King County scientists have developed a soil mix to address the environmental issue caused by 6PPDQ, a harmful chemical found in tire dust. The chemical has been negatively affecting coho salmon, an important species in the Pacific Northwest. The new soil mix aims to stop the chemical from impacting the salmon population, according to the King County.

King County has developed a bioretention soil made of sand, coconut fiber, and biochar to filter out 6PPDQ, a harmful pollutant. Laboratory tests showed that nearly all coho salmon in untreated stormwater died, while those in water filtered by the soil survived and thrived. Josh Latterell from the King County Water and Land Resources Division said, "It's not every day that we get to say with certainty that we can solve such a complicated problem, but I feel hopeful about this one." A full-scale pilot of the soil will be conducted in Whatcom County by the end of the year to test its effectiveness in real-world conditions.

King County is working to address 6PPDQ contamination by targeting tire chemical hotspots and collaborating with partners like the Washington State Department of Transportation to prioritize intervention sites. A new soil mix, included in updated stormwater management guidelines, will be tested in unincorporated areas. Chelsea Mitchell, a Senior Ecotoxicologist at King County's Water and Land Resources Division, stated, "The urgency of the 6PPDQ problem is leading to a lot of research, coordination, resources, and general societal investment." The effort aims to improve water quality and help restore coho salmon populations.