Understanding the environmental impact of 6PPD-quinone in stormwater runoff

Understanding the environmental impact of 6PPD-quinone in stormwater runoff
Jun 27, 2023

The recent discovery of 6PPD-quinone as the leading cause of pre-spawn mortality for coho salmon has thrust the effects of urban stormwater on the Endangered Species Act (ESA) listed salmonids into the spotlight. It has also triggered federal agencies, such as the National Marine Fisheries Service (NMFS), to reconsider how effects associated with stormwater runoff are quantified and categorized.

We talked with Forrest Carpenter, ICF fisheries biologist, about the discovery of 6PPD-quinone, its risk to aquatic wildlife and the environment, and the regulatory response. 

ICF: What is 6PPD-quinone?

Forrest Carpenter: 6PPD-quinone is a chemical antioxidant that’s used in vehicle tires to prevent tire degradation when exposed to oxygen. Every time a vehicle drives on roadways, small bits of tire treads break off and accumulate on road surfaces. When it rains—which it does a lot in the Pacific Northwest—these bits of tire are washed into stormwater drains and eventually reach rivers and streams, posing a risk to aquatic organisms like salmon, steelhead, and other fish and marine organisms.

ICF: What are the impacts of 6PPD-quinone on wildlife and the environment?

Forrest Carpenter: 6PPD has been linked to pre-spawn mortality of Puget Sound coho salmon. Puget Sound is a highly urbanized area with many streams and rivers supporting salmon and steelhead. Researchers began looking into what was causing widespread coho mortality and determined that stormwater runoff from the urban environment was the cause.

It took many years for scientists to nail down precisely what chemical was causing such rapid mortality in coho salmon. In 2020, a pivotal paper from the University of Washington identified the compound as 6PPD, which changed the narrative around stormwater and its effects on salmon.

ICF: Are there any specific impacts on wildlife or the environment?

Forrest Carpenter: The focus of research in the Pacific Northwest has primarily been on the effects of 6PPD-quinone and stormwater on salmonids, such as coho, Chinook, and Sockeye salmon. While research on the specific impacts to other fish and wildlife is limited, different fish species and wildlife could be affected. The bioaccumulation of toxic chemicals up the food chain, such as in fish consumed by birds or mammals, can have wide-ranging effects.

For example, southern resident killer whales have been in the news a lot recently because of dwindling numbers. They're an ESA-protected species, and being at the top of the food chain, they are at risk of accumulating high loads of environmental toxins—including 6PPD—within their tissues. 

ICF: Are there any ongoing efforts to address the issue of 6PPD-quinone in the stormwater runoff?

Forrest Carpenter: There are ongoing efforts to identify effective methods of removing 6PPD-quinone from stormwater runoff. Various research groups, particularly in the Pacific Northwest, are studying the toxic effects of stormwater and exploring treatment options. These efforts involve universities like the University of Washington and Washington State University as well as government agencies like the Washington Department of Ecology and the Environmental Protection Agency (EPA).

Treatment options, including green stormwater infrastructure like treatment ponds and bioswales, are being explored. The NMFS’s Northwest Fisheries Science Center is also researching additional aspects of stormwater toxicity on Pacific Salmon and other listed fish and aquatic species. 

ICF: Are regulators going to pursue permitting?

Forrest Carpenter: No one has developed a method to remove 100% of toxic chemicals in stormwater before discharging into the aquatic environment. Green stormwater infrastructure can remove a very high percentage of harmful chemicals before discharging into streams and rivers, but the scale of the problem makes it challenging to completely prevent all of the substances from running into the aquatic system. Federal and state regulators are relying on research to inform their policies and to move the needle toward minimizing the impacts of stormwater runoff on our endangered species. That's a big focus for federal regulators.

State regulators have specific mandates as well and are working to leverage the best available science to implement the best treatment methods for new projects. There are implications from a human standpoint, as well. These toxic chemicals are in waterways that people use for recreation. How does that exposure affect humans? We eat salmon and other fish, and what is the consequence of having those chemicals in the food we eat?

ICF: What is our role in addressing the issue of 6PPD-quinone in stormwater runoff?

Forrest Carpenter: Our experts have extensive stormwater science experience, handling ESA consultations and analyzing project effects on various ESA-listed species including salmon, steelhead, bull trout, sturgeon, and rockfish. ICF helps clients navigate the federal and state permitting landscape when a project has a stormwater nexus. We work with with agencies to understand permit requirements so we can advise our clients on how to best submit project permit applications.

Permitting processes can take longer, particularly when a project impacts stormwater runoff. More impervious surfaces will contribute to stormwater runoff, which requires a more involved permit process because of the adverse impacts to species. We also help clients navigate that process and advise them on how best to design their projects to gain agency support and the appropriate permits. 

Addressing the threat of 6PPD-quinone

The discovery of 6PPD-quinone as the leading cause of pre-spawn mortality in coho salmon brings the detrimental effects of stormwater runoff on endangered salmonids to the forefront of environmental concerns. While efforts to address the issue of 6PPD-quinone in stormwater runoff continue, regulators focus on minimizing the impacts of stormwater runoff on endangered species. It’s important to stay proactive during project planning when ESA-listed salmonids may be affected. 

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