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Pavement Sealcoat Major Pollutant in U.S. Lakes, Reports Study

Commentary by LASN editor Stephen Kelly

PHPs (polycyclic aromatic hydrocarbons), found in coal-tar pavement sealcoats, have been known as probable human carcinogens since the 19th century when chimney sweeps plied their trade. I cringe looking at this photo, as when I seal-coated asphalt back in the early 1970s, I didn't have a mask.
Rain bird
Teak Warehouse Came America

In my college days, I used to earn extra money by helping my friend Duane complete construction jobs he'd bid on and won. I was "the crew." Some of that work was asphalting and sealing. One job stands out: a large church parking lot we asphalted and sealed in 100 plus degree heat in Fresno, Calif. I recall this job not only because of the miserable conditions and breathing in those toxic fumes, but for helping a man to a nearby hospital who had been beaten with a baseball bat. Duane didn't want to "get involved." Oh, and one of my contacts popped out of my eye and was lost in the sealer (replacement cost about what I earned for the week's work).

I bring up my short-lived asphalting career because of a recent U.S. Geological study, "Contribution of PAHs from coal-tar pavement sealcoat and other sources to 40 U.S. lakes" (Science of the Total Environment, Volume 409, Issue 2, 15 December 2010, pages 334-344, Peter Van Metre, Barbara J. Mahler).

The study's abstract notes contamination of urban lakes and streams by polycyclic aromatic hydrocarbons (PAHs) has increased in the U.S. during the past 40 years. However, it's only been in the past five years that Van Metre and other scientists have pinpointed the commonly used coal-tar-based sealant as a major source of PAHs in urban lakes. He and other scientists reported in 2005 that runoff from parking lots with coal-tar-based sealant was a major source of PAHs in Austin streams.

The researchers evaluated sources of PAHs in post-1990 sediments in cores from 40 lakes in urban areas across the U.S. Anchorage, Alaska; Fort Worth, Texas; Portland, Ore.; Seattle; Orlando, Fla.; Raleigh, N.C., Chicago, Newark, N.J., Detroit; Milwaukee and Boston were among the cities where lake waters were tested.

All the best modeling scenarios "indicate CT sealcoat is the largest PAH source when averaged across all 40 lakes, contributing about one-half of PAH in sediment, followed by vehicle-related sources and coal combustion. PAH concentrations in the lakes were highly correlated with PAH loading from CT sealcoat."

Lakes with the higher levels of PAHs also had a large fraction of the PAHs coming from coal-tar-based sealants.

PAH concentrations from CT sealcoat were significantly greater in the central and eastern U.S. than in the western states, reflecting, the scientist said, regional differences in use of different sealcoat product types. "In seven of the 40 lakes, CT sealcoat has been the largest source of PAHs since the 1960s, and in six of those lakes PAH trends are upward.


Stephen Kelly, LASN editor

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November 22, 2019, 12:42 pm PDT

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