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

What is 6PPD-Q?

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

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

6PPD-Q 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 if 6PPD-Q is present in Delaware River Basin waters under normal and/or stormwater flows.

The study, which was funded from April 2024 through 2025, involved collecting water samples to develop baseline concentrations of 6PPD-Q in trout streams. Sampling continued quarterly for one year, with up to 3 additional sample collections after rain events to look at how heavy rainfall affects contaminant concentrations. Basic water chemistry (for example, pH, dissolved oxygen) was 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.

 

Map of DRBC Study Smapling Locations.
Map of 6PPD-Q Sampling Locations (view as pdf)


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: Sixpenny Creek, Valley Creek and a tributary to Valley Creek (when conditions allow)

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.



Additional Monitoring of the Delaware River Mainstem


Info on DRBC's Study


Data to Date

  • 6PPD-Q was found at every site sampled. Concentrations varied, but nearly all samples were well below known acute toxicity thresholds.

  • We still have a lot to learn, especially about sub-lethal toxicity thresholds.

  • Highest concentrations of 6PPD-Q are associated with stormwater runoff events, especially in the lower basin and near heavily traveled roadways. 


Looking Ahead

  • This work will contribute to the development of science-based, comprehensive strategies that identify, characterize and evaluate 6PPD-Q in DRB waters.

  • DRBC plans to study additional streams using a USGS tool that scores watersheds based on 6PPD-Q threat.
Additional Resources


American Chemical Society


Interstate Technology Regulatory Council


Society of Environmental Toxicology and Chemistry


U.S. EPA


U.S. Geological Society