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Contaminants of Emerging Concern: 6-PPDq
DRBC staff collects a water sample from Valley Creek to monitor for 6-PPDq. Photo by the DRBC.
DRBC staff collects a water sample from Valley Creek
to monitor for 6-PPDq. Photo by the DRBC.

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 and is funded through 2025, involves collecting water 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. Basic water chemistry (for example, pH, dissolved oxygen) will be assessed as part of each sampling event.

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

DRBC staff collects a water sample from Pennsylvania's Little Lehigh Creek. Photo by the DRBC. Water sample bottles and a clipboard at Sherman Creek, one of the sampling locations. Photo by the DRBC. DRBC staff stands by the Delaware River at Lordville holding line for the water quality meter. Photo by the DRBC.
DRBC staff collects a water sample
from the Little Lehigh Creek. Photo
by the DRBC.		 Water sample bottles and a clipboard
at Sherman Creek, one of the sampling
locations. Photo by the DRBC.		 DRBC staff stands by the Delaware
River at Lordville holding line for the
water quality meter. Photo by the DRBC.

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

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

American Chemical Society

Interstate Technology Regulatory Council

Society of Environmental Toxicology and Chemistry

U.S. EPA

U.S. Geological Society