In 2020, a stormwater contaminant called 6PPD was linked to "urban runoff mortality syndrome" in Coho salmon in the Puget Sound, Washington. 6PPD is an anti-wear chemical added to tires and other rubber-based products to increase the life of the tire and prevent degradation. When our tires wear down from friction with the road, they leave behind tiny particles, which can be washed from roads into aquatic ecosystems by rain. Photo: This bioswale was installed on the Cal Poly Humboldt campus along LK Wood Blvd. to intercept stormwater runoff from the Library Circle parking lot. These particles bring with them all the various chemicals and compounds added to tires, including 6PPD. As 6PPD is exposed to ozone in the air, it is transformed into 6PPD-quinone (6PPD-q), which is highly lethal to Coho salmon.According to scientists with the California State Water Resources Board, the LC50 (lethal concentration causing death in >50% of the test population) for Coho salmon exposed to 6PPD-q is one of the lowest ever reported for any chemical. This means that it takes a relatively small amount of 6PPD-q to kill Coho salmon, compared to other chemicals. So far, the research shows that certain species of fish are more sensitive to 6PPD-q than others. Chinook salmon has a much higher LC50, meaning that Chinook can withstand higher concentrations of 6PPD-q than Coho. Additional research has identified this chemical as acutely toxic to brook trout, lake trout, rainbow trout/steelhead, and coastal cutthroat trout. The Washington State Department of Ecology continues to lead the Pacific Northwest in understanding and responding to 6PPD and 6PPD-q.6PPD-q has been found to damage rodent liver and other organs, and to pass through the placenta to a fetal mouse. Monitoring in humans has measured 6PPD-q in human urine, blood serum, and cerebrospinal fluid, but research on toxicity to humans is ongoing.In June 2024, the US EPA released non-binding non-regulatory screening levels for 6PPD-q, which states and tribes can use in water quality protection programs to protect sensitive fish species. Additionally, the CA Department of Toxic Substances Control (via the Safe Consumer Products program) is working with tire manufacturers to identify alternatives to 6PPD, but so far they have focused on similar chemicals such as 7PPD, which may be just as toxic. The California Coastkeeper Alliance has called for the State Water Resources Board to establish stormwater discharge control measures to prevent 6PPD running off roads into fish bearing streams.Humboldt Waterkeeper has begun sampling stormwater runoff around Humboldt Bay in an effort to identify 6PPD hot spots like high-traffic parking lots and roads adjacent to salmon-bearing streams. As the science around 6PPD develops, we are refining our sampling strategy to align with the best available science. Right now, sampling for 6PPD is expensive and challenging. Concentrations of the contaminant in stormwater may peak an hour after a rain starts, so timing of sampling is critical. We hope to provide useful data to stormwater managers to prioritize locations for practices that will prevent or reduce the amount of 6PPD flowing into salmon-bearing streams.Currently, bioswales are the best available option. Researchers are currently determining the most effective materials to remove 6PPD and 6PPD-q from stormwater. A bioswale is essentially a vegetated stormwater drain; as stormwater percolates through the soil, mulch, compost, and plants pollutants are filtered out, and cleaner stormwater drains to nearby streams.
In 2020, a stormwater contaminant called 6PPD was linked to "urban runoff mortality syndrome" in Coho salmon in the Puget Sound, Washington. 6PPD is an anti-wear chemical added to tires and other rubber-based products to increase the life of the tire and prevent degradation. When our tires wear down from friction with the road, they leave behind tiny particles, which can be washed from roads into aquatic ecosystems by rain. Photo: This bioswale was installed on the Cal Poly Humboldt campus along LK Wood Blvd. to intercept stormwater runoff from the Library Circle parking lot. These particles bring with them all the various chemicals and compounds added to tires, including 6PPD. As 6PPD is exposed to ozone in the air, it is transformed into 6PPD-quinone (6PPD-q), which is highly lethal to Coho salmon.According to scientists with the California State Water Resources Board, the LC50 (lethal concentration causing death in >50% of the test population) for Coho salmon exposed to 6PPD-q is one of the lowest ever reported for any chemical. This means that it takes a relatively small amount of 6PPD-q to kill Coho salmon, compared to other chemicals. So far, the research shows that certain species of fish are more sensitive to 6PPD-q than others. Chinook salmon has a much higher LC50, meaning that Chinook can withstand higher concentrations of 6PPD-q than Coho. Additional research has identified this chemical as acutely toxic to brook trout, lake trout, rainbow trout/steelhead, and coastal cutthroat trout. The Washington State Department of Ecology continues to lead the Pacific Northwest in understanding and responding to 6PPD and 6PPD-q.6PPD-q has been found to damage rodent liver and other organs, and to pass through the placenta to a fetal mouse. Monitoring in humans has measured 6PPD-q in human urine, blood serum, and cerebrospinal fluid, but research on toxicity to humans is ongoing.In June 2024, the US EPA released non-binding non-regulatory screening levels for 6PPD-q, which states and tribes can use in water quality protection programs to protect sensitive fish species. Additionally, the CA Department of Toxic Substances Control (via the Safe Consumer Products program) is working with tire manufacturers to identify alternatives to 6PPD, but so far they have focused on similar chemicals such as 7PPD, which may be just as toxic. The California Coastkeeper Alliance has called for the State Water Resources Board to establish stormwater discharge control measures to prevent 6PPD running off roads into fish bearing streams.Humboldt Waterkeeper has begun sampling stormwater runoff around Humboldt Bay in an effort to identify 6PPD hot spots like high-traffic parking lots and roads adjacent to salmon-bearing streams. As the science around 6PPD develops, we are refining our sampling strategy to align with the best available science. Right now, sampling for 6PPD is expensive and challenging. Concentrations of the contaminant in stormwater may peak an hour after a rain starts, so timing of sampling is critical. We hope to provide useful data to stormwater managers to prioritize locations for practices that will prevent or reduce the amount of 6PPD flowing into salmon-bearing streams.Currently, bioswales are the best available option. Researchers are currently determining the most effective materials to remove 6PPD and 6PPD-q from stormwater. A bioswale is essentially a vegetated stormwater drain; as stormwater percolates through the soil, mulch, compost, and plants pollutants are filtered out, and cleaner stormwater drains to nearby streams. 
