Swamp Stomp
Volume 17, Issue 11
According to a study conducted by the U.S. Geological Survey and the Milwaukee Metropolitan Sewerage District, coal-tar sealants which are used on blacktop parking lots and driveways are the primary source of toxic chemicals found in the muck at the bottom of area waterways.
The study tested muck samples that were collected from 40 locations along 19 creeks and rivers in the metropolitan area of Milwaukee and dust from six parking lots. It found that coal-tar sealants contributed up to 94% of all polycyclic aromatic hydrocarbons, or PAHs, in streambed sediment, according to the study, which was published Thursday December 22, 2016 in the journal Environmental Toxicology and Chemistry.
Of all of the samples, a total of 78% of them contained enough PAHs to be considered toxic and capable of causing adverse effects in aquatic animals, said Austin Baldwin, a USGS scientist and lead author of the study. The sample location which had the most toxic sediment came from Lincoln Creek and Underwood Creek.
PAHS gets into the streams when rain and melting snow rinse it and other contaminants off the pavement and into storm water storage basins or directly into storm sewers that carry the load to waterways.
“Even before the study was published, early circulation of its findings boosted support for local restrictions or even bans on the use of coal-tar sealants and a switch to sealants containing asphalt emulsions,” according to Chris Magruder, a retired Milwaukee sewer district scientist who is science advisory committee coordinator for the Southeastern Wisconsin Watersheds Trust.
A previous federal study conducted in 2013 determined that PAHs posed a greater risk of harm to aquatic life in the streams than other chemicals but this study went beyond the previous study in two ways, Baldwin said.
The first was that researchers used multiple methods for identifying separate sources of PAHs in sediment, he said. Apart from coal-tar sealants, the remainder of the PAHs came from a variety of other sources, such as coal combustion at power plants and vehicle emissions.
The second was that this study exposed aquatic insects and small crustaceans to sediment taken from streams in the area.
“This study shows that PAHs pose a very real threat to aquatic organisms at the base of the food chain,” he said. Some of the adverse effects are fin erosion, liver abnormalities, cataracts and immune system damage. Additionally, exposure to the chemicals can cause high rates of tumors in fish.
“The study also reveals a costly consequence of regulations in Wisconsin and many other states requiring developers to excavate storm water storage basins next to massive parking lots. PAHs cling to dirt, sand and other particles in the storm water that settle to the bottom of the basins” (Behm).
It has been estimated by communities in the Minneapolis-St. Paul metropolitan area that it will cost up to $1 billion to dispose of PAH-contaminated sediment in the storm water ponds when the basins are dredged for maintenance.
Source: Behm, Don. “Some Driveway Sealants Create Toxic Muck in Streams.” USA Today. Gannett Satellite Information Network, 26 Dec. 2016. Web. 10 Feb. 2017.