Refined Tar-based Sealer Status Update

In November 2005 the Austin, TX, city council passed a ban on using refined tar-based pavement sealers (RTS) that went into effect on January 1, 2006. According to news accounts in the Austin American Statesman, the city council relied on “A study released in June by the city and the U.S. Geological Survey…. [that] said sealants might contribute 90 percent to 95 percent of the PAH pollution in urban watersheds” (10/22/2005) and were led to believe that particles of RTS in stormwater runoff was “…a major source of pollution in Austin waterways, including Barton Springs Pool.” (11/19/2005). From the perspective of the industry and unbiased environmental scientists, the city council’s actions the reported reasons for the city’s actions made little sense, especially in light of ta 2003 finding of the U.S. Public Health Service: “We did not find any information to support contention that swimming every day in Barton Springs would result in adverse health effects. Thus, we have concluded that swimming and playing in Barton Springs Pool poses no apparent public health hazard.”

Shortly after the city council vote, before the ban went into effect, members of the Pavement Coatings Technology Center (PCTC, as it was named at the time) retained an environmental science firm to collect sediment samples from Austin waterways and analyze them for the pollutant in question, known as polycyclic aromatic hydrocarbons (PAHs) – a type of organic chemical that occurs everywhere in the urban environment – in food, in wood smoke, in gasoline exhaust, in used motor oil. More than two years later, the firm collected and analyzed samples from the same locations again and compared the results and published the findings in a scientific journal. They found no change in the amount or sources of PAHs in sediments in Austin waterways. In addition to indicating that the ban had not resulted in changes in PAHs in the waterways, the results were also intriguing because the data hinted that the PAH "fingerprint"of sediments in Austin waterways did not match what was known about the PAH signature of RTS.

Following up on this hint, PCTC retained one of the leading experts in PAH forensics (the science of identifying sources of PAHs) to evaluate the U.S. Geological Survey (USGS) assertion, repeated many times since that first Austin, TX, report, that RTS is a major source of PAH pollution in urban watersheds. Critiques of the USGS assertions and analysis of RTS PAH fingerprint data have been publishedin the scientific literature. Most recently, PAH fingerprint analysis has been applied to PAHs in sediments from Austin and Washington, D.C. The city council of the District of Columbia imitated Austin in banning RTS. Forensic analysis of chemical fingerprints of PAHs in sediments in both Austin and Washington show that RTS cannot be an important source of PAHs in either locality.

RTS bans enacted by Austin, Washington, D.C. or any other locality are unlikely to have any effect on concentrations of PAHs in local waterways, and the bans will fall far short of the “90 percent to 95 percent” reduction that was promised in Austin.

PCTC will host a free webinar with behind-the-scenes details on this topic February 26. See the ad page 40. Register at To contact PCTC email or visit