Should we continue using glyphosate (Roundup)?

Sunday 14 April, 7 pm.
Location: TBC.
Main discussion topic: Should we continue using glyphosate (Roundup)?
Logical fallacy: Confirmation Bias – when did you last fall victim to this fallacy?

For this meeting, I suggest we use our Critical Thinking skills to create an argument in standard form from our Glyphosate discussion:

P1 – Premise One
P2 – Premise Two
P3 – Premise Three
(continue for however many premises are required)
C Conclusion


Glyphosate is a broad-spectrum systemic herbicide and crop desiccant.

It was discovered to be an herbicide by Monsanto chemist John E. Franz in 1970. Monsanto brought it to market for agricultural use in 1974 under the trade name Roundup. Farmers quickly adopted glyphosate for agricultural weed control, especially after Monsanto introduced glyphosate-resistant Roundup Ready crops, enabling farmers to kill weeds without killing their crops. In 2007, glyphosate was the most used herbicide in the United States’ agricultural sector and the second-most used (after 2,4-D) in home and garden.

Glyphosate is absorbed through foliage, and minimally through roots, and transported to growing points. It inhibits a plant enzyme involved in the synthesis of three aromatic amino acids: tyrosine, tryptophan, and phenylalanine. It is therefore effective only on actively growing plants and is not effective as a pre-emergence herbicide.

In March 2015, the World Health Organization’s International Agency for Research on Cancer classified glyphosate as “probably carcinogenic in humans” (category 2A) based on epidemiological studies, animal studies, and in vitro studies.

In contrast, the European Food Safety Authority concluded in November 2015 that “the substance is unlikely to be genotoxic (i.e. damaging to DNA) or to pose a carcinogenic threat to humans”, later clarifying that while carcinogenic glyphosate-containing formulations may exist, studies “that look solely at the active substance glyphosate do not show this effect.”

The WHO and FAO Joint committee on pesticide residues issued a report in 2016 stating the use of glyphosate formulations does not necessarily constitute a health risk, and giving admissible daily maximum intake limits (one milligram/kg of body weight per day) for chronic toxicity.

In June 2018, Dewayne Johnson, a 46-year-old former California school groundskeeper who is dying of non-Hodgkin lymphoma, took Monsanto to trial, alleging that it has spent decades hiding the cancer-causing dangers of its Roundup herbicides. The jury awarded Johnson US$289 million in damages.


IARC Monograph on Glyphosate
NZ Herald – Roundup controversy and NZ
New Zealand Food Safety – Glyphosate
National Pesticide Information Centre (US)

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