HomeMy WebLinkAboutPAH proposalItem 11
Decreasing the PAH Content of Urban Runoff
Polycyclic Aromatic Hydrocarbons (PAH) are a class of chemicals that have been shown to
accumulate in the sediments of our lakes and streams. PAHs are generally insoluble in
water and tend to be strongly adsorbed to the fine particulates that are carried in our storm
water runoff. Numerous studies have shown PAHs to be toxic to various aquatic species and
some are also suspected human carcinogens.
The simple organisms that live in the lake sediments are at the base of the food chain. Fish
and other organisms higher in the food chain can be expected to concentrate toxins found in
the sediments. Bioaccumulation of PCBs is but one example. Animal studies have shown
increased instances of skin, lung, bladder, liver, and stomach cancers from prolonged PAH
exposure. Animal studies have also linked PAH exposure to birth defects and difficulty in
reproducing.
In 2006 a study by the city of Austin, TX and the US Geological Survey found that asphalt
parking lots that had been seal coated with coal tar based sealants were a major contributor
to the PAH concentration in the runoff to their rivers and streams. Coal tar is a byproduct of
the coking process and it has a PAH concentration of 50% or greater by weight. The fine
particulates that had abraded from parking lot surfaces that had been sealed with coal tar
sealants were found to contain an average PAH concentration of 3500 mg /kg compared to
only 54 mg /kg in the particulates abraded from the surfaces of unsealed parking lots. The
abraded particulates from parking lots that had been seal coated with asphalt based sealants
had a PAH concentration of about 620 mg /kg. Clearly, both types of sealants caused
increased PAH contamination in the runoff from parking lots but coal tar based sealants
resulted in much higher contamination.
Austin, TX found the study to be compelling enough to ban the sale and use of coal tar
based sealants. Similar bans have been proposed or implemented in other locations through-
out the US. A state wide ban is being proposed in Minnesota; Washington, DC has banned
these materials, and Massachusetts has restricted their use near wetlands. In our own state,
Dane County has instituted a ban on the sale and application of coal tar based sealants.
Dane County's ordinance in fact bans both phosphate in lawn fertilizers and coal tar based
sealants since they consider both to be detrimental to the health of their watershed.
Since Oshkosh is located next to Lake Winnebago, one of the largest inland lakes in the
country, and its health is of vital importance the issue of PAH contamination needs to be
addressed. While the PAH load to urban runoff can be reduced through a variety of best
management practices such as frequent street sweeping the city should also consider
reducing or banning the use of coal tar based sealants on parking lots and residential
driveways. By reducing or eliminating these sealants we can have a direct impact on the
PAH load carried by storm water runoff.