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Field and lab tests show high‑performance bioretention media can reduce 6PPD quinone below Washington criteria

6PPD State of the Science Forum (Day 2) · December 10, 2025
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Summary

Multiple laboratory and field studies presented at the forum show high‑performance bioretention media and some floating treatment wetland designs reduce 6PPD quinone concentrations substantially; treated effluents often fell below Washingtons acute aquatic life criterion (12 ng/L) and did not cause acute coho mortality in lab exposures.

Researchers and practitioners reported consistent lab and field evidence that high‑performance bioretention media can reduce 6PPD quinone concentrations in stormwater to levels below Washington States acute aquatic life criterion and substantially reduce acute mortality risk to coho salmon.

In laboratory column tests led by King County and Washington State University partners, influent concentrations from heavily contaminated I‑5 Ship Canal stormwater (about 200to800 ng/L) were treated through three different high‑performance soil media blends. Chelsea Mitchell of King County said effluent concentrations from the high‑performance media ranged from below detection to about 5 ng/L and "always met" Washington's 12 ng/L acute criterion; conventional 60/40 (sand/compost) media produced more variable…

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