The study, by Xinghua Qui and Ronald A. Hites of the IU School of Public and Environmental Affairs, was published by the journal Environmental Science & Technology. The study demonstrates that tree bark can be used as nature’s own passive sampling device for detecting the presence and relative concentrations of chemicals in the air. Rough, porous and high in lipids, tree bark soaks up airborne gases and particles, then keeps them protected from the elements.

“It’s really a very convenient technique,” Hites said. The sampling doesn’t hurt the tree, and “you get an integrated measurement of what the tree has been exposed to over the last few years.”

Concentrations in tree bark within a few miles of the factory were several thousand times higher than those found in bark at more distant sampling sites, including Indiana, Virginia and Maryland. Dechlorane Plus has been used for more than 40 years as a flame retardant in electrical cables and wiring, and other products, but little data is available on its toxicity, according to an Environmental Science & Technology article. One of more than 175 types of flame retardants, it was developed as a substitute for the banned, highly chlorinated flame retardant Dechlorane (also known as the insecticide Mirex).