafe for people to use if applied correctly, using protective gear while spraying, and not spraying in high winds.
But the Soil and Health Association of New Zealand says evidence that glyphosate has the potential to cause harm to people
‘‘I do not deny glyophosate is a toxin. But a little bit of negative achieves a hell of a lot of positive.’’
should be enough for it to be banned in public places and around waterways.
Its glyphosate spokesperson, Jodie Bruning, says research overseas shows glyphosate can last in soils for months.
Countries in Europe and elsewhere are moving away from using glyphosate where the public could be exposed, and New Zealand should do the same on a ‘‘precautionary principle’’.
She says the EPA never conducted a risk assessment of glyphosate to understand how it worked in the New Zealand environment. ‘‘Local councils need to take the initiative . . . because they are responsible for protecting public health.’’
Why do ecologists use glyphosate?
Ian Price, from Forest & Bird, has been using glyphosate to help restore native forests in the Nelson region for more than 30 years.
He sprays the grass with it before planting, and uses glyphosate ‘‘intensively’’ for 12 months, until the trees start shading the grass.
Before he started using glyphosate, he would lose 60 per cent of native plantings, he says. That compares to 2-3 per cent now.
‘‘I do not deny glyophosate is a toxin. But a little bit of negative achieves a hell of a lot of positive.’’
Controlling the grass early means native forests can establish quickly, providing an environment that fosters biodiversity.
With 14,500 trees to plant this year, it is practical and cost-effective to use glyphosate, he says.
Should glyphosate be reclassified?
University of Canterbury toxicology professor Ian Shaw says glyphosate should be categorised as hazardous until proven otherwise.
Having recently reviewed the gamut of scientific papers on glyphosate, he says we don’t know enough about its long-term effects.
When glyphosate was licensed in the 1970s, it was seen as the ‘‘holy grail of pesticides’’, with no effects on humans and animals.
‘‘One of the important environmental aspects of it was that it was quickly removed from the environment. We now know that really isn’t true.’’
The risks to people from single spraying or exposure to glyphosate are very low, he says.
But the chemical is constantly leaching into the environment, binding to soils and sediment in rivers and streams, and breaking down to a compound about which we knew very little.
‘‘We don’t have enough data about glyphosate’s long-term effects to rule out that it might be a carcinogen, and to rule out that it might be affecting ecosystems in a long-term context.
‘‘We’ve got to . . . do a proper study that gives a definitive result, rather than lots of bits and pieces from around the world, that confuse the picture.’’
He says there are ‘‘good reasons’’ to use glyphosate in a farm setting, and as a ‘‘one-off’’ for planting natives. But whether councils should use glyphosate routinely to control weeds at the side of roads is ‘‘highly questionable’’.
Is glyphosate killing bees?
Environmental campaign group Extinction Rebellion says 2018 research found glyphosate disturbs the gut bacteria of bees, making them more susceptible to parasites, and could disorient the pollinators, disrupting hive activity.
But Kerry Harrington, associate professor in weed science at Massey University, says the study, released through the Proceedings of the National Academy of Sciences of the USA, does not show a strong link between normal glyphosate use and the health of bees.
‘‘It appears there are many other things that are just as likely to affect bees, and the importance of glyphosate compared with many of these other environmental factors is still very much unknown.’’
Using hot water or steam to kill weeds instead of glyphosate requires more frequent treatment, more use of fossil-fuels and emissions of carbon dioxide, and would lead to a buildup of weed species that were partially tolerant of heat, he says.
Alternative herbicides are either more expensive, less effective or have safety issues.