(Chesapeake Bay Foundation photo).
By Harry Campbell
Summer is coming. As trees and plants have emerged from their winter slumber, so have outdoor projects for Pennsylvania homeowners. What many don’t realize is that one of those tasks, sealing driveways and parking lots, can pose significant risks both to human health and to aquatic life in our rivers and streams.
Sealants are marketed as a way to help maintain blacktop on driveways and parking lots. Although formulations of many available products vary, they all are intended to help keep the ravages of rain and snowmelt from forming and worsening cracks in paving, which can ultimately reduce the lifespan of macadam. Many products, whether do-it-yourself and professional grade, use coal and oil tars as the main active ingredients.
Tars have hundreds of compounds, including a class of water repelling ones collectively called polycyclic aromatic hydrocarbons (PAHs).
Studies have found that PAHs increase the risk of lung, bladder, and skin cancers in humans, pets, and developmental delays in children. According to a study in the journal Environmental Science and Technology, people living near pavement sealed with coal tar have an elevated risk of cancer.
Humans and our furry friends are exposed to the coal tar sealant chemicals by walking on the surfaces and breathing in volatilized compounds. It has been documented that small children are most vulnerable, as they put their hands in their mouths and tend to get down on the ground.
The chemicals get into our houses and yards too. One study found that residences next to parking lots with coal tar-based sealcoat had PAH levels in house dust that was 25 times higher than residences adjacent to unsealed pavement.
When these chemicals get into rivers and streams, they can form a toxic brew for sensitive critters. One study found that runoff from areas with seal-coated pavement was acutely toxic to minnows and small water bugs. Researchers found that the PAHs in the runoff damaged the DNA of critters. Another study found that 100 percent of critters exposed to runoff from pavement sealed with coal tar products died within 42 days. Runoff from uncoated areas had mortality rates of less than 10 percent.
The toxic effects are long-term as well. In fish populations, PAHs in runoff have been found to cause lesions, liver abnormalities, tumors, and decreased juvenile growth. A study in Washington State tested runoff from coal tar-sealed pavement on juvenile salmon. Even after seven months, runoff from sealed areas killed 55 percent of juvenile salmon within 96 hours. Studies have found similar results in other species.
PAHs also tend to store in sediment, making them particularly troublesome for animals that live part of their lives in the mud or streambeds or eat critters that do, like many frogs, fish and salamanders. PAHs have even been found in young dragonflies.
Continued exposure to PAHs leads to concentrated levels inside the body, a process called bioaccumulation.
So concerning is the science on coal tar sealants that 12 states and Washington, D.C. have enacted bans on their sale and 17 have restrictions on use. Pennsylvania, and its multitude of local governments, are not among them.
The best way to reduce your exposure to coal tar sealant chemicals would be to have them removed from Pennsylvania stores. The next best thing is not to use them. Many homeowners have replaced asphalt with concrete or, even better, permeable pavers.
If you have to use a sealant, similarly priced alternatives that are just as effective are readily available. Asphalt-based sealcoats have less PAHs than coal tar. It will be better for your family’s health, your pets, and the health of our fish and wildlife.
Harry Campbell is Science Policy and Advocacy Director of the Chesapeake Bay Foundation in Pennsylvania.
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