What is 6-PPDq?

All tires have a chemical called 6-PPD that keeps them from cracking and extends the life of tires. Through driving, tiny bits of rubber tire particles containing 6-PPD are shed onto driving surfaces. Roughly 10% of these particles enter waterways via stormwater runoff (rain, wind), where 6-PPD reacts with water to form 6-PPD quinone (6PPD-q). 

This could be a ubiquitous microplastic entering surface water systems in developed areas, making 6-PPDq an emerging contaminant of concern.

6-PPDq is acutely toxic to coho salmon and linked to die off events in the Pacific Northwest. It is also sub-lethally toxic to other salmonid species, including rainbow, brown and brook trout, all species found in the Delaware River Basin.

DRBC Study

In 2023, the DRBC received grant funding from the National Fish & Wildlife Foundation to perform a first of its kind study in the Delaware River Basin to determine the presence of this contaminant in Basin waters.

The study, which began in April 2024, is collecting samples to develop baseline concentrations of 6-PPDq in trout streams. Sampling will continue quarterly for one year with up to 3 additional sample collections after rain events to look at how heavy rainfall affects concentrations.

Initial monitoring sites were selected based on their proximity to paved surfaces and reputation as high quality trout streams.

Sampling Locations

• Upper Basin: East Branch Delaware River, West Branch Delaware River, Sherman Creek, Faulkner Brook, Shehawken Creek, Delaware River at Hancock, Delaware River at Lordville and Equinunk Creek.
• Middle Basin: Dunnfield Creek
• Lower Basin: Bushkill Creek
• Lehigh Basin: Little Lehigh Creek
• Schuylkill Basin: Valley Creek, unnamed tributary to Sixpenny Creek

The DRBC's study was featured in a February 2024 Delaware Currents article authored by Lauren Yates: "DRBC to study chemical from rubber tire particles as source of water contamination".

Additional Monitoring of the Delaware River Mainstem

• From May 2024 through August 2024, 6-PPDq monitoring is added to the Delaware Estuary Water Quality Monitoirng Program at 8 sites from Eddystone up to Biles Channel.

This work will contribute to the development of comprehensive strategies that identify, characterize and evaluate 6-PPDq in DRB waters.

American Chemical Society

• Substance derived from tire debris is toxic to two trout species, not just coho salmon (March 2022)

Interstate Technology Regulatory Council

• Tire Anti-Degradants (6-PPD)
  
  
• Fact Sheet -What We Know: 6-PPD and 6-PPD quinone (pdf)

Society of Environmental Toxicology and Chemistry

• Acute Toxicity Testing of the Tire Rubber–Derived Chemical 6PPD-quinone on Atlantic Salmon (Salmo salar) and Brown Trout (Salmo trutta) (Anders Foldvik, Fedor Kryuchkov, Roar Sandodden, Silvio Uhlig; September 2022)

U.S. EPA

• 6PPD-quinone

U.S. Geological Society

• 6PPD-Quinone