The second claim is this: "I've heard it causes cancer. Is this true?
The short answer here is that we have strong evidence that it would, but there is more work to be done.
Since the first study of any kind related to cancer risk and exposure to coal tar sealers is less than 5 years old, our understanding is just beginning. However, consider the following statement from the only toxicologist to study this in detail:
"The increased cancer risk associated with coal-tar-sealed asphalt (CSA) likely affects a large number of people in the U.S. Our results indicate that the presence of coal-tar-based pavement sealants is associated with significant increases in estimated excess lifetime cancer risk for nearby residents," said E. Spencer Williams, Ph.D., principal author of the study and Baylor University assistant research scientist at the Center for Reservoir and Aquatic Systems Research in Baylor's College of Arts & Sciences.
Supporting statement #1: OSHA, IARC or the EPA haven't classified coal tar sealers as hazardous.
The logic here is flawed. These institutions haven't classified coal tar sealcoat as hazardous, but neither have they concluded it is safe. This is called an "argument from ignorance" in logic. Just because you haven't tested a theory, doesn't make it false. In none of these situations have pavement sealers been evaluated. This is the logical equivalent of a teenager saying, "well my parents didn't say I couldn't go into that bar."
But they have classified one of the main ingredients, coal tar pitch, a "known human carcinogen." Not sure what the lawyers would say but something that is 35% a known human carcinogen isn't exactly as pure as the driven snow.
Supporting statement #2: "No evidence of cancer risk increase"
Not sure where they came up with the statement that the people working in distillation plants have no increase in cancer risk. The National Institutes of Health says quite the opposite:
A previous Working Group (IARC, 2010) concluded that there was sufficient evidence in humans for the carcinogenicity of occupational exposures during coal-tar distillation.
That link goes on to describe studies where the cancer risk does go up for these workers.
Supporting statement #3: Hazardous claims are just hype based upon poor scientific data
In January 2016 the EPA supported the findings of the USGS on coal tar pavement sealers.
One of the long-standing positions by industry is that the USGS research is flawed. However US EPA agreed that the "quality, objectivity, and transparency is sufficient for their intended uses. EPA is therefore retaining the references to the studies in its publications."
In addition, studies have been performed which independently agree there are toxicity problems with coal tar pavement sealers.
Supporting statement #4: It is impossible to know the risk because individual PAHs don't exist in the environment
This is what is known as a red-herring: a distracting statement which attempts to prove a statement no one is making. One of the main ingredients in coal tar sealers is coal tar pitch, which is a known human carcinogen. No one is saying it is on the basis of some individual PAH that makes it a carcinogen. It is the mixture in total.
That isn't something new either. The first laboratory generated cancers were accomplished by rubbing coal tar on rabbits ears about 100 years ago. The risk that was generated by the Baylor University study is theoretical, but based upon established means and methods in the field of toxicology. There is nothing technological standing in the way of additional studies and furthering our understanding of the risk of coal tar sealers.
So we can't yet characterize the cancer risk associated with coal tar pavement sealers based upon actual analysis of the population, but a professional toxicologist believes that a number of Americans are already affected by this product.
Knowing this is it reasonable to continue to use it where your children play?