Lichens, combinations of fungi and algae, are quietly trodden underfoot by animals and hikers the world over. Now a new study by a Brigham Young University father-son team has demonstrated that lichens could replace expensive environmental monitors since they accumulate some pollutants in concentrations that correctly manifest the amount of the pollutants in the surrounding air.
"Previously, we knew that lichens took things up from the air, but no one had any significant results indicating that what is in the lichen accurately reflects what is in the air," said Larry St. Clair, the chair of BYU's department of integrative biology and co-author of the study published in the latest issue of "Atmospheric Environment." "This is the first definitive data that shows not only do lichens take pollution up from the air, but they take it up in patterns that exactly reflect the amount of pollutants in the air."
Lacking roots, stems and leaves, lichens can grow almost anywhere, but rely on nutrients they accumulate from the air. Thus, they are uniquely sensitive to air pollution, making them valuable as early warning indicators of reduced air quality. Scientists have used them as biomonitors for decades, including an effort to estimate the amount of nuclear fallout from the Chernobyl melt down in the late 1980s.
Since St. Clair's son Sam was 6 years old, he has helped his father gather lichen samples from more than 400 sites in the U.S.'s Mountain West from Mexico to Canada. For the new study, the duo focused on lichens collected at Chiricahua National Monument in southeastern Arizona for part of Sam's graduate work in botany at BYU.
Noting significant copper smelting activity in the area, the researchers took advantage of bi-weekly mechanical measurement of copper levels in the ambient air between 1994 and 1998 conducted by scientists at University of California, Davis. The St. Clair pair recorded the levels of copper absorbed by lichens collected at selected sites in the Monument and compared the results to those generated by the machines. The concentration of copper in the lichens reflected the concentration of copper in the air.
"If such relationships are found to be robust in further studies, it would mean that we would be able to predict air quality status by collecting lichen samples and determining their elemental content," said Sam St. Clair, now pursuing a Ph. D. at Pennsylvania State University. "Air quality status could therefore be quantified wherever lichens are present."
Using lichens would eliminate the need for installation and maintenance of expensive and immobile air sampling equipment that collects airborne particulates using filters, which are later removed and analyzed in a lab.
"In essence the lichen tissue appears to functions like a natural filter, accumulating airborne pollutants as they are deposited on the lichen surface," Sam St. Clair said.
The technique for analyzing pollutant elements on a filter or in lichen tissue is the same.
The St. Clairs' paper was co-authored by BYU professors Nolan F. Mangelson and Darrell J. Weber.