Unwanted Traveler Settles in Alaska Trees
Being the wonderful place it is, Alaska attracts migrants of all shapes and forms--from ducks winging their way north in the springtime to humans towing both trailers and dreams of life in the Last Frontier. Because of its location on the globe, Alaska also draws its share of wind-carried pollutants from other areas of the earth.
In a recent study by Indiana University researchers, samples of Alaska tree bark showed high concentrations of pesticides that were sprayed on crops possibly half a world way. The Alaska results were part of a worldwide analysis of tree bark performed by Ronald Hites, a chemistry professor at IU in Bloomington, Indiana, and Staci Simonich, who earned her doctorate degree with the research and now works with Proctor and Gamble in Cincinnati.
Northern areas such as Alaska become home to pesticides hitching a ride on the wind because of what Simonich calls a "global distillation process," where airborne pollutants are carried from warm to cold areas. Once in a cold area, they settle on vegetation, soil and bodies of water.
Picture it this way: a farmer growing rice in India sprays his crop with an insecticide, some of which misses the mark and floats in the air. The wind picks up the chemical particles and carries them northward. When the particles collide with cold air over northern parts of the globe, they change from a gas to a liquid and settle out in a new home. Hites likens this condensation process to the steam from a coffee cup set on the dashboard of a cold car. The steam rises until it hits the cool surface of the windshield; there it reverts back to a liquid as an annoying foggy patch on the glass.
Tree bark provides a unique landing pad for condensed pesticides. Tree bark contains fats, called lipids, which help create a waxy coat that prevents the tree from losing too much moisture during dry periods. These lipids act as a magnet for the condensed insecticides.
With the help of friends and colleagues, Hites and Simonich collected 200 tree bark samples from all over the world. Simonich asked a friend who worked in the lab and was traveling to Alaska to gather a few samples. The bark fragments, some collected from a variety of tree species near Denali National Park, showed a high level of lindane. Lindane is the active ingredient in pesticides used to kill aphids and other insects that plague agricultural operations varying from tree plantations to rice farms.
Simonich said the level of lindane found in Alaska tree bark isn't high enough to harm people, wildlife, or trees, but it is a good indicator of how far pollutants can travel. She said the lindane found in Alaska tree bark could have originated from local sources--although it's not likely due to the scarcity of Alaska farms and tree plantations--or from as far away as India.
In the study, published in the Sept. 29 issue of Science, Hites and Simonich found high lindane concentrations in tree bark from other high-latitude countries such as Norway, Canada, Sweden, Scotland and Russia. Simonich said the bark samples from Norway were gathered from a particularly remote site, which buttresses the theory that lindane--a chemical that easily changes from gas to liquid--travels on the wind toward the cold regions of the globe.
Simonich said the tree bark actually cleans the air of such compounds, but the fate of pollutants after trees die and bark decays isn't as clear. In a sense, Alaska trees could be cleaning the earth's atmosphere by collecting the remnants of pesticides sprayed on the other side of the globe.
