In August 2018, PlantNetwork posted a summary of the debate concerning glyphosate. One year on, we thought an update was due as glyphosate has an important role in horticulture as well as wider food production and is likely to be in the news again as court cases proceed in the USA.
A summary is provided below but you might wish to access the full update here:
Glyphosate is the active agent in a range of herbicide products, collectively known as glyphosate-based herbicides (GBHs). GBHs are broad spectrum, post-emergent, non-selective (kills all vegetation), systemic herbicides and account for 25% of the global herbicide market. Its main use is in agriculture where it supports food production in arable, fruit and other crops but is also widely used in ornamental horticulture and in the domestic market. In the UK, there are 276 individual GBHs products authorised for use by amateurs and a further 170 products available to professional users. Professional users are considered to be holders of PA1 and application-specific qualifications which provide guidance on the safe use of pesticides to reduce environmental impact and prevent damage to human health.
Glyphosate, as the active ingredient, acts to inhibit plant growth, leading to treated plants starving to death. The enzyme on which it acts is only found in green plants and hence is much less biologically active in other organisms including mammals. Nevertheless, there is growing evidence of the wider environmental impact of glyphosate and GBHs, with adverse impacts reported for soil organisms, aquatic organisms, non-target plants and terrestrial animals including bees. In mammals, including humans, exposure to glyphosate/GBHs has been linked to immunosuppression, endocrine disruption, oxidative stress and genetic alterations leading to a number of studies identifying an association between glyphosate/GBHs and an increased likelihood of developing non-Hodgkin lymphoma (NHL).
The World Health Organisation’s International Agency for Research on Cancer (IARC) reviewed the evidence for the link between exposure to glyphosate/GBHs and NHL, determining that the evidence was strong enough to classify glyphosate as a Group 2A carcinogen: probably carcinogenic to humans (IARC, 2017). This classification has received considerable publicity, leading to a number of court cases in the USA which have found in favour of the plaintiffs against Bayer, the chemical manufacturer who bought the original developers of glyphosate, Monsanto. The evidence has been disputed by a number of organisations which have determined that glyphosate “is unlikely to pose a carcinogenic hazard to humans and the evidence does not support classification with regard to its carcinogenic potential according to Regulation (EC) No 1272/2008” (European Food Safety Authority, 2015). Particularly notable is the decision of the USEPA to describe glyphosate as “not likely to be carcinogenic to humans” (USEPA, 2016), directly opposing the IARC classification. The difference in attribution between IARC and USEPA is likely to be due to a number of different factors:
- While the USEPA largely considered glyphosate, IARC looked at studies including glyphosate, glyphosate metabolites and GBHs: there is growing evidence that other chemicals in GBHs have a greater toxic effect or increase the toxicity of glyphosate.
- Different targets were considered, with IARC considering more epidemiological studies including those with occupational exposure or particularly high exposure to GBHs (many of which would be unlikely under normal operating conditions); USEPA focused more on dietary exposure to glyphosate residues in food.
Despite these differences, there is still more work to be done to more fully evaluate the impact of glyphosate/GBH exposure to human health. In the meantime, horticulturists can take measures to reduce their exposure to GBHs through the use of personal protection equipment (PPE), ensuring full compliance with regulations and following the recommendations of manufacturers. Implementing integrated weed control measures to reduce reliance on GBHs will reduce occupational exposure as well as reducing the amounts entering the environment. The IARC classification for glyphosate/GBHs should also be put into perspective alongside other IARC classifications. For instance, consumption of processed meats and alcoholic beverages, and exposure to solar radiation are considered to be Group 1: carcinogenic to humans so arguably sunburn poses a greater threat to horticulturists then exposure to GBHs. For comparison, other IARC Group 2A carcinogens include consumption of red meat, emissions from high temperature frying, drinking very hot beverages and working as a hairdresser.
Suggestions for public gardens:
- Follow all manufacturers guidelines for use, storage and disposal of glyphosate including accurate recording all glyphosate use by volume and application type;
- Ensure that all PPE is effective and used properly to minimise operational exposure;
- Assess how much glyphosate is being used in your garden, where it is applied and for what reason – are current usage patterns strictly necessary?
- Develop a clear policy brief on the use of glyphosate in your garden defining when, where and how it is to be used including restrictions on use such as where alternative approaches exist and where bystander exposure might be an issue (gardens or areas with high visitor numbers/engagement). Implement this policy across your garden.
- Accept weedy areas – consider use of interpretation to explain to visitors why the area might not be pristine. Perhaps we need to be more accepting of the ‘messy garden’ look?
EFSA (2015). Conclusion on the peer review of the pesticide risk assessment of the active substance glyphosate. https://www.efsa.europa.eu/en/efsajournal/pub/4302. Accessed August 2019.
IARC (2017). Some Organophosphate Insecticides and Herbicides. IARC Monographs on the Evaluation of Carcinogenic Risks to Humans Volume 112. Available from: http://publications.iarc.fr/Book-And-Report-Series/Iarc-Monographs-On-The-Identification-Of-Carcinogenic-Hazards-To-Humans/Some-Organophosphate-Insecticides-And-Herbicides-2017. Accessed August 2019.
USEPA (2016). Glyphosate issue paper: evaluation of carcinogenic potential. https://www.epa.gov/sites/production/files/2016-09/documents/glyphosate_issue_paper_evaluation_of_carcincogenic_potential.pdf. Accessed August 2019.
There are lots of other resources available providing information on glyphosate, health issues associated with glyphosate and/or glyphosate-based herbicides. Well-balanced, peer-reviewed and objective interpretations and studies will be added here.
- BBC Radio 4’s More or Less: Behind the Statistics – Rounding up the weed killer cancer conundrum. First broadcast: 08 April 2019.
- Fiona E. Belbin, Gavin J. Hall, Amelia B. Jackson, Florence E. Schanschieff, George Archibald, Carl Formstone & Antony N. Dodd (2019). Plant circadian rhythms regulate the effectiveness of a glyphosate-based herbicide. Nature Communications 10, Article number: 3704. Listen to the lead author discuss the findings of the paper at Weeding the Gems.
Report prepared by and for PlantNetwork, August 2019