Monsanto loses glyphosate cancer case – expert reaction

A review of the safety of Roundup in New Zealand is among the likely consequences of the court case in the US which resulted in Monsanto being ordered to pay US$289 million (NZ$439 million) to a former school groundskeeper after a jury found it contributed to the man’s terminal cancer.

Dewayne Johnson claimed Monsanto’s popular Roundup weed killer was linked to his disease.

After three days of deliberations, a San Francisco jury awarded him US$250 million (NZ$380 million) in punitive damages and around US$39 million (NZ$59 million) in compensatory damages.

The decision may pave the way for thousands of other cases alleging the glyphosate-based herbicide causes non-Hodgkin’s lymphoma.

Media headlines in this country included “Roundup case: Scientists caution against knee-jerk NZ ban” , but disagreement was reflected in the headline which said “NZ should ban Roundup weed killer – expert” .

The Environmental Protection Authority has ruled Roundup safe to use and the US ruling hadn’t changed that position but Associate Environment Minister Eugenie Sage said she would be asking the agency to consider adding it to its hazardous substance reassessment list in the light of the decision.

 The Science Media Centre has gathered these expert comments –  


Dr Belinda Cridge, Programme Leader and Lecturer in Toxicology, The University of Otago, comments:

“The court case is an interesting test case based on some relatively new evidence. In 2016, the International Agency for Research on Cancer (IARC) re-classfied glyphosate [the active ingredient in Roundup] as a ‘probable human carcinogen’ a decision based on an extensive review of available data including epidemiological [human] studies.

“However, the impact this finding is being debated widely, partly due to the involvement of large corporations and also because the IARC assesses a chemical’s carcinogenic potential but does not generally conduct a full risk assessment, judging where and how contact with the chemical may occur.

“These additional factors are important in determining the overall risk associated with the use of a chemical in various situations. For comparison and context the IARC has also classified red meat consumption as a probable carcinogen. This is based on good scientific evidence but highlights that understanding wider factors are critical to determining full risk. However, the underlying finding of the IARC stands, glyphosate may cause cancer under the right conditions and exposures.

“The case in the US cited that adjuvants [additives in the Roundup beyond the active glyphosate compound] may have had a synergistic effect to cause the cancer. Synergistic effects occur when two chemicals which are relatively benign separately, act together to make a small effect much worse.

“The toxicology of mixtures such as this is something that toxicologists are only just starting to really understand in any detail. It is very difficult to model and track all possible interactions. This means that there is a very real possibility that adjuvants in the Roundup mixture accelerated any carcinogenic effects but to the best of my knowledge this is hypothesised rather than proven. It is a very real possibility but has not been conclusively demonstrated using laboratory or epidemiological studies.

“The terms of the case are interesting as the plaintiff did not need to demonstrate conclusively that glyphosate caused the cancer, only that it was a plausible contributing factor. Also, Monsanto is unable to prove that glyphosate definitely did not cause the cancer. There is still no proof either way but the success of the prosecution will encourage others to seek remuneration using the IARC classification as evidence.

“Finally it is important to consider the whole picture. Roundup isn’t, and has never been, a safe panacea for all weed control. Scientists continue to learn more and more about this chemical and its effects. However, the alternative options aren’t very appealing and many are much much worse for both people and the environment.

“Roundup has been used extensively worldwide for a long time, it has a reasonably good safety record and has limited environmental effects – compared to the alternatives. Yes, improvement is needed but for farmers Roundup is one of the safer options currently available.

“My standard advice is for people to not use chemicals where they don’t need to (thinking of the home gardener, hand pulling weeds is tiresome but much safer than any chemical alternative), know what chemicals you are using and be rigorous about safety equipment. This applies to all the chemicals we use from home cleaners to industrial chemicals in the workplace to agrochemicals such as Roundup.”

No conflicts of interest declared.


Ian C Shaw FRSC, FRCPath, Professor of Toxicology, University of Canterbury, comments:

Is glyphosate a carcinogen?

“On March 20, 2014, the World Health Organisation’s (WHO) International Agency for Research on Cancer (IARC) classified glyphosate (the active component of Roundup) as Carcinogen 2b – possibly carcinogenic to humans. Based on the available animal data, cell culture studies and epidemiological data relating to human exposures, in my opinion this was a very reasonable conclusion.

“This classification led some countries to review their use of glyphosate, because the possibility of the chemical being a carcinogen in humans put into question the benefit of glyphosate (Roundup) when set against this considerably increased risk – prior to this, glyphosate was considered safe.

“NZ responded quite differently.

“The NZ EPA invited Dr Wayne Temple to consider and report on the IARC ruling and the data that was used for the IARC risk assessment. Dr Temple’s review concluded that glyphosate was unlikely to be a human carcinogen and unlikely to be genotoxic (most carcinogens are genotoxic, i.e. damage genes). On the back of this deliberation, NZ decided not to reconsider the regulatory status of glyphosate-containing herbicides.

“Dr Temple seems not to have considered the possibility of non-genotoxic carcinogenesis (some chemicals that cause cancer do not directly alter genes) in his assessment of the results. This was particularly surprising because experiments have shown that glyphosate can interact with a cell receptor (estrogen receptor) that stimulates some cells to grow – this is the way some non-genotoxic carcinogens work. In view of this, and other aspects of Temple’s report, I found the NZ EPA’s decision lacked scientific rigour.

“The US court ruling was clearly based on an acceptance of the IARC classification and the evidence underpinning it. Remember though that the courts require a balance of probabilities (i.e. only 51 per cent) for a guilty verdict, while scientists usually require much greater statistical security.

“I do not think we should base our regulatory decisions on a US court case, but I do think that the evidence that glyphosate is possibly a carcinogen in humans is robust. I favour categorising glyphosate as hazardous and reassessing its regulatory status in NZ.”

No conflicts of interest.


Assoc Prof Brian Cox, cancer epidemiologist, University of Otago:

“In 2015, the IARC classified glyphosphate, a major ingredient of RoundUp, as a probable carcinogen (a possible cancer causing agent in their Group 2A category).

“That is, the IARC consider that there is limited evidence that glyphosphate may cause cancer, but the association with cancer may be due to other things.

“Herbicide use is seldom exposure to just one specific product and the dose, duration, type, and frequency of exposure is relevant to any potential risk.

“A jury in the USA has considered the limited evidence sufficient in an individual case to attribute a man’s non-Hodgkin lymphoma to his exposure to glyphosphate.

“A sudden reaction to one case in one US law court, that has not yet gone to the appeal court, is not an appropriate method of developing health policy in New Zealand.

“However, it is appropriate that New Zealand does keep watch on the overseas evidence about the risk of cancer from glyphosphate exposure and assess and balance of evidence of that risk and the views of users, the public and New Zealand industry.

“The IARC definition of Group 2A is: the agent is probably carcinogenic to humans. This category is used when there is limited evidence of carcinogenicity in humans and sufficient evidence of carcinogenicity in experimental animals. Limited evidence means that a positive association has been observed between exposure to the agent and cancer but that other explanations for the observations (called chance, bias, or confounding) could not be ruled out. This category is also used when there is limited evidence of carcinogenicity in humans and strong data on how the agent causes cancer.”

No conflicts of interest declared.


Dr Kerry Harrington, Senior Lecturer in Weed Science, Massey University:

“As I am a weed scientist and not a toxicologist, it is not appropriate for me to comment on the finer details of the toxicological debate over the safety of glyphosate. However, I can report that a number of recent reviews by toxicologists around the world have reiterated that glyphosate is a safe herbicide to use and does not cause cancer. These reviews take account of animal studies which directly measure whether a chemical causes cancer or not, which I understand were not taken into consideration by IARC when they claimed glyphosate does cause cancer.

“Even if it is as carcinogenic as claimed by IARC, this would appear to be in a category that is less risky than eating preserved meats, yet there is no outcry asking for these to be banned.

“It is a concern if decisions on the use of glyphosate in New Zealand hinge on the outcome of a court case in USA where a jury of ordinary members of the public had to decide about complex issues of toxicology.

“Glyphosate is one of our major weed control tools. Hopefully the calls for it to be banned will take into consideration the low risk of problems and the crucial importance of this herbicide for sustainable weed control worldwide.”

No conflicts of interest declared.

Author: Bob Edlin

Editor of AgScience Magazine and Editor of the AgScience Blog

Leave a Reply