Once appropriate, the use is obsolete
The City did what good pollution investigators do. They did research. They talked to experts. They had conversations with multiple sections of the Environmental Protection Agency. They talked to the state health department. And they had extensive conversations with industry leaders about what they knew about their own products.
At that time, there were a lot of unknowns.
After the compilation of all those answers and conversations and performing peer-reviewed research* on amphibians, aquatic species and runoff from coal tar sealed parking lots, the City of Austin felt they had what they needed to pass the ban of coal tar containing pavement products: evidence that coal tar sealers negatively affect aquatic species and that coal tar washes off from sealed parking lot surfaces during rain events.
In 2005, one might've said at that the ban in Austin was based upon the need to protect aquatic species only. Any discussion of the effects on humans would've been "precautionary" because there were many unknowns about the fate and transport and effects of coal tar sealants on humans.
But that was 12 years ago and now we know a lot more.
Here's a book definition of precautionary principle:
When an activity raises threats of harm to the environment or human health, precautionary measures should be taken even if some cause and effect relationships are not fully established scientifically.What We Know Is Beyond Precautionary
As you can see from the following summary, many cause and effect relationships have been firmly and fully scientifically established.
Here's a summary of what we know about coal tar sealers:
- PAHs are increasing in urban lakes around this country.
- Coal tar pavement sealer has exceptionally high PAH concentrations.
- Coal tar sealers are mobile. That's why you reseal a parking lot every two to three years.
- The use of coal tar sealers is extensive. Many of the mapped watersheds have about 40% of the parking lots covered in coal tar sealers.
- PAHs in house dust were elevated because they were being tracked in from the coal tar sealed parking lots.
- Research has found that coal tar sealers are the largest contributor to urban lakes and is responsible for the increase in PAH in receiving lakes across the country.
- There are increased cancer risks from contaminated dust exposure from coal tar sealed parking lots.
- Austin saw a 58% reduction in PAH levels since its ban went into effect (2014).
- More PAHs enter the atmosphere from coal tar sealers than all road traffic in the US.
- The runoff from coal tar sealed parking lots is toxic days after a parking lot is sealed.
- Coal tar sealers cause "significant" DNA damage.
"Precautionary" is the way my colleagues and I at the City of Austin used to wonder about the effects of coal tar sealers on people. Now none of us need to wonder anymore.
*The peer reviewed research was performed with other researchers both at universities and the USGS.