Coal tar pavement sealers are much more toxic than we thought


HRWC has been advocating for the elimination of coal tar sealcoating in our watershed. This is a widely used asphalt maintenance practice in our area and coal tar sealcoats have very high levels of PAHs, many of which are known to be harmful to aquatic life and people.

New research has found that previous studies have, if anything, underestimated the toxicity of coal tar sealcoats. Researchers at Oregon State University investigated the toxicity of both coal tar and asphalt based sealcoats. Unique to this study, a much larger number of PAHs were analyzed.  Researchers also assessed toxicity to zebrafish.

When a larger number of PAHs found in sealcoats were included, the indicator for carcinogenicity was 4-39% higher than had been found in previous studies.* Asphalt-based sealcoats, while still toxic, were found to be far less toxic than their coal tar counterparts.

We recommend residents, businesses and other property owners choose asphalt-based sealcoat or abstain from sealcoating altogether when considering options for asphalt pavement maintenance. The risk to our environment and communities is too high and the evidence is mounting.  Learn more at


*range represents the results from two coal tar products and whether the carcinogenicity was determined using USEPA or Health Canada standards, which are more stringent.