Asbestos fibers: barking up a tree.

In Libby, Mont., mining of asbestos-contaminated vermiculite--a natural insulating material--sickened or killed many workers and townspeople in recent decades. Now, a study finds that even 16 years after the vermiculite mine closed, area trees hold substantial amounts of asbestos, rendering them hazardous to a separate group of workers.

Logging is a major employer for people around Libby. With asbestos a potential contaminant in dust, Tony J. Ward of the University of Montana in Missoula and his colleagues wondered whether asbestos from the mining operations might have settled on local trees.

Ward, an atmospheric chemist, notes that his team found between 40 million and 530 million asbestos fibers per gram of bark on trees within 4 miles of the mine--"concentrations that are pretty staggering" Even 15 miles from the mine, but near a railway siding where trains took on vermiculite, tree bark holds up to 19 million fibers per gram, his team reports in an upcoming issue of Science of the Total Environment.

Not only loggers but also locals who cut and burn wood for home heating face a risk from the fibers, Ward worries. He and his colleagues say that the findings also suggest that people who live far away from Libby but along former transportation routes for the vermiculite might face a health threat.--J.R.