Stormwater Management to Address Highway Runoff Toxicity Associated with Tire Wear
Research Idea Scope
Recent research findings identified 6PPD-quinone as the major agent responsible for exceptionally high levels of rapid mortality of adult Coho salmon in some urban streams. Lethal effects occurred in Coho at very low concentrations of 6PPD-quinone. Related studies have found the chemical is also toxic to rainbow trout, and King Salmon, and other aquatic species may be at risk as well. So far, the lethal impact, presumably from 6PPD-quinone, has only been documented in urban streams that receive runoff from high average daily traffic (ADT) highways.
6PPD is a chemical added to tires to increase their life by reducing tire oxidation. It has been used for over 40 years in almost all tires and is assumed to be ubiquitous in roadway runoff, as are tire particulates that have been detected in fish across the country. Potential sources of 6PPD-quinone in stormwater include tire wear particulates, abrasion of pavement that contains tire derived aggregate (TDA), and potentially leachate from fill incorporating ground tires. Although standard analytical test methods are not yet available, researchers have detected 6PPD and linked it to toxicity in runoff; standard methods are currently under development by the WA Department of Ecology.
Questions of importance for DOTs are: 1) Under what conditions and where is 6PPD-quinone related toxicity an issue, 2) what highway related and receiving water factors are implicated, and 3) what drainage characteristics and stormwater management techniques are capable of reducing or eliminating the toxicity of highway runoff due to 6PPD-quinone and other pollutants (zinc, copper, PAHs, etc.).
There are also concerns about use of TDAs in the roadway environment. DOTs and other transportation agencies will be a primary target of regulatory efforts to address 6PPD-quinone toxicity. Projects have already been delayed due to uncertainty as to where, what type, and how much treatment of roadway runoff is necessary.
The research, identified as a priority for a Research Needs Statement by the TRB AKD50 Stormwater Subcommittee, will 1) identify where and what features within the highway environment contribute acutely toxic runoff associated with 6PPD-quonine and 2) identify and develop practical treatment facilities and stormwater management approaches that can be used in urban and rural areas.
The objective of this research is to identify under what conditions runoff intervention is needed and develop and provide design guidance for stormwater treatment and management techniques that substantially reduce or eliminate highway runoff toxicity, as well as 6PPD-quinone specifically. Toxicity testing is vital because there is no formal toxicity criteria for 6PPD-quonine, and other components of highway runoff likely affect toxicity as well.
Major tasks or activities:
• Literature review on 1) highway runoff toxicity, with an emphasis on 6PPD-quinone toxicity and 2) effectiveness of treatment and stormwater management, including the effect of vegetated drainage system types on toxicity reduction.
• Field collection of highway runoff and laboratory analyses to:
i. Assess toxicity reduction of high traffic highway runoff routed through bare soil, compost amended soil and vegetated conveyances
ii. Design and conduct a laboratory study to determine filtration material characteristics and mechanisms (such as layer thickness, infiltration rate, contact times, etc.) necessary for effective toxicity and/or 6PPD-quinone concentration reduction by BMPs
iii. Conduct selected 6PPD-quinone leachability tests for tire derived aggregate/crumb rubber containing pavement materials
• Identify the components and features of the highway system and receiving waters that affect 6PPD-quinone toxicity and its impacts.
• A report that provides 1) guidance on identifying situations where 6PPD-quinone targeted BMPs are appropriate to avoid toxic impacts, 2) an initial assessment of the potential for TDAs to contribute to toxicity, and 3) design criteria for 6PPD-quinone targeting BMPs. Research documenting toxicity reductions by drainage systems and BMPs etc. should be prepared for peer reviewed publication.
Urgency and Payoff
The demonstrated toxicity of 6PPD-quinone for at least one listed Threatened and Endangered species and the potential for toxic impacts to other aquatic species means that regulatory agencies will likely impose treatment requirements on highway projects. It may also limit the ability to use recycled tire paving products that meet other agency environmental goals. Permit conditions could include requirements for retrofits as well as new/re-development projects. This research will help inform cost-effective solutions for DOTs to implement as well as appropriate regulatory requirements.
Without this research, regulatory requirements may be based on insufficient information, resulting in overly broad requirements, misapplied and misdirected resources, and implementation of BMPs where they are not necessary and so provide no appreciable benefit, or conversely do not provide sufficient treatment. Also, regulatory requirements may be ad hoc, providing no consistency and creating confusion, inefficiencies and delays.
As a result of this research, DOTs will have the information necessary to better understand where to focus more specific treatment efforts to effectively manage highway runoff for 6PPD-quinone toxicity. Regulatory agencies will have a better understanding of stormwater management options and treatment methods that reduce and/or remove toxicity. Sensitive aquatic species will benefit from reduced toxicity in their environment. Lastly, knowledge regarding the potential release of 6PPD-quinone and its toxicity will help DOTs in selection and placement of paving materials that are composed in part of TDA.