A chemical used to melt ice on Washington roads is damaging tens of thousands of trees along the state's mountain passes. The de-icer, calcium chloride...

WENATCHEE — A chemical used to melt ice on Washington roads is damaging tens of thousands of trees along the state’s mountain passes.

The de-icer, calcium chloride, is a form of salt that temporarily damages some trees but doesn’t kill any, according to the state Department of Transportation. The phenomenon, needle browning, will be more evident in pine and fir through the passes this spring after a brutal winter.

However, Jim Hatfield, a forest pathologist with the Wenatchee-Okanogan National Forest, says some trees die from exposure to the de-icer. Hatfield said his agency hasn’t formally studied needle browning but looked into changes in trees near roads where de-icer started being used almost exclusively four years ago.

“I would definitely say it’s something we should be looking into more in depth,” Hatfield said.

Doug Pierce, environmental-operations manager with the Transportation Department, said calcium chloride can “burn” roadside trees but that damage is minimal and trees recover in the summer.

The department also says it tests for chlorides in soil and creeks near roads and has not found elevated levels. Annual precipitation, including melting snow, provides adequate dilution to prevent buildup, according to an October department publication on needle browning.

Earlier this year, wildlife officials were concerned that road salt and de-icer were disorienting finches and other small, seed-eating birds that ingest them as they peck for grit. That, in turn, made them roadkill when they were hit by snowplows and other vehicles during the winter.

The U.S. Forest Service is not studying the browning phenomenon and is not asking the Transportation Department to change its practices.