MINNEAPOLIS (AP) — Seven Minnesota cities are suing a group of companies that refine coal-tar sealants to help pay for cleanup after the product's harmful chemicals ended up in stormwater ponds across the state.

The cities filed separate federal lawsuits last month to try to hold the companies accountable for the products used by Minnesota residents to seal driveways and parking lots for years.

Attorney Robin Greenwald represents the seven cities. He says cities facing the costly cleanup have to either burden taxpayers or the polluters to pay for the removal of contaminated material from stormwater ponds.

Minnesota banned sealants made from refined coal tar in 2014 as concern grew over the presence of polycyclic aromatic hydrocarbons in the environment. Some of the chemicals are known to cause cancer in humans.