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Ecology's current work to address 6PPD is highlighted below. Please contact us anytime with questions at 6PPD@ecy.wa.gov.
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Communications and Outreach
Ecology’s 6PPD Team presented at several public forums in September, including:
Finding a Solution
Ecology is focused on several key areas to reduce the threat of 6PPD-quinone on aquatic life. September 2024 efforts to advance research and activities are highlighted below.
Assessing 6PPD-quinone in waterways: research, method development, monitoring, mapping, and modeling to support mitigation planning.
Ecology is partnering with King County and U.S. Geological Survey to measure and compare 6PPDQ concentrations in 28 urban streams. The group will also evaluate passive sampling technologies for monitoring 6PPDQ in waterways.
Reducing sources of 6PPD: tire research, alternatives assessment, and action plan
Reducing 6PPD-quinone in stormwater: mitigation and best management practices
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Stormwater Strategic Initiative Lead (SIL) Funding Opportunity: The Puget Sound Stormwater SIL will open several Requests for Proposal (RFPs) in late October including an investment priority for Chemical Action Plan implementation with recommendations from the 6PPD Action Plan. Information will be posted on the Stormwater SIL’s funding webpage. An upcoming 30-day notice will include a new, simple “intent to apply” online form. Potential applicants should send the form to the Dustin Bilhimer so we can provide resources in the Puget Sound Local Integration Organization. Eligible applicants include local and state governments, Tribes, non-profit organizations, and academia in the Puget Sound region.
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Industrial Stormwater General Permit (ISGP): The ISGP will be reissued in late November 2024. Ecology staff are responding to public comments. These responses will be released alongside permit reissuance.
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New 6PPD Stormwater Best Management Practices (BMP) Effectiveness Website: Ecology published a new webpage to share publications from our 6PPD stormwater research. This page is updated regularly with published deliverables and newly contracted projects.
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Research and Articles
6PPD and 6PPD-quinone research is underway around the world. Below are abstract excerpts from recently published papers that inform Ecology’s 6PPD work.
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Miao et al.: In this study researchers collected tap water samples from Hangzhou, China, and examined seven homologues of PPDQs in collected samples. All target PPDQs were identified in the collected tap water samples, with distinct detection frequencies (38–89%). PPDQs detected in tap water were dominated by N-(1, 3-dimethylbutyl)-N’-phenyl-p-phenylenediamine (6PPDQ; mean 0.56 ng/L, < LOD–4.0 ng/L). The profiles of PPDQs concentrations in tap water from the four districts of Hangzhou city were slightly different. The daily intake (DI) was found highest for 6PPDQ (mean 14–22 pg/kg bw/day, median 10–15 pg/kg bw/day) through tap water intake. The relatively higher DIs of various PPDQs were displayed for infants (mean 10–22 pg/kg bw/day, median 6.5–15 pg/kg bw/day), relative to the children (8.0–18 pg/kg bw/day, 5.4–12 pg/kg bw/day) and adults (6.7–14 pg/kg bw/day, 4.5–10 pg/kg bw/day). These data are crucial for assessing the overall human exposure to PPDQs. This study first, to our knowledge, reveals the concentrations and profiles of PPDQs in tap water.
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Luan et al.: Through a combination of molecular simulation and experimental methods, this study aims to investigate the protection mechanism and conformational relationship of the natural antioxidant gallic acid (GA) and its ester derivatives within the Natural Rubber (NR) matrix. The ultimate objective is to identify natural antioxidants that possess the capability to effectively substitute 6PPD. Simulation results of the chemical aging factor suggest that the phenolic hydroxyl hydrogen dissociation energy of GA is lower than that of the α-H bond of NR, thereby delaying the aging process. Subsequent DPPH radical scavenging experiments, microstructural characterizations, and macroscopic mechanical property tests have confirmed the optimal antiaging properties of octyl gallate in NR, which these ester derivatives are expected to be a nontoxic, nonhazardous, and safe natural antioxidant alternative to 6PPD.
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Lane et al.: Researchers from USGS conducted a reconnaissance of 6PPD and 6PPD-Q in surface waters across the United States from sites (N = 94) with varying land use (urban, agricultural, and forested) and streamflow to better understand stream exposures. Laboratory holding times, bottle material, headspace, and filter materials were investigated to inform best practices for 6PPD-Q sampling and analysis. Glass bottles with PTFE-lined caps minimized sorption and borosilicate glass fiber filters provided the highest recovery. 6PPD-Q was stable for at least 5 months in pure laboratory solutions and for 75 days at 5 °C with minimal headspace in the investigated surface water and stormwaters. Results also indicated samples can be frozen to extend holding times. 6PPD was not detected in any of the 526 analyzed samples and there were no detections of 6PPD-Q at agricultural or forested sites. 6PPD-Q was frequently detected in stormwater (57%, N = 90) and from urban impacted sites (45%, N = 276) with concentrations ranging from 0.002 to 0.29 μg/L. The highest concentrations, above the lethal level for coho salmon, occurred during stormwater runoff events. This highlights the importance of capturing episodic runoff events in urban areas near ecologically relevant habitat or nursery grounds for sensitive species.
Working Groups
Interstate Technology and Regulatory Council (ITRC) Tire Anti-Degradants (6PPD) Team: The ITRC 6PPD Team’s guidance document was recently published. The document provides baseline knowledge on 6PPD and 6PPD-quinone, with a focus on:
- An introduction to 6PPD and 6PPDQ.
- Current knowledge of effects, toxicity, and physical/chemical properties of 6PPD and 6PPDQ.
- The occurrence, fate, and transport of 6PPD and 6PPDQ in the environment.
- An overview of measuring, mapping, and modeling techniques for these chemicals.
- Discussion of mitigation measures, solutions, policies, regulations, and laws.
- An overview of information gaps and research needs.
Stormwater Work Group (SWG): The SWG met in-person with a hybrid meeting for the first time since since 2020. At this meeting, SWG members heard about the Stormwater Action Monitoring (SAM) nearshore mussel monitoring program, updates from partners, discussed initiating the process for selecting new SAM research studies and updating the SWG charter, and inviting Eastern Washington permittees into the SWG. For more information about this meeting, visit the SWG Webpage.
Upcoming 6PPD Meetings
Additional Resources
Ecology is working to address 6PPD through source reduction, stormwater management, and environmental monitoring. You can sign up to receive future updates and read more about our 6PPD work below.
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