Alexander
Kaurov, Te
Herenga Waka — Victoria University of
Wellington
Last month’s US Supreme
Court ruling
in favour of the makers of the weedkiller Roundup (formerly
Monsanto, now owned
by German pharmaceuticals group Bayer) upended
thousands of lawsuits based on the cancer
risk associated with the product’s active ingredient
glyphosate.
But
the ruling also highlights a longstanding controversy about
how the product’s use is approved, including in New
Zealand.
The US Environmental Protection Agency (EPA) has judged glyphosate
“not
likely” to cause cancer, while the World Health
Organization’s International Agency for Research on Cancer
(IARC) describes it
as “probably
carcinogenic to humans”.
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The two agencies
weigh the evidence differently. IARC uses only publicly
available studies and tests animal data for dose-response
trends, while the US EPA leans heavily on unpublished
studies commissioned by the manufacturer itself.
As a small country, New Zealand cannot itself
conduct full risk assessments of thousands of
chemicals in use, and leans on findings from bigger
agencies overseas.
In the case of glyphosate, New
Zealand’s approval process is based on several reviews
shaped by Monsanto. But I argue this is no longer tenable,
as one of them has now been retracted and two are under
investigation.
Compromised evidence in
regulatory decisions
Monsanto-produced evidence
has a questionable track record. Its early tests during the
1970s and ‘80s were conducted in contract laboratories
that have since been convicted
of fabricating data.
In 2017, litigation
forced Monsanto’s internal
documents to be unsealed. These exposed how the company
interacted with researchers who gave favourable assessments
and produced ghostwritten
reviews.
In this context, ghostwriting is the
practice of putting names of independent scientists on work
produced by employees of the company. It is explicitly
prohibited under the standards
of scientific
practice.
Faced with the divided evidence, New
Zealand’s Environmental Protection Authority (NZ EPA) commissioned its
own report in 2016. It concluded glyphosate is
“unlikely to be genotoxic or carcinogenic to humans”.
New Zealand scientists objected at the time. In
2018, six New Zealand public-health researchers, several of
whom have connections to IARC, challenged
the authority’s report.
They listed many
concerns, including reliance on unpublished industry studies
and ghostwriting. None of this moved the authority’s
position. In 2024, it again found no grounds to reassess the
use of glyphosate. A High Court challenge to this decision
was unsuccessful.
However,
the ground beneath this debate is shifting.
Three
key Monsanto reviews under scrutiny
Over the past
year, together with colleagues, I have traced how
Monsanto-influenced reviews shape
public discourse and regulation around the world.
We found they had been effective in their intended
purpose of convincing people and regulators of
glyphosate’s safety.
We called for them to be retracted
because
the first was
written by Monsanto and signed by outside academics. An internal
email describes the practice of writing the sections so
the named authors “would just edit & sign their
names”.
The journal retracted
this review in November 2025, noting Monsanto employees
“may have contributed […] without proper acknowledgement
as co-authors”, among other issues.
Another two
have recently come under
investigation.
One was
also shaped by Monsanto, with a company scientist who
helped write it deliberately
kept off the byline to make it look independent.
A recently
disclosed memo shows the US EPA’s own investigator
reached the same conclusion that the paper “hid
Monsanto’s role as an author”, but the agency kept
citing it.
Another review
published in 2015 discredited a study that had found
glyphosate caused a significant rise in malignant lymphoma
in mice, instead invoking a “viral
infection”. But subsequent independent
reanalysis found no evidence of this in the original
study.
Bayer continues to reject the ghostwriting
characterisation,
saying Monsanto’s involvement was appropriately cited in
the acknowledgments which thanked the company’s scientists
for “significant contributions”.
NZ should
reconsider glyphosate regulation
Institutional
trust varies significantly. US EPA emails from 2025 show
Bayer promising the agency “a
small thanks” for updating its glyphosate webpage.
By contrast, the judge in Australia’s
2024 Roundup class action warned that a company dealing
with regulators cannot be assumed to “play with a straight
bat,” and said the evidence gave him “concerns about
accepting anything from Monsanto at face value”. Yet the
2015 review was used by the applicant’s own
statistician.
New Zealand’s 2016 report also
leans on these three reviews. But now, in 2026, it is much
harder to treat them as legitimate evidence in an honest
scientific debate about glyphosate’s safety.
When
New Zealanders are told dietary exposure sits well under 1%
of the “acceptable
level”, they should keep in mind two things.
First, this level is based on industry-sponsored
studies. Second, an average hides how unevenly exposure
falls on sprayers, rural communities and people with
particular diets. These factors should be weighted in, but
New Zealand holds
almost no exposure data.
Glyphosate is only one
of 16 high-use pesticides in New Zealand flagged as
suspected carcinogens by at least one major
agency.
The costs of using them should be estimated
explicitly: an uptick in illnesses, strain on the healthcare
system, harm to the environment and lost quality of
life.
The intellectually honest process would be to
assess risks with broad scientific consultation and
acknowledgement of where evidence is compromised or plainly
missing.
For New Zealand to keep avoiding a
comprehensive reassessment of glyphosate is to make wilful
ignorance a matter of national policy.
Alexander
Kaurov, PhD Candidate in Science and Society, Te
Herenga Waka — Victoria University of
Wellington
This article is
republished from The
Conversation under a Creative Commons license. Read the
original
article.