While this shouldn’t be surprising to anyone who has smelled the stuff when it’s being applied, coal-tar-based sealants used on pavement are the primary source of toxic polycyclic aromatic hydrocarbons (PAHs) in streambed sediments in Milwaukee, Wisconsin, according to a new study from the US Geological Survey and the Milwaukee Metropolitan Sewerage District.
The findings, of course, very likely apply to many other regions as well, pretty much anywhere that coal-tar-based sealants are used extensively on pavement.
For those unfamiliar with the terminology being used, just think of that really dark black (at least initially) covering that you see on some parking lots, playgrounds, and driveways — that’s pavement treated with coal-tar-based sealants.
As the name implies, the sealant is made from “coal tar,” which is itself a human carcinogen (despite its regular use on playground pavement). It also contains high levels of PAHs, some of which are highly toxic to aquatic life and also to humans.
Here’s more from the press release:
“Scientists with the USGS collected sediment samples from 40 streambed sites and dust samples from six parking lot sites in the Milwaukee area to determine the likely sources and toxicity of PAHs in streams. They found that dust from coal-tar-sealant contributed about 42% to 94% of the PAHs to the samples, with the remainder of PAHs coming from sources such as coal combustion and vehicle emissions.
“78% of the sediment samples collected had PAH levels that could adversely affect aquatic organisms like aquatic insects. Among the most toxic samples collected were those from sections of Lincoln Creek, Underwood Creek and the West Milwaukee Ditch.”
Commenting on the findings, lead author and USGS scientist Austin Baldwin stated: “This study shows that PAHs pose a very real threat to aquatic organisms at the base of the food chain. In terms of toxicity to these organisms, PAHs are probably the most important contaminants in Milwaukee-area streams.”
What Baldwin means when he says “toxicity” is liver failure, fin erosion, immune system impairment, and cataract formation. Not minor health problems — rather major ones.
Baldwin continued: “Our study did not test the human health effects of coal-tar-sealant or PAHs in the Milwaukee area. PAHs do not easily accumulate within the food chain, so possible human-health risks associated with consumption of fish are low.”
Obviously, though, since the coal-tar sealants are used directly on parking lots, playgrounds, and driveways, people are directly exposed. The most common route of exposure would likely be dust contamination and inhalation.
Those interested in reading the full study can find it here.
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