That question was answered long ago and has been nearly forgotten. Nearly 100 years ago, scientists were mystified at what exactly caused cancer. Some thought it was parasites or bacteria; others thought it might be from repeated exposure to harmful chemicals, but no one knew for sure. Until some Japanese researchers decided to put their chemical exposure theory to the test.
In 1915 Drs. Koichi Ichikawa and Katsusaburo Yamagiwa of the Hokkaido University, Japan painted coal tar on the ears of 101 rabbits every 2 or 3 days. They designed their experiment because of the common knowledge that boys who were chimney sweeps developed cancers from exposure to tar build-up on the inside of chimneys. Abnormal growths were seen on the rabbit ears in just 30 to 100 days. After 150 days, 100% of the rabbits developed cancer.
For this discovery, the first of its kind, Ichikawa and Katsusaburo were nominated for a Nobel Prize, which would have been Japan's first. Ironically they lost out to a Danish researcher who had compelling evidence that stomach cancers were caused by parasites, which was later proven to be false.
How does this relate to coal tar sealants? While coal tar sealants have some rather inert substances added to them, research has shown the following:
- coal tar sealants, like coal tar, are potent mutagens (Just How Toxic are Coal Tar Sealants?")
- coal tar sealants, like coal tar, contain human carcinogens. (National Institutes of Health says: "Coal tars and coal-tar pitches are known to be human carcinogens based on sufficient evidence of carcinogenicity from studies in humans.http://ntp.niehs.nih.gov/ntp/roc/twelfth/profiles/CoalTars.pdf
- Cancer Risks Shown "Significant" For Children Near Coal Tar Sealant Dust/Dirt
- the toxic portion of coal tar, PAHs (polycyclic aromatic hydrocarbons) are about 25% less in coal tar sealants than in a standard coal tar solution. Purity of Refined Coal Tar
Now if only we all had a briar patch to keep coal tar sealants from affecting us as well or maybe we should just stop using them altogether.
For more on the rabbit research see the following sources:
and the original research paper (in English)