Refined tar-based sealers (RTS) have become one of the most debated topics in the pavement coatings industry. Over the past decade, environmental concerns about polycyclic aromatic hydrocarbons (PAHs) have led to bans on RTS in several jurisdictions, including Washington State and Suffolk County, New York. However, a growing body of scientific research challenges the assumptions underlying these bans. The Pavement Coatings Technology Council (PCTC) has funded peer-reviewed studies that question whether refined tar-based sealers are actually a significant source of PAHs in the environment. Understanding the science behind sealcoating mix designs and their environmental impact is essential for contractors, specifiers, and policymakers alike.
What Are Refined Tar-Based Sealers and Why Are They Used?
Refined tar-based sealers are pavement coatings derived from coal tar, a byproduct of the coking process used in steel manufacturing. Unlike raw coal tar, refined tar-based sealers undergo processing to remove impurities and create a consistent, high-performance product. These sealers have been a staple of pavement maintenance programs for decades, valued for their durability and protective qualities.
Performance Advantages of RTS
The primary reason contractors and property owners choose RTS over alternative products is performance. Refined tar-based sealers offer several measurable advantages:
- Superior resistance to petroleum spills, including gasoline, oil, and hydraulic fluid
- Enhanced UV protection that slows asphalt oxidation and surface degradation
- Stronger adhesion to existing asphalt surfaces, reducing delamination risk
- Longer service life, typically 3 to 5 years compared to 1 to 3 years for asphalt emulsions
- Deeper, more consistent color that provides a uniform appearance across large paved areas
Common Applications for Refined Tar-Based Sealers
RTS is specified most frequently for commercial and industrial applications where the extra durability justifies the higher material cost. Typical projects include:
- Shopping center parking lots with high traffic volumes
- Gas station and convenience store pavement exposed to fuel spills
- Industrial facility drive lanes and loading areas
- Apartment complex parking areas and access roads
- Municipal parking lots and public works yards
For these applications, the high-traffic pavement maintenance strategies employed by contractors often depend on the superior chemical resistance that RTS provides.
The Science of PAHs: Sources, Fingerprints, and Misconceptions
The controversy over RTS centers on polycyclic aromatic hydrocarbons, a class of hundreds of chemically related compounds that occur naturally in fossil fuels and are produced by combustion. The USGS published studies suggesting that RTS was a primary source of PAHs in urban sediments, but subsequent analysis has challenged these conclusions.
What the USGS Studies Actually Found
USGS research examining sediments from lakes and streams near paved surfaces detected PAHs in concentrations that varied widely by location. The agency used a mathematical model to attribute PAH sources, concluding that coal tar-based sealers contributed significantly to PAH levels in certain water bodies. These findings were widely cited by environmental groups and formed the basis for regulatory action in multiple jurisdictions.
However, the USGS methodology relied on an analytical approach that had not been validated for sediment fingerprinting. The model was adapted from air pollution research and applied to environmental sediment samples without the calibration needed for accurate source attribution.
PCTC-Funded Research and Fingerprint Analysis
PCTC commissioned independent research using established forensic fingerprinting techniques to re-examine the USGS data. These studies produced findings that directly contradicted the USGS conclusions:
- A before-and-after study in Austin, Texas, showed that PAH levels in sediments remained unchanged after the 2006 ban on RTS, indicating that other sources were responsible for the PAHs detected.
- Fingerprint analysis of USGS data demonstrated that RTS could not be identified as a predominant, significant, or even identifiable part of the PAH mixture in sediment samples.
- Critical evaluation of the USGS mathematical model showed that it lacked the specificity needed for accurate source identification and would produce false attributions under real-world conditions.
Key Differences Between Analytical Approaches
| Factor | USGS Model Approach | Forensic Fingerprinting |
|---|---|---|
| Method origin | Adapted from air pollution modeling | Developed for sediment source attribution |
| Validation | Not validated for sediment analysis | Extensively validated in peer-reviewed studies |
| Specificity | Low; produces false positives for RTS | High; distinguishes between multiple PAH sources |
| Data requirements | Limited; uses ratio-based comparisons | Comprehensive; uses full PAH profile analysis |
| Peer review status | Methodology questioned in subsequent studies | Accepted in multiple scientific journals |
Regulatory Actions and Their Real-World Impact
Despite the scientific uncertainty, several jurisdictions moved forward with bans on refined tar-based sealers. The consequences of these decisions provide important lessons for the industry.
Washington State: A Statewide Ban Without Scientific Support
In 2011, the Washington State legislature passed and the governor signed a bill banning refined tar-based sealers statewide. This action was taken despite a study from the state’s own Department of Ecology showing that RTS was, at most, a vanishingly small contributor to PAH levels in Washington sediments. The USGS model had attributed more than half of all PAHs in Seattle’s Lake Ballinger to RTS, but fingerprint analysis showed the actual contribution was close to zero percent.
During legislative hearings, PCTC representatives observed considerable animus toward any material associated with coal, regardless of the scientific evidence. Several legislators publicly celebrated the closure of Washington’s last working coal mine and discussed efforts to ban coal exports from the Port of Seattle. This political context may have influenced the outcome more than the scientific data.
Suffolk County, New York: Clean Water Act Data Ignored
A similar pattern emerged in Suffolk County, New York, where legislators passed a ban despite comprehensive data collected as part of Clean Water Act compliance showing that no sediments or water bodies in the county contained excess PAH levels. The USGS model attributed more than half of PAHs in Newbridge Pond to RTS, but fingerprint analysis indicated that RTS could have contributed only a small percentage, if any.
The ban passed despite testimony from a PCTC member who had been a responsible manufacturer in Suffolk County for many years, and despite eloquent opposition from local contractors who understood the practical implications.
Economic Consequences for Contractors and Property Owners
The bans have had measurable economic impacts on the pavement maintenance industry:
- Alternative sealers cost 20 to 40 percent more per gallon than RTS
- Shorter service life means more frequent reapplication, increasing long-term maintenance costs
- Contractors lost access to a product they had used successfully for decades
- Reduced competition in the sealer market led to higher prices for all products
- Property owners faced unexpected increases in pavement maintenance budgets
Understanding how asphalt cracks and potholes form in different climates helps explain why the protective qualities of RTS are particularly valuable in regions with freeze-thaw cycles and heavy deicing chemical use.
Navigating the Future of Pavement Sealers
The refined tar-based sealer debate is ongoing, with new scientific findings continuing to emerge. Regardless of the regulatory outcome in individual jurisdictions, the pavement maintenance industry must adapt to changing conditions while maintaining service quality.
Alternatives to Refined Tar-Based Sealers
For contractors operating in jurisdictions with RTS bans, several alternative products are available:
- High-performance asphalt emulsions with polymer modifiers that improve durability and chemical resistance. These products have improved significantly in recent years and can approach RTS performance in some applications.
- Acrylic-based sealers that provide excellent UV resistance and color retention, though at a higher cost per square foot. These are often specified for decorative or high-visibility projects.
- Coal tar and asphalt hybrid formulations that blend the durability of coal tar with the lower PAH content of asphalt emulsions. These products are available in some markets and offer a compromise between performance and environmental profile.
Industry Advocacy and Science-Based Regulation
PCTC and other industry organizations continue to advocate for regulation based on sound science rather than political pressure. The organization has committed to:
- Funding additional peer-reviewed research on PAH fingerprinting and environmental fate
- Engaging with regulators at the local, state, and federal levels to present scientific findings
- Educating contractors and property owners about the performance benefits of RTS
- Supporting the development of improved products that address environmental concerns while maintaining performance
Looking Ahead: Sustainable Pavement Preservation
The pavement coatings industry is also exploring broader innovations in sustainable materials and practices. Concepts like net-zero asphalt pavements through industry partnerships represent the kind of forward-looking thinking that can address environmental concerns without sacrificing the performance that property owners and contractors depend on.
The debate over refined tar-based sealers highlights the importance of rigorous science in environmental regulation. When political considerations override scientific evidence, the result can be regulations that harm small businesses and increase costs for property owners without delivering measurable environmental benefits. For the pavement maintenance industry, staying informed and engaged in the regulatory process is essential for protecting both business interests and the quality of pavement preservation services.