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City seeks Ecology funding to monitor 6PPDQ in stormwater after research links tire chemical to fish kills
Summary
City staff requested consent for about $88,000 in Ecology-funded monitoring of 6PPDQ, a transformation product of a tire antidegradant linked to coho salmon mortality. The proposed work would sample paired catch basins to measure how much 6PPDQ is captured by gray stormwater infrastructure.
The city submitted a proposal to the Washington State Department of Ecology to monitor 6PPDQ in urban stormwater and asked the PIES Committee for consent for about $88,000 in Ecology-funded work, presenter Trey said.
Trey described 6PPD as a tire additive that reacts with ozone to form 6PPDQ, the compound researchers identified as lethal to coho salmon and toxic to rainbow trout. "6PPDQ is what we're actually gonna focus on... 6PPDQ is lethal to coho salmon and toxic to rainbow," Trey said, adding that early discoveries were made around 2020 by researchers at the Washington Stormwater Center and that the issue has driven statewide and national research and policy attention.
Trey said the city's proposed monitoring would install a catch-basin insert on an upstream basin and place a monitor on a downstream basin to compare influent and effluent concentrations and estimate how much 6PPDQ is removed by typical gray-infrastructure catch basins. He noted limited information exists about how much 6PPDQ binds to sediment in catch basins and how much might pass through the system to receiving waters such as the Spokane River.
Toxicology figures cited in the presentation show coho mortality at very low concentrations (0.08 micrograms per liter for coho salmon), with higher thresholds for trout species; Trey said the highest concentration reported in the literature to date was about 2.8 micrograms per liter in urban stormwater samples. He said Ecology is funding municipalities and universities across the state to broaden monitoring and that the city's proposed work would leverage existing monitors when possible.
Questions from committee members focused on next steps if concerning concentrations are found and whether existing infrastructure such as combined-sewer-overflow (CSO) tanks would sequester 6PPDQ. Trey said Ecology-funded studies statewide are intended to answer those questions; early work shows green stormwater infrastructure like swales can sequester 6PPDQ but many pipes still discharge untreated stormwater to receiving waters. He said it is not yet known to what degree CSO tanks would remove the compound.
Discussion versus decision: staff requested consent for a monitoring proposal and explained technical background; committee members asked follow-up questions. The Ecology grant and study design aim to inform potential mitigation actions, but no mitigation decision was made at the meeting.
Next steps: staff will proceed with the Ecology proposal process and return results to the committee after monitors are installed and samples analyzed.
