Weed Control Q&A

Is glyphosate dangerous to people?

We rely on Chemical Regulations Division of the UK Health and Safety Executive to test herbicides and decide if they are safe or not.

Glyphosate-based herbicides are currently fully licenced as being safe for use in the public realm and the product we use carries no warning labels, which means even our weed control contractors are not legally required to wear protective equipment such as masks or gloves when applying it.

But hang on, I'm sure I've heard that glyphosate has been declared carcinogenic. That doesn't sound safe.

You're probably thinking about the decision taken in 2015 by the International Agency for Research on Cancer (part of the World Health Organisation) to classify glyphosate as "probably carcinogenic."

To put this decision into context, the IARC also lists eating red meat, working as a hairdresser, working night shifts, and drinking very hot beverages in the same category as glyphosate.

Since 2015, glyphosate has been reviewed by 19 other agencies, including the European Chemicals Agency, the European Food Safety Authority, the European Commission, the Swiss Federal Food Safety and Veterinary Office, the Australian Pesticides and Veterinary Medicines Authority, the New Zealand Environmental Protection Agency, and three different branches of the World Health Organisation. All these reviews have rejected the view that glyphosate is "probably carcinogenic."

As we said earlier, we rely on decisions taken by the Chemicals Regulation Division of the UK Health and Safety Executive to determine what is, and what isn't safe to use, and they have recently decided to extend approval for glyphosate to be used in the public realm for a further three years.

You can find out more about the CRD's view on glyphosate here:https://www.hse.gov.uk/pesticides/using-pesticides/general/glyphosate-faqs.htm

Okay, but I thought you declared a nature emergency, isn't glyphosate bad for pollinators?

According to the Final Project Report prepared independently by Dr Dan Jones the evidence on this is blurred, even for the scientific community, and mainly relates to reduction in beneficial gut flora, and reductions in mobility - but this is something we're very conscious of. It's one of the reasons we have committed to reviewing the use of glyphosate in all of our parks, with a view to further reducing our usage.

There is more detail on the evidence around the impact of glyphosate on pollinators in section 6.4 of the Final Project Report, which notes that much of the existing research looks at glyphosate as applied at an agricultural scale, where herbicide application can involve blanket spraying of different herbicides, several times throughout the year. The scale of herbicide use in Cardiff is significantly smaller, with spot treatments being applied directly to growing plants in vastly lower quantities - approximately 0.12 grams per square metre of pavement every year (one gram being the equivalent by volume of a quarter of a teaspoon),

Ultimately all methods of weed control can have unintended impacts on pollinators and other invertebrates, for example hot foam requires the application of very high volumes of boiling water, which could kill any wildlife it came into contact with. Even the mechanical removal of weeds using metal brushes or tools has the potential to kill wildlife.

So, what was the problem with the alternative methods of weed control you trialled?

In short, the evidence in the trial suggests they aren't as sustainable in the real-world as glyphosate, or as effective.

Glyphosate was by far the most efficient and effective method of weed control trialled - during the trial only four complaints about weeds were received in the area where glyphosate was being used, compared to 22 for acetic acid, and 29 for hot foam.

Glyphosate was also by the far the most expensive product. Based on operational experience and outcomes from the trial it is estimated that using acetic acid on pavement surfaces would result in a 667% increase in costs, when compared to glyphosate, and a 1000% increase if hot foam was used.

In addition, once you look at the full life-cycle of the product, factoring in things like the amount of fuel and water used, it was also the least damaging to the environment - in fact, glyphosate had the lowest impact in all but two of the 18 different environmental impact categories looked at in the independent research.

The 18 categories looked at were: Global Warming, Stratospheric Ozone Depletion, Ionizing Radiation, Ozone Formation (Human Health), Fine Particulate Matter Formation, Ozone Formation (Terrestrial Ecosystems), Terrestrial Acidification, Freshwater Eutrophication, Marine Eutrophication, Terrestrial Ecotoxicity, Freshwater Ecotoxicity, Marine Ecotoxicity, Human Carcinogenic Toxicity, Human Non-carcinogenic Toxicity, Land Use, Mineral Resource Scarcity, Fossil Resource Scarcity, Water Consumption.

As an example, treatment with hot foam required 629.64 litres of water per kilometre - 62 times more water than glyphosate, which required 13 litres per kilometre.

Application of glyphosate required 0.18 litres of diesel per kilometre, acetic acid required 0.19 litres. Hot foam used 12.33 litres of diesel plus 2.13 litres of petrol per kilometre treated - 63 times more diesel and 100% more petrol than required for glyphosate.

If glyphosate is sustainable, why are you still planning to reduce the amount you use?

All methods of weed control have an environmental impact. Although the research shows that glyphosate is the most sustainable option currently available on the market, it still has an environmental impact - therefore, the less we can use while still keeping pavements clear of trip-hazards, the better.

Wouldn't it be better not to use any herbicide at all though?

For nature, it would - after all, weed control is essentially killing plants. But cities need to work for the people who live in them as well. We have a duty of care to keep pavements clear, and free from the trip hazards caused by weeds - imagine trying push a pushchair along a pavement that was covered in weeds, or how difficult it might be for a wheelchair user, or an elderly resident. If left untreated, then the situation would get worse and worse every year.

But why not use mechanical methods, such as metal brushes and tools, or even flames?

Well, both of those would be great if the only concern was using less herbicide, but there are significant issues with both these methods.

Use of flames poses a significant health and safety risk and is currently not regulated in the UK - you couldn't, for example, use flames in proximity to parked cars or any other flammable materials, such as leaves. Because flames only kill the weed above ground (as opposed to glyphosate, which kills the entire weed) more treatment applications would be required, increasing the energy costs of creating flames. Flames would also kill wildlife on contact.

Metal brushes and tools are very carbon intensive, and very costly, to produce. While we use these methods in certain situations as part of our integrated approach to weed control there are limits to their practicality on a large scale as they require many more treatments in order to be effective, meaning higher labour costs and energy/carbon requirements. It's important to remember that this machinery can also kill wildlife on contact.

How much glyphosate do you use at the moment?

In 2021 we used 3,500 litres. Annual figures naturally vary from year to year, depending on weather conditions, however this is a reduction of around 80% in comparison to previous application methods.

The amount we use is reduced by the use of WEED-IT (Weed Economical Eradication Detection - Intelligent Technology) machines. These computer-controlled herbicide application systems, specifically designed for use on hard surfaces, use sensors to detect the presence of weeds and trigger the accurate application of herbicide directly to the weeds.

Is there any way you can use even less glyphosate?

That's something we're going to be looking at, starting by reviewing where and how we apply glyphosate in our parks.

Every park is different but for example, we'll be looking to see if there is scope for us to reduce the amount we use along path edges, close to trees, or near areas we maintain on a ‘one-cut' mowing regime or that are planted with wildflowers.

Does this mean you'll always use glyphosate?

No, not necessarily. At the moment there aren't many alternatives available - and the independent research that's just been conducted shows that they're not as sustainable as glyphosate. As and when new products or techniques become available, we will consider using them, if they prove to be more sustainable than glyphosate.

What do the companies who produce the products you trialled have to say about the results?

We contacted the manufactures of the two alternative products we trialled ahead of the final report being published.

The response from the manufacturers of the acetic acid product that was trialled related to technical detail around the concentration of the product. A number of minor changes were made to the final report to clarify that the product they produce is diluted with water to lower the concentration levels and therefore minimise any potential risks to people and wildlife.

The response from the manufacturers of the hot foam product trialled stated that they felt the figure of 4.89 hours of labour to treat one kilometre was inaccurate and that the task could be carried out with one operator per unit rather than the three used in the trial. They also highlighted their recent introduction of a new hybrid system that uses battery power to help reduce emissions.

Did the comments from the companies change your views on which products to use?

No, they did not.

Based on the overall environmental and economic performance of the products during the trial we believe that even taking into account the issues raised, our existing responsible glyphosate-based approach to weed control would still be, to quote the results of the report "the most effective and sustainable method of weed control currently available in the UK."

The full results of the alternative weed control trial are available here: https://cardiff.moderngov.co.uk/documents/s65772/Item%203%20-%20Appendix%20A.pdf?LLL=0