Written by Peter Griffin
OPINION: The NZ Environmental Protection Authority made the right call last week to leave glyphosate off a list of chemicals it will reassess to determine their risk to people and the environment.
In doing so, it resisted political pressure to put use of glyphosate-based weedkiller like Roundup in the spotlight.
Associate Environment Minister and Green MP Eugenie Sage had wanted the EPA to consider classifying glyphosate as a hazardous chemical.
There's a movement, particularly in Europe, to have glyphosate banned.
But those efforts are driven as much by hatred of Monsanto, the US company that produces Roundup as well as genetically modified seeds, as by suggestions glyphosate causes cancer in humans.
The evidence for the latter is weak, according to large scale studies, and regulatory agencies around the world that have allowed glyphosate's continued use in gardens and on farms.
A decision in 2015 by the World Health Organisation's International Agency for Research on Cancer to classify it as "probably carcinogenic to humans" gave opponents ammunition.
The IARC finding was cited in the case of 46-year-old Dewayne Johnson, who in August won a landmark US$289 million court victory against Monsanto, which is now owned by German chemical company Bayer.
Johnson claimed that, as a school groundskeeper in San Francisco, exposure to Roundup was responsible for the Non-Hodgkin lymphoma that is killing him. As I wrote this, a judge in California was considering overturning that jury verdict.
Did IARC got the science wrong? No.
It was widely criticised for excluding important information, but the trouble stems from a misunderstanding of IARC's role.
The agency reviews scientific literature to determine "hazard" – whether a substance has the potential to cause harm.
More relevant is "risk", the likelihood that the hazard will actually cause us harm.
Red meat is "probably carcinogenic" as well according to IARC, but in reality it depends on how much of it we consume, how it is cooked and numerous other factors.
IARC leaves regulators to determine risk and in 2016 the EPA found that "based on a weight of evidence", glyphosate was unlikely to cause cancer when used as recommended.
A reassessment would change nothing, but drag it firmly onto the battlefield to join 1080, water fluoridation and genetic modification in being demonised for non-scientific reasons.