Herbicides Linked to Water Pollution Eyed for Public Land Use

The Biden administration is planning to control noxious weeds on federal land using seven new herbicides that scientists say can contaminate streams and groundwater and are harmful to aquatic life.

The plan and environmental review, announced last week, would allow seven additional herbicides to be used where noxious weeds are found on 245 million acres of federal land managed by the Bureau of Land Management across the West. It’s open for comment through June 5.

The agency hasn’t previously used the herbicides on its land and says it needs to use them to control invasive species because climate change is making some weeds less sensitive to herbicides that are currently approved for agency use on federal land.

“Herbicide efficiency is changing due to the impacts of climate change, including increasing temperatures, changes in precipitation, and elevated carbon dioxide,” the land bureau’s review says. “It is imperative to have multiple options for herbicides so that treatment can be as efficient as possible.”

But the review acknowledges that the new herbicides “have a wide range of mobility to and potential to enter surface and groundwater,” though they’re not included on the Environmental Protection Agency’s National Primary Drinking Water Regulation’s contaminant list, sparking potential downstream health concerns.

The herbicides the bureau is proposing to use include indaziflam, aminocyclopyrachlor, clethodim, fluazifop-P-butyl, flumioxazin, imazamox, and oryzalin.

The 21 herbicides the bureau currently uses include 2,4-D; dicamba; glyphosate; and others.

The EPA said last year that dicamba can harm animals, plants, and farm workers. Glyphosate, the main ingredient in Roundup, has been linked to cancer and is considered by the World Health Organization to damage DNA. A recent study, however, suggested weedkiller cancer risk comes from other ingredients.

A break along a road in White Pine County, Nev., was covered in cheatgrass and other invasive grasses in February 2020.

Photographer: Bobby Magill/Bloomberg Law

Better Than Dicamba?

The land bureau said it sprayed herbicides on a New York City-sized area of federal land in 2021, including spraying 31,000 acres with glyphosate and 2,800 acres with dicamba. The most common herbicide the bureau uses is imazapic, which is frequently used in natural areas to control weeds.

“One of the BLM’s highest priorities is to promote ecosystem health, and one of the greatest obstacles to achieving this goal is the rapid expansion of noxious and invasive weeds across public lands,” Brian St. George, acting BLM Assistant Director for Resources and Planning, said in a statement.

The new herbicides the bureau wants to use are an improvement over spraying glyphosate, dicamba, and other harmful chemicals to control weeds, but they’re still “powerful synthetic poisons” and their effects on surface and groundwater remain uncertain, said Robert Brakenridge, a senior research scientist and founder at the Dartmouth Flood Observatory at the University of Colorado, Boulder.

He said that the chemicals’ manufacturers don’t fully disclose the inert ingredients in the pesticides, and scientists are concerned that they could contain PFAS.

Brakenridge said that the overall toxicity of the chemicals the land bureau is proposing to use is still not fully known, but “there is clear ecological damage being committed.”

‘Very Toxic’

The bureau’s environmental review says that most of the herbicides the agency is proposing to use have been approved by the EPA and are mostly benign, but indaziflam has the potential to leach into groundwater and flow into streams where it can harm aquatic plants and algae.

Portland State University researchers in a 2021 study found indaziflam, considered “very toxic to aquatic life,” in bivalve tissue in five of eight coastal watersheds downstream of its use in Oregon forests.

All seven of the land bureau’s proposed herbicides could be toxic, said Allie Tissot, a PSU researcher and co-author of a related 2021 study.

“Based on published research as well as gaps in our current understanding of many of these herbicides, it is highly likely that these compounds will have adverse effects on aquatic ecosystems with potential for human health concerns,” Tissot said.

Oryzalin is also “highly toxic” to aquatic plants if it gets into streams, and it’s “moderately toxic” to fish, the land bureau said. The chemical has also been found to harm endangered species, the review says.

Some of the herbicides have been restricted in some states. Oregon restricted the use of aminocyclopyrachlor in 2019 because the state found that its use in national forests has killed old-growth trees.

Researchers have found that aminocyclopyrachlor remains in soils and can damage plants long after it’s applied, and it can flow into streams where it can harm aquatic life.

“Considering the effects of each of these herbicides, scientific data indicate that adding them to a management plan could cause considerable harm to aquatic ecosystems and a high likelihood of surface water contamination,” Tissot said, adding that the chemicals should only be used as a “last resort.”