Roadway Runoff Induced Acute Mortality in Juvenile Coho Salmon During Spring Storm Events

Area of Science:

• Environmental Toxicology
• Aquatic Ecology
• Salmonid Conservation

Background:

• Urban Runoff Mortality Syndrome (URMS) causes adult coho salmon deaths in fall due to roadway runoff.
• The primary toxicant is 6PPD-quinone (6PPDQ), a tire-derived chemical.
• Juvenile coho salmon are sensitive to 6PPDQ and inhabit impacted areas year-round, including spring storm events.

Purpose of the Study:

• To evaluate the risk of URMS in juvenile coho salmon during spring storm events in impacted watersheds.
• To compare water quality and mortality of juvenile coho salmon exposed to creek water versus groundwater during spring storms.

Main Methods:

• A field study was conducted at Miller Creek, WA, exposing juvenile coho salmon to creek water or groundwater during three spring storms.
• Water quality parameters, including 6PPDQ concentrations, were monitored.
• Mortality rates of exposed juvenile coho salmon were recorded over 24-73 hour storm exposure periods.

Main Results:

• Peak 6PPDQ concentrations in creek water (73-110 ng/L) exceeded lethal thresholds for coho salmon.
• Approximately 80% mortality was observed in juvenile coho salmon exposed to Miller Creek water during storm events.
• No mortality occurred in control groups exposed to groundwater.

Conclusions:

• Spring storms pose significant, previously unrecognized mortality risks to juvenile coho salmon due to 6PPDQ in roadway runoff.
• These findings highlight substantial year-round water quality challenges impacting coho salmon health and recovery.
• Roadway runoff poses a pervasive threat to coho salmon across all life stages and habitat types.