Council urged to rethink use of controversial herbicide near waterways

Tuesday, 4 October 2022

Christchurch’s Travis Wetlands are a biodiversity hotspot in the city. (File photo)

A toxicologist says Christchurch’s council should reconsider spraying a controversial herbicide near waterways, after it was revealed it’s still being used at popular wetland parks.

Glyphosate – one of the world’s most common weedkillers – was classified in 2015 as being 'probably carcinogenic to humans' by the International Agency for Research on Cancer.

In 2016, the Christchurch City Council resolved to use the chemical only on sites closed to the public or places where no other method was practical.

It considered re-upping its glyphosate use in 2020 to save money, but backed down after two-thirds of public submissions on its annual plan opposed it.

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Extinction Rebellion's Torfida Wainwright pleads with the Christchurch City Council to stop using all herbicides to prevent the killing of insects.

Local mum Genevieve Robinson – who is also running for the regional council, Environment Canterbury – recently attended a public planting day at Travis Wetlands with her son, and was told by a ranger that glyphosate was used there.

Council head of parks Andrew Rutledge confirmed staff used it at some wetland restoration sites, as it was the only chemical they were permitted to use for plantings near waterways.

It was also used for weed control in those areas “if no other alternatives are available”.

“It is considered the most appropriate herbicide for the preparation of wetland planting sites adjacent to waterways because it is non-residual.”

University of Canterbury toxicology professor Ian Shaw says the council should reconsider using glyphosate near waterways. (File photo)

New Zealand’s Environmental Protection Authority advises against spraying glyphosate “close to water, such as streams, rivers, lakes or ponds”.

Glyphosate was first approved for use in the 1970s, “but we’ve learned a lot about it since then”, University of Canterbury toxicologist Ian Shaw said.

Glyphosate was maybe the “least toxic” herbicide to use near waterways, but he questioned whether it had to be used at all.

“It’s for cosmetic reasons most often.”

Glyphosate is an ingredient in commercially-available weed killer Roundup. (File photo)

Glyphosate should be used near waterways only to control things that could be putting them at risk, he said.

Tests at the time showed it disappeared from soil quickly, but Shaw said we now knew it was not just breaking down.

“A good portion of it binds to the soil … there is the chance for it to be released further down the line.”

Shaw said not much was known about how glyphosate behaved in waterways, although it definitely broke down in water to some extent.

“[But] we don’t know what proportion of it is breaking down.”

What studies did show was that it could affect tiny animals living in waterways – like water fleas – at much lower doses than needed to damage aquatic plants.

“There’s no question it will have an impact on creatures around the same size.”

Smaller animals were at the bottom of much larger food chains, Shaw said, and if they disappeared it could mean little fish, then bigger fish and birds lost an important food source.

Dead bees attend Christchurch City Council's draft annual plan submission hearings to protest against a council plan to increase glyphosate usage in 2020.

There was good news for the public.

“We do have to keep glyphosate in perspective, it’s not lethal.

“If you’ve got people doing these good things – like planting days out in the wetlands – it’s highly unlikely they’d be at risk.”

Robinson said the council’s 2016 resolution specifically stated glyphosate was only to be used in places not frequented by the public, or hard to get to.

“Travis Wetland is not one of those places.

“When we’ve declared this as a council, it shouldn’t be used willy-nilly like that. [The council] should be showing leadership.”

Robinson wanted places where glyphosate was used to be clearly labelled.

Rutledge said those areas were closed to the public during application, and opened when it was safe to re-enter.

It had also been used this year at Halswell Quarry, the Port Hills, and in the red zone at Chimera Cres – at the request of a volunteer planting group.

“Only when there are no other means practical and only for the purpose of pest plant control..”

Rutledge said the council was still committed to its 2016 resolution, and considered its current level of use safe for the public.

*CORRECTION: An earlier version of this story incorrectly described glyphosate as a pesticide. It is a herbicide. (Amended 9.12am, October 11, 2022)