Australasian Science Magazine

By AusSMC

A Melbourne gardener has launched legal action in the first Australian case to link cancer with glyphosate, the active ingredient in the weedkiller Roundup. While glyphosate is considered “probably carcinogenic”, some experts dispute this conclusion.

“Glyphosate is considered by the International Agency for Research on Cancer [IARC] to be probably carcinogenic to humans (https://bit.ly/2NlI6oZ). Here are the relevant conclusions:

6.1 Cancer in humans

There is limited evidence in humans for the carcinogenicity of glyphosate. A positive association has been observed for non-Hodgkin lymphoma.

6.2 Cancer in experimental animals

There is sufficient evidence in experimental animals for the carcinogenicity of glyphosate.

6.3 Overall evaluation

Glyphosate is probably carcinogenic to humans (Group 2A).

6.4 Rationale

In making this overall evaluation, the Working Group noted that the mechanistic and other relevant data support the classification of glyphosate in Group 2A.

In addition to limited evidence for the carcinogenicity of glyphosate in humans and sufficient evidence for the carcinogenicity of glyphosate in experimental animals, there is strong evidence that glyphosate can operate through two key characteristics of known human carcinogens, and that these can be operative in humans. Specifically:

• There is strong evidence that exposure to glyphosate or glyphosate-based formulations is genotoxic based on studies in humans in vitro and studies in experimental animals. One study in several communities in individuals exposed to glyphosate-based formu- lations also found chromosomal damage in blood cells; in this study, markers of chromosomal damage (micronucleus formation) were significantly greater after exposure than before exposure in the same individuals.
• There is strong evidence that glyphosate, glyphosate-based formulations, and aminomethylphosphonic acid can act to induce oxidative stress based on studies in experimental animals, and in studies in humans in vitro. This mechanism has been challenged experimentally by administering antioxidants, which abrogated the effects of glyphosate on oxidative stress. Studies in aquatic species provide additional evidence for glyphosate-induced oxidative stress.

Note in the above that there is strong experimental evidence that glyphosate can cause cancer. There is also epidemiological evidence that it causes non-Hodgkin lymphoma (NHL), but this is not conclusive. Here is the relevant summary:

In summary, case–control studies in the USA, Canada, and Sweden reported increased risks for NHL associated with exposure to glyphosate. The increased risk persisted in the studies that adjusted for exposure to other pesticides. The AHS cohort did not show an excess of NHL. The Working Group noted that there were excesses reported for multiple myeloma in three studies; however, they did not weight this evidence as strongly as that of NHL because of the possibility that chance could not be excluded; none of the risk estimates were statistically significant nor were they adjusted for other pesticide exposures.

The AHS is the Agricultural Health Study, a large cohort study of workers in agriculture in the USA.”

Em/Prof Bruce Armstrong is Professor of Public Health at The University of Sydney’s School of Public Health.

“The International Agency for Research on Cancer made a bad mistake in claiming glyphosate was a probable cause of cancer. There is no convincing evidence for this, and much evidence gathered over 40 years about it as the safest herbicide known. Any replacement will be more likely to be damaging to human health.

It is unfortunate farmers are so reliant on glyphosate, and that alternatives as good aren’t available. But... finding a replacement as good is very unlikely. The precise specificity for affecting plants only by a chemical inherently so safe to animals is unlikely to be repeated.

I sincerely regret that the law is being used so badly in this case.”

Prof Tim Driscoll is an expert in cancer, workplace injury and disease at The University of Sydney’s School of Public Health.

“While two related people developing cancer at the same time is clearly worthy of investigation and research, we must be careful not to draw a causal link between their disease and glyphosate. It is important to remember that every year there are many hundreds of thousands of people who use the pesticide, or been exposed to it, who do not develop cancer.”

A/Prof Nial Wheate is an expert on cancer drugs and pharmaceuticals at The University of Sydney.

“The overwhelming opinion of experts is that glyphosate is safe. People forget ‘the dose maketh the poison’.

The scary data sheets that come with herbicides are for the concentrated compound, plus all the chemicals needed to dissolve it, plus the detergents needed to allow the chemical to penetrate the leaf – the concentrate is a toxic cocktail to be sure. However, the concentration at which what’s in the bottle is applied is usually 1000 times less, or even more dilute than that. What might remain behind days or weeks after spraying might be many orders of magnitude more dilute than what it was applied at.

Our exposure to toxins is a constant – some exposure is more noticeable than others. One of our favourite drugs, alcohol, is quite toxic and a known carcinogen yet we pour it down our throats with vigour every weekend. It is considered a carcinogen by Cancer Australia as well as the IARC, who ruled that for ethanol there was “sufficient evidence (highest IARC classification of carcinogenicity)” for it causing cancer of the oral cavity, pharynx, larynx, oesophagus, colorectum, liver (hepatocellular carcinoma) and female breast.

I am disappointed to think Australia might go down the same road as the hyper-litigious USA.”

Dr Joshua Mylne is an Australian Research Council Future Fellow appointed jointly to the School of Chemistry and Biochemistry and The ARC Centre of Excellence in Plant Energy Biology at The University of Western Australia.