Tracking 6PPD-Quinone Dynamics in a Coho Salmon-Bearing Stream Following Rain Reveals Elevated Concentrations for Multihour Periods During High Flow

Urban runoff mortality
syndrome in coho salmon (Oncorhynchus
kisutch) is attributed primarily to N-(1,3-dimethylbutyl)-N′-phenyl-p-phenylenediamine-quinone
(6PPD-Q), principally from car tires, that is delivered to streams
by surface runoff. However, time-resolved stream 6PPD-Q concentration
data remain scarce. We measured rainfall, discharge, and 6PPD-Q concentrations
in an urban salmon-bearing stream over four rain events to capture
the antecedent dry weather (baseflow) and the increased streamflow
(stormflow). Portable autosamplers proved to be effective for continual
water sampling. The resulting time series revealed 6PPD-Q flushing
during stormflow, likely influenced by surface runoff from roads upstream.
Following the initial rise in stream stage (+5% depth), mean 24 h
time-averaged 6PPD-Q concentration was 45.0 ng/L, 25-fold higher than
baseflow, and the mean 24 h load was 3.73 g, 220-fold higher than
the preceding 24-h period. Measured 6PPD-Q concentrations, which peaked
at 237.0 ng/L, exceeded the LC50 reported for juvenile
coho salmon for periods ranging from 3.5 to 18.7 h during rain events,
but never during the preceding dry period. Accordingly, coho salmon
habitat can be subjected to repeated pulses of 6PPD-Q over the course
of the wet season during elevated streamflow periods, which may expose
spawning adults, juveniles, and hatching fry to toxic concentrations
for considerable periods.