Another Maryland county has made it illegal to use coal tar pavement products that are known to contribute pollutants to area streams and the Chesapeake Bay, becoming the third municipality in the region to do so.

Prince George’s County joined the District of Columbia and Montgomery County, MD, when its ban of coal tar pavements went into effect at the beginning of July. This category of thick brown or black liquid is a byproduct of the carbonization of coal that has been used for decades to seal driveways, parking lots, playgrounds and recreational trails to extend the life of asphalt and concrete surfaces.

But mounting evidence shows that these products, to which there are alternatives, contribute toxic chemicals that persist in waterways and harm human and wildlife health. The coal tar products contain high levels of polycyclic aromatic hydrocarbons (PAHs) that are toxic to fish and cause cancer in humans.

A study in the April issue of the journal Environmental Science showed runoff from coal tar-sealed pavement remained deathly toxic to minnows and water fleas (which make up the base of the food chain) in rainwater runoff as long as three months after coal tar sealant was applied.

“With more and more clear science connecting coal tar sealants to serious public health and environmental damage, bans on the use of coal tar as a pavement sealant should be considered Baywide,” said Dan Smith, public policy and advocacy director for the Anacostia Watershed Society, which lobbied for the ban in Prince George’s County.

For now, Smith’s group is celebrating the ban in Prince George’s that should help prevent the future use of coal tar sealants in the entire 176-square-mile watershed of the Anacostia River. As of July 1, it is illegal to sell, use or permit the use of these sealants, which are no longer sold at Home Depot or Lowe’s stores nationwide. In Prince George’s County, property owners are subject to a fine of $1,000 per day per violation.

Residents of Montgomery County have faced the same fine since December 2012, when that jurisdiction banned coal tar sealants.

In DC, where coal tar sealants have been banned since July 2009, the daily fine for violations is $2,500.

The district also has a tip line that residents can call to report suspected violations of the ban. The District Department of the Environment began in 2014 remediating more than a dozen sites contaminated with coal tar pavement.

“The remediated sealant from these 13 sites contained the same amount of PAHs as approximately 600,000 gallons of undiluted used motor oil, the third most concentrated source of PAHs in the urban environment,” the DDOE website states.

Annapolis’ City Council also has considered a ban on coal tar sealants, but it was not successful.

Fred Pinkney, toxicologist with the Chesapeake Bay Field Office at U.S. Fish and Wildlife Service, said it’s difficult to know how widely PAHs are used in the Bay watershed. Coal tar sealants are more widely used east of the Mississippi River and less toxic asphalt sealants are largely used in the West, he said.

The U.S. Geological Survey has conducted most of its research on the substances out of Austin, TX, which was one of the first municipalities to ban the sealants. Washington and Minnesota have statewide bans on the coal tar products, and cities in two dozen states have some form of ban or restriction on the products, according to the advocacy group Coal Tar Free America.

Coal tar sealant often requires reapplication every two to five years where tires and snowplows reduce the coating to a fine dust. The dust, which contains high concentrations of PAHs, can be blown, washed or tracked into nearby soil and waterways and can persist for years after application, according to research by the USGS.

According to their research, people living next to coal tar-sealed pavement are 38 times more likely to get cancer during their lifetime and are at a greater risk if they lived there during early childhood.

Most of the research about its specific impact on wildlife is linked to what scientists know about PAHs and other toxics, but they agree more studies — such as the one released in April about minnows and water fleas — are needed.

As for the Bay watershed, a USGS sample at Lake Anne in Reston, VA, found more than 80 percent of the PAHs in sediment were likely deposited from coal tar sealants.

The Chesapeake Bay Program’s toxic contaminants workgroup is working to prioritize which toxics present the most harm to the waters and wildlife of the Bay and should be tackled first.