A preliminary study of the effect of calcium chloride highway anti-icer liquid on roadside trees in Leavenworth, Washington

by Dirkse, Jason Lennart.

By Jason Lennart Dirkse Washington State University May 2006 Chair: Eldon Franz Recently observed foliar injury of trees along roads in and around Leavenworth, Washington, has elicited concern as to the cause of the injury. Leaves of certain trees, most noticeably big-leaf maple (Acer macrophullym), become browned, dried, and curled in early summer. However, these symptoms are only seen along certain stretches of certain roads, most severely along a 7-mile portion of State Highway 2 west from Leavenworth, and along the first ~4 miles of Icicle Road near Leavenworth. While the symptoms look similar to those of drought conditions, drought cannot sufficiently explain the limited and specific geographic distribution of the observed symptoms. A survey of relevant scientific literature reveals that highway anti-icer liquids applied to prevent ice build-up can have a similar effect on roadside trees as that which is observed. This explanation would more adequately explain the observations, and upon further investigation, there are a number of compelling reasons to suspect anti-icers as the cause of the observed injury symptoms. This study investigates the effect of highway anti-icers iv (specifically calcium chloride) on trees when added to the soil in which the tree is growing. Tree saplings were grown in a greenhouse, divided into five treatment groups, each containing three individuals of four species—black cottonwood, Douglas fir (Pseudotsuga menziesii), big-leaf maple (Acer macrophyllum), and Ponderosa pine (Pinus ponderosa)—for a total of 12 trees per treatment group. Each treatment group was given a different concentration of anti-icer liquid diluted with deionized water, added to the soil, once weekly for eight weeks. Growth was monitored both during and at the conclusion of the experimental period to determine if different concentrations of anti-icer resulted in different growth rates among the treatment groups. It was found that the anti-icer treatments caused significant injury to the trees, producing leaf browning and die-back, and likely killed all trees except the control group. Further study of this topic is warranted, as this study provided reason to suspect that highway anti-icers can cause significant damage to trees growing in the soil to which the anti-icer is added. v