Earlier this year, the Australian Federal Court closed submissions to a landmark lawsuit involving 800 people. They claimed the weed killer Roundup — and its active ingredient glyphosate — was carcinogenic and caused non-Hodgkin’s lymphoma. The judge ruled that there was insufficient evidence to say glyphosate was carcinogenic.
There have been similar cases in the US, and some states have introduced regulations on its use. Other countries have banned it altogether.
John E. Franz, a chemist working for Monsanto, discovered glyphosate as a herbicide in 1970. It has been sold as Roundup since 1974. The AVPMA (Australian Pesticides and Veterinary Medicines or Authority) defines glyphosate as a herbicide used to control weeds in agriculture, public and industrial areas, and in home gardens. It is broad-spectrum, meaning that it kills most plants. One of the benefits is that there is no need to till the land to fight weeds, therefore less soil erosion and better soil quality. Glyphosate is used in commercial sugarcane, grains, oil seeds and broadacre crops.
Some crops have been genetically engineered to be resistant to glyphosate. In the US, soybean, corn, cotton, canola, sugar beet and alfalfa. In Australia, canola is the only glyphosate-resistant GM crop. There are emerging species of glyphosate-resistant weeds.
Glyphosate’s mechanism of action involves disrupting a pathway, crucial for synthesising essential aromatic amino acids. It’s considered safe for people because animals, including humans, don’t possess this pathway. However, the diverse species of beneficial microbes in our biome does.
Research into glyphosate and possible acute or chronic toxicity or cancer risk is conflicted. The International Agency for Research on Cancer (IARC) classified glyphosate as “probably carcinogenic”, based on some studies suggesting an association between glyphosate exposure and non-Hodgkin’s lymphoma in humans. Pets are often exposed to glyphosate and may face similar risks.
There is limited research specifically linking glyphosate exposure to cancer in dogs or cats. A 2004 Scottish Terrier study linked herbicide exposure (mainly phenoxy herbicides like 2,4-D) to an increased risk of transitional cell carcinoma (bladder cancer) in these dogs. However, although this study shows potential risks with herbicide exposure, it is not specific to glyphosate.
Pets may be at risk of acute glyphosate toxicity if they touch or eat plants still wet from spray. Chronic exposure is via two main routes:
- Contact (walking on sprayed grass)
- Ingestion (foods containing it residues or licking off feet