Problems posed by the waste-settling ponds near coal-fired power plants were big news four years ago, when a spill in Tennessee sent millions of cubic yards of coal ash waste into the Emory River. The ash was laced with toxic chemicals, yet federal action to deal with the now-evident threat posed by the nation’s more than 1,000 coal ash impoundments has been slow in coming.

Now a study led by researchers at Duke University’s Nicholas School of the Environment adds to the urgency. After analyzing water samples from 11 lakes and rivers in North Carolina, scientists found, according to a Duke announcement, “high levels of arsenic, selenium and other toxic elements in coal ash effluents and in lakes and rivers located downstream from coal-fired power plants’ settling ponds.”

Much has been done to reduce pollution from the smokestacks of coal-fired power plants. But protecting public health calls for paying more attention to the residues from burning that coal, because it’s now clear that these power plants can be hazardous to both air and water quality.