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The Facts about Refined Tar Sealers (RTS) & PAHs

The Facts about Refined Tar Sealers (RTS) & PAHs

by Girish Dubey, Star Seal, Inc.


Over the last few years, more precisely since the ban on the use of RTS in Austin, TX, in January 2006 there has  been a great deal of enthusiasm amongst counties, municipalities, cities and states in various parts of the U.S.  to jump on the band wagon and challenge the safety of RTS. As a result, RTS has been banned in some cities and most recently by the state of Washington where no RTS is used anyway.  The news stories that have appeared in the past have taken off on the RTS ban stories creating concern with the public-at-large. They apparently have not taken time to find the facts and have jumped the gun to sell their stories for the sake of  sensationalism. 

How did this whole issue originate? Back in 2004-05, the City of Austin water quality management department collaborated with a couple of researchers at the United States Geological Survey (USGS), to investigate contributors to the PAHs level in the water sediments of the Barton Springs.   The USGS researchers did an excellent job in “connecting the dots” and declared that the majority of the PAHs in Barton Springs water sediments was caused by the RTS applied on the parking lot of an apartment complex uphill from the Barton Springs pool. This is a classic example of fabricating evidence to suit the goals. The same researchers, in their previous publications had concluded that the increasing levels of PAHs in urban waters were caused by the increased urbanization, without any mention of RTS. Over the years, Pavement Coatings Technology Council (PCTC), the seal coating industry’s technical organization has done an extensive research in collaboration with the world class research organizations and have established that the;

A. Refined tar sealers are not the main contributors to PAHs accumulations in water sediments,  concluded from fingerprinting (of myriad of sources) studies of water sediments. 

B. PAHs levels in Barton Springs and other locations in Austin have not changed in the last 2.5 yrs. since the ban in Jan. 2006.

C. USGS studies are grossly flawed and have been overly extrapolated to find a scapegoat (RTS).

Armed with its own independent studies, PCTC is responding head-on the challenges at various legislative and regulatory levels that is facing not only the RTS but asphalt based sealers as well, since asphalt also contain PAHs.  Now let’s review some basics.

What are the PAHs?

Polycyclic Aromatic Hydrocarbons (PAHs) are a class of natural organic chemical compounds consisting of carbon and hydrogen atoms combined in thousands of different ways.  A few hundred of the more common combinations have been named, and are sometimes considered separate chemicals.  They are ubiquitous in nature and the environment surrounding us. 

PAHs occur as complex mixtures and not as single compounds.  PAHs are primarily introduced into the environment as by-products of incomplete combustion.  These combustion sources are numerous, including natural sources such as volcanic eruptions, forest fires as well as industrial processes, transportation, energy production and use, food preparation, smoking tobacco, and disposal activities such as open trash burning, auto exhaust, etc.  Such sources are called Pyrogenic since they generate PAHs through burning /combustion activities.  Another major classification for PAHs source is called Petrogenic, PAHs (literally, PAHs from rocks), meaning they are a part of the composition of some materials, e.g. coal, coal tar, crude petroleum, asphalt. They get in the environment through motor oil dripping, tire abrasion, asphalt road paving etc. A few PAHs are used in medicines and to make dyes, plastics, and pesticides. They are found throughout the environment in the air, water, and soil. 

 The movement of PAHs in the environment depends on properties such as how easily they dissolve in water, and how easily they evaporate into the air. PAHs in general do not easily dissolve in water. They are present in air as vapors or stuck to the surfaces of small solid particles. They can travel long distances before they return to earth in rainfall or particle settling. Some PAHs evaporate into the atmosphere from surface waters, but most stick to solid particles and settle to the bottoms of rivers or lakes. In soils, PAHs are most likely to stick tightly to particles. Based on these facts, it is logical to expect that the PAH concentrations would increase (an established fact) with population and urbanization growth. 

Unlike metals, PAHs are organic compounds (contain carbon) and therefore can degrade in the environment.  In aquatic environments, PAHs biodegrade (that is, are broken down by micro-organisms) to a greater or lesser degree depending on a wide variety of factors.  PAHs can also be degraded by sunlight and atmospheric oxidation.  Degradation is more rapid for some PAHs than for others so that, in the context of a human life time, some PAHs have been described as persistent. PAHs can enter the environment from “point sources,” such as municipal or industrial outfalls, or “non-point sources,” such as rainfall, runoff, or atmospheric deposition. 

What’s the problem with PAHs?

• The U.S. Environmental Protection Agency (EPA) lists 16 PAHs as Priority Pollutants.  

• Seven of the 16 are listed in the U.S. Report on Carcinogens (  

• one is classified as a known human carcinogen,  

• Seven are classified as likely to be human carcinogens, which generally means that tumors have been found in experimental animals exposed to high concentrations of the substance. 

• Nine of the 16 are not classified as carcinogens.  The U.S. Report on Carcinogens list is consistent with the list developed by the World Health Organization’s International Agency for Research on Cancer (IARC). 

Because PAHs are practically insoluble in water, they tend to be concentrated in soils and sediment.  In aquatic environments, bottom-living and bottom-feeding organisms can come in contact with PAH-contaminated sediment.  Impacts of PAHs on the health of aquatic organisms are widely studied and many books and scholarly papers are available on the topic.  In general, PAHs with lower molecular weights can be acutely toxic when present at elevated concentrations but are generally non-carcinogenic to aquatic organisms.   PAHs with higher molecular weights are generally not acutely toxic to aquatic organisms, but a number of them are classified as possible carcinogens. 

Interactions between aquatic organisms and PAHs in sediments are exceedingly complex.  Scientists who have worked extensively on the problem agree that the occurrence of adverse biological effects is difficult to predict using only concentration data.  The likelihood of adverse biological effects at any particular location depends on a host of factors, including the sensitivity of species present and the bioavailability of the PAHs at the location.  Bio-availability in turn depends on factors such as physicochemical properties, geochemical and biological factors, and even the source of the PAHs.  For example, there is some evidence that PAHs from coal-related sources are less bio-available than petroleum-related sources, which are thought to be more readily desorbed from sediment particles.


Considering the numerous sources of PAHs, it is illogical to blame RTS as the major source of PAHs; the forensic studies have established that RTS are not a significant source. The noteworthy points are;

• In so far as threat to human health is concerned, there has not been even one known case of cancer, over the 60 years of the use of RTS. 

• There are no published studies linking the use of RTS (during and after application) to harmful effects in humans or animals.  The emissions have been found to be well below the permissible air quality limits both during the application and manufacturing of the RTS. 

• The International Agency for Research on Cancer (IARC) has not classified RTS or the RT (Refined Tar) used to manufacture coal tar sealer as a human carcinogen. 

• No epidemiology studies have been conducted which show a cancer link to Refined Tar-based sealers. 

• The references made by the published news stories to the incidence of scrotal cancer in chimney sweeps during the 1770s have been attributed to poor personal hygiene and involved chimney soot which is not analogous to refined coal tar. 

• Similarly, references to the carcinogenicity of RTS on MSNBC Internet Article on Refined Tar‐Based Sealers and creosote are completely false. Creosote is NOT classified by IARC as a human carcinogen. This fact is supported by a 2005 epidemiology study completed by Wong and Harris (Wong and Harris, Journal of Occupational and Environmental Medicine, Vol. 47, pages 683-697, July 2005) who found no increase in mortality for creosote wood treating workers from any causes including cancer. 

• Additionally, the US Food and Drug Administration (FDA) has authorized use of coal tar soaps, ointments and shampoos for treatment of seborrheic dermatitis, psoriasis and atopy (eczema) based on epidemiological data submitted to FDA by Neutrogena Corporation. 

Independent Studies have proven that USGS Austin/Barton Springs studies were flawed.  Research, including a scientific review of the Austin study, commissioned by the PCTC shows that crankcase oil and vehicle emissions, not runoff from pavement sealed with refined tar sealer, is consistently identified as the primary source of PAHs found in the urban environment. In a scientific review of the Austin studies, conducted by Dr. Robert DeMott and ENVIRON International, the PAH samples in soil and roadway runoff materials in Austin were found to be consistent with typical urban background levels of PAHs. Dr. DeMott found no cause for concern for elevated exposure from PAHs in the water or soil. Because so many other “activities of urbanization'' are proven sources of PAHs, including vehicle exhaust, motor oil, rubber tires particles and debris from asphalt roads. As mentioned in the introductory paragraphs, a follow-up study conducted by ENVIRON International sampled sediments in Austin before and approximately 2.5 years after the city banned the use of RTS showed no discernable difference in either the amount or types of PAHs were found in the before and after samples.

US Agency for Toxic Substances and Disease Registry (ATSDR) – The City of Austin decided to institute a ban on refined tar-based sealant even though a health consultation conducted by the ASTDR concluded: “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”. This is an important study and significant findings which were completely ignored by news stories. 

House Dust Study -- Chemicals found in house dust samples and that comprise polycyclic aromatic hydrocarbons (PAHs) are ubiquitous in the environment and come from many sources.  Individual components of PAH mixtures have widely differing health effects. The reported finding of the presence of the PAH substance benzo(a)pyrene in driveway dust "thousands of times the level that would trigger a cleanup at a toxic-waste site" is irresponsibly alarmist and lacks evidence as to its origin or its purported relationship to sealant. The study's evaluation of other sources of PAHs in house dust is incomplete and inadequate to draw the conclusions cited. 

Best Management Practices (BMP) for Sealcoatings.

What are options for reducing or preventing impacts from PAHs in paving materials? While there is no evidence that RTS are a significant important sources of PAHs in sediments, and reduction in use of refined coal tar-based sealants is unlikely to result in any noticeable decrease in PAHs either already in sediments or that is deposited in sediments in the future, PCTC members recommend that manufacturer’s specifications be followed to limit the possibility of environmental releases.  Specific recommendations include: 

A. Make sure no significant rainfall is forecast for at least 48 hours after application of the sealcoat; 

B. Only apply sealcoat when temperatures are above 60° Fahrenheit and rising throughout the application period; 

C. Take appropriate measures to ensure that newly applied sealcoat does not  impinge on adjacent surfaces or enter storm or sewer drains; and 

D. Make sure that no traffic can access the newly sealcoated surface for at least 12 hours.   

E. Asphalt-based sealants also contain PAHs. Manufacturer’s specifications must also be followed during application of asphalt-based sealcoat. Asphalt on high speed roadways, on roofs and other surfaces are sources of PAHs, as are gasoline spills, oil and lubricant leaks and materials abraded from tires.  To minimize PAHs in the environment, avoid spills and leaks and make sure equipment is in optimal working order. 

F. Concrete parking lots do not require sealants, but do collect PAHs from spills, leaks, abrasion and atmospheric deposition which may be washed into streams during rain events.  To minimize PAHs in the environment, avoid spills and leaks and make sure equipment is in optimal working order. 

G. A North Carolina State University study found a reduction in the concentration of PAHs from parking lot runoff after treatment by a vegetated bio-retention cell.  Installing bio-retention cells (also called rain gardens, or plant beds) to treat parking lot runoff may reduce PAHs, as well as other pollutants, in storm water runoff. 

H. Some proprietary storm water management devices are marketed to reduce organic matter such as PAHs in runoff. 

It is noteworthy that both Texas Commission on Environmental Quality (TCEQ) & U.S. E.P.A. Concluded that Barton Springs were safe for swimming, contrary to City Of Austin & U.S.G.S. & it’s “Findings”. 

Other than Austin RTS is not banned in any part of TX. None of the cities which either banned RTS (Madison, WI and Washington, DC, some small cities in MN and now Washington State)or are considering to ban has done their own studies. They are depending upon the erroneous data propagated by the USGS researchers. 

Refined Tar Sealers use a purified grade of coal tar, RT-12  The opponents often confuse or deliberately ignore the fact that RT-12 has much smaller percentage of PAHs compared to crude coal tar. 

Refined Tar Sealers in both wet and dry form are not considered hazardous. Also there are no “Hazard” shipping and placarding requirements for transporting RTS.


The fact that USGS studies which have become the “Ground Zero” studies for most cities or states ,which are considering to ban RTS, are  grossly flawed. RTS though a source is an insignificant source of PAHS, not the major source. There has been no evidence that RTS harm the humans, animals or the environment.  Both refined tar based and asphalt based sealcoatings, are engineered industrial coatings that shall be handled, stored and applied per manufacturer’s instructions while observing all precautions and care as not to let them contaminate the bodies of water and soil.  For additional reading , please visit the following websites;

Girish Dubey is the President of Star Seal Inc., 1150 Milepost Road, Columbus, OH 43228, 1.800.759.1912, Tel.  614.870.0744, Fax. 614.870.0598,