New Research Highlights Problems with Biocides in Some Sealcoats

Going to print this month is research out of Dickinson College (PA) about the potential leaching of biocides out of some asphalt-based pavement sealers. The research is already online in the peer-reviewed, science periodical Science of the Total Environment at this link:

The study analyzed simulated runoff from freshly applied, but cured asphalt-based sealer from 3 separate products. All were purchased at home improvement stores.

The author, Dr. Amy Witter, has tracked and tested the effects of high PAH sealcoats in previous papers.

The results found that 2 of the 3 asphalt sealers had runoff concentrations of biocide high enough to significantly effect a common water quality indicator bug (water flea) when the runoff was more concentrated than a 1 to 8 ratio.

These particular biocides, according to the author, are “are meant to protect product during storage.”

Other chemicals were found leaching from the sealcoats, but none were nearly as problematic as biocides.

Some bulk sealer manufacturers state that biocides are not used in their products because they have a much reduced storage time and no need for them. It is unknown the extent of their use at this time. A more thorough investigation of the use of these products across the entire asphalt sealcoating industry is warranted.

Are these typically just used for retail packaging and storage and not used by larger commercial bulk manufacturers? Do you manufacturers use them? If so, when?

To be specific, the biocide is often referred to as isothiazolinone biocides or CMIT/MIT (Σ 5chloro-2-methyl-3(2H)-isothiazolinone / 2-methyl-4-isothiazolon-3-one). They have been used in shampoo, skin care products and cosmetics. Because of allergic reactions, one article stated that CMIT is no longer allowed on “leave on” products.

While we aren’t trying to ignore these findings, it is important to put them into perspective. How do these toxicities compare to those of high PAH sealers? While both have an safety data sheets with the signal word “Danger” and numerous hazard statements, biocides are NOT a necessary ingredient to asphalt-based pavement sealers, but for high PAH products they are the main ingredient in the product. Big difference.