Science & Health

PCTC’s Statement on Maine Legislation

PCTC believes that the Maine legislation was based on US Geological Survey (USGS) research that claims that refined tar sealers (RTS) are the main source of polycyclic aromatic hydrocarbons (PAHs) in the environment, when in fact the contribution attributable to sealers has been shown by other research to be minimal. The USGS study has proven not to be trustworthy, accurate or reproducible. Independent studies indicate that RTS poses little to no risk to health or the environment.

Coal tar is classified as “generally regarded as safe and effective” by the Food & Drug Administration. RTS has a long history of safe use in the pavement maintenance industry, and PCTC maintains that sealing asphalt surfaces will extend their useful lives many times over, saving natural resources and increasing long-term sustainability.

PCTC White Papers


Health Effects of Human Exposure to Products Derived from Coal Tar or Containing Coal Tar asked Dr. Brian Magee, a toxicologist with expertise in PAHs and in risk assessment, to review a paper claiming to show that people living near paved surfaces sealed with RTS have an elevated risk of cancer. The conclusions of Dr. Magee’s peer review report include the following statement. The long history of use of coal tar as a therapeutic agent demonstrates that coal tar exposures do not increase people’s risks of cancer. There is no evidence that low level or intermittent exposure to coal tar or coal tar pitch has caused cancer in humans. There is little evidence that high level repeated exposures have caused cancer in humans. There are some studies about high temperature industrial processes such as aluminum smelting or coke oven gases that show some adverse effects but these studies have no relevance to coal tar sealants. Read the entire report here.

Refined Tar-Based Sealers

The peer review report mentioned above also concluded that: “Although PAHs are present in coal-tar-based sealants, there is no evidence that coal-tar-based sealants affect people‟s health. Furthermore, there is no evidence that people who intentionally put pure coal tar on their skin cause health risks. In fact, there is good evidence that it does not.” Read the whole peer review report here.

Ready-to-use pavement sealers (both refined coal tar and asphalt based) have never been cited for a claim of bad health due to the use of it’s sealers. Sealers are manufactured with high quality ingredients in strict accordance with all federal, state and local requirements.

Air sampling studies showed refined coal tar based sealers pose no inhalation risk to applicators, manufacturers or the general public.

The USGS team that, based on flawed “science” has been conducting a taxpayer-funded advocacy campaign targeting RTS published a “risk assessment” in 2013 purporting that people who live near pavements sealed with refined tar have elevated cancer risks. To reach that conclusion, the “risk assessors” exaggerated exposures, used soil samples collected immediately next to paved surfaces that contained materials not associated with RTS and, in short, violated as many of the “rules” of risk assessment as they needed to achieve a calculated risk above levels of concern. You can read the details here.

Coal Tar Pharmaceuticals

Coal tar has been used to treat people with skin conditions such as dandruff, sebborrheic dermatitis and psoriasis for over 150 years, and today is recognized by the US Food & Drug Administration (FDA)as “generally recognized as safe and effective” (GRASE). The Code of Federal Regulations entry for medicinal coal tar is 21CFR358.

In response to a petition from a private citizen, FDA reviewed the use of coal tar-containing creams, lotions and shampoos to determine whether those products should continue to be available as Over-the-Counter (OTC; which means available without a prescription) medicines. The conclusion reached in FDA’s formal review, completed in 2001 and posted here, was as follows “Our review of information in your petition, comments submitted to the docket, and reports in FDA’s Adverse Events Reporting System did not disclose new evidence that the risk of cancer is greater in consumers who regularly use OTC drug products containing coal tar than in consumers who do not.“.

There are many online sources of information about medicinal uses of coal tar-containing products, for example the Mayo Clinic or WebMD.

What about Exposure to PAHs in Lake Sediment?

First thing to know is that PAHs are virtually insoluble in water. That’s why the focus is on whether PAHs in sediment can be a health hazard to people – and PAHs are rarely found to be a cause of concern even in highly urbanized areas. For example, the City of Austin, Texas was worried about whether PAHs in sediments in Barton Springs Pool – a beautiful recreational area in downtown Austin with a spring-fed swimming pool – might pose a health risk to people swimming in the pool. So they requested the US Public Health Service, in conjunction with the Texas Department of Health, conduct a “health consultation” to evaluate whether the City should be concerned about the health of citizens swimming in Barton Springs Pool. The health consultation report, posted here, contains the following conclusions: “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.” The City asked the Texas Commission on Environmental Quality and the US Environmental Protection Agency to review the Health Consultation. Assured by the findings of the Health Consultation, the City re-opened Barton Springs Pool.

Another thing to know is that has taken a hard look at whether sealers applied to paved surfaces are contributing in any significant way to PAHs in sediments. We’ve funded scientists to look at the data the USGS uses to claim sealers are a problem and to look at other data (there’s a LOT of data available for PAHs in sediments!). We’ve funded scientists to collect new data to help answer questions. With a very few exceptions (mostly, samples collected right next to sealed lots) the PAH signature of RTS is not identifiable in sediments. Take a look at the Research page on this web site – there are many links to papers and presentations documenting efforts to identify whether RTS is an important source of PAHs in sediments. has filed a Data Quality Act Petition asking the USGS to cease disseminating their flawed interpretations of the data. The flaws in USGS interpretations of sediment PAH data are further documented in PCTC White Paper 1301.

To try to minimize any possible release of RTS to sediments, recommends that sealer applicators follow our Best Management Practices.

What about Exposure to PAHs in House Dust?

PAHs are everywhere. They occur naturally in organic materials, and are made whenever organic substances are heated. The peer review report of the USGS research team so-called “risk assessment” contains a summary of typical sources of PAHs that everyone is exposed to every day. For example, on the topic of PAHs in food, the report quotes the World Health Organization as follows: “Food is a major source of intake of PAHs for the general population. Estimates of PAH intake from food vary widely, ranging from a few nanograms to a few micrograms per person per day. Sources of PAHs in the diet include barbecued/grilled/broiled and smoke-cured meats; roasted, baked and fried foods (high temperature heat processing); breads, cereals and grains (at least in part from gas/flame drying of grains); and vegetables grown in contaminated soils or with surface contamination from atmospheric fall-out of PAHs…

The point is that PAHs can accumulate in house dust because of every day living (for example, cooking or smoking or smoky fireplaces)or because of products that might contain PAHs (such as flooring glues or coatings or lubricants). And scientists have studied whether people exposed to contaminants via house dust have evidence of those contaminants in their bodies. Results of such studies so far seems to indicate that no, body burdens of people exposed to contaminants via house dust are not significantly elevated relative to those who are not exposed in this way.

People have been “making” – and been exposed to – PAHs since fire was invented. The USGS research team has tried to tie risks related to PAHs in house dust to pavement sealer. See the risk assessment peer review report for an evaluation of how that worked out for the USGS as a matter of science. In its continued advocacy campaign, the press has picked up on the USGS scare tactics, with over-the-top headlines. Via a third DQA Request for Corrections, has documented the exaggerations and unexplained deviations from risk assessment practices used by the USGS and their colleague at Baylor University in their assessment.

What about Exposure to PAHs in Air?

The USGS team has been busy – sediment, house dust, quantitative risk assessments, volatilizaiton into air. It’s unbelievable that two hydrologists can be experts in so many areas of science! asked scientists with expertise to evaluate the USGS volatilization studies. The review is available here. The reviewers found, to quote from their report, Based on our analysis, we find that the two papers recently published by Van Metre and coworkers (2012) overstate the volatilization of PAHs from coal tar sealers. These papers employ a set of modeling assumptions and experimental study design approaches that consistently bias their findings to overestimate PAH volatilization from sealed parking lots. By now, is not surprised to learn that the USGS team exaggerates. Sigh! A DQA challenge focused on the volatilization study is in the works.

What about those poor fish the USGS keeps showing us?

The USGS research team that is focused on RTS are trying to put a thumb on the scale of scientific evidence in an effort to advance their agenda. By using the photographs of catfish with horrible skin tumors in their presentations, the USGS is once again letting their agenda trump accurate science. This link is to a report by the US Fish & Wildlife Service scientist who is the source of those photographs. In the report, it is explained that the skin tumors on the catfish are not related to PAHs. Use of the fish photographs is, pure and simple, a scare tactic.’s second DQA challenge demands that the USGS stop using these inaccurate and misleading photographs.

Useful Information

Get the facts about how chemistry and chemicals have improved our lives at

A Position Statement of The American Council on Science and Health: Scared to Death: How Chemophobia Threatens Public Health

An article by Mark Lorch, Senior Lecturer in Biological Chemistry at the University of Hull in England: Five myths about the chemicals you breathe, eat and drink

A quick guide to understanding low concentrations of chemicals: Putting terms such as “ppm,” “ppb” and “ppt” into perspective