6PPD-quinone biomonitoring of salmon and mussels in Puget Sound, WA, USA

6PPD-quinone (6PPD-Q) is a transformation product of tire rubber anti-oxidant 6PPD and is the causal toxicant for the urban runoff mortality syndrome (URMS) observed in coho salmon (Oncorhynchus kisutch) and other salmonid species. While 6PPD-Q has been measured in air, water, and sediments, data on 6PPD-Q body burdens in aquatic biota is limited. Here we conducted biomonitoring of 6PPD-Q in caged bay mussels (Mytilus trossulus) and juvenile Chinook salmon (O. tshawytscha) from nearshore sites and river estuaries across Puget Sound, WA, as well as a year-long water monitoring from three urban streams in the Seattle area with well-documented URMS history. Low 6PPD-Q concentrations <1 ng/g (ww) were found in both mussels and Chinook salmon, with overall detection frequency of 49% and 30%, respectively. 6PPD-Q was detected primarily in mussels located adjacent to metropolitan areas, while the majority of Chinook salmon with detectable 6PPD-Q were collected from the highly urbanized Green/Duwamish River estuary. Seasonal and highly dynamic 6PPD-Q levels were observed in the water of urban streams, with correlations between 6PPD-Q levels and hydrological parameters (precipitation, stream discharge). Urbanized areas exhibit more frequent 6PPD-Q detections, which correlates with higher road density and increased percentages of impervious surfaces. While the detection of 6PPD-Q in aquatic organisms is likely influenced by specific locations (hot spots) and high rainfall events (hot moments), monitoring its presence in fish and shellfish tissues offers limited utility for exposure assessments. This is primarily due to the infrequent detection and low concentrations of the compound in these tissues.