Lichens accurately measure air pollution

“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, Professor of Integrative Biology at the Brigham Young. Larry St Clair and his son, Sam, have now produced the first definitive data that shows that lichen takes up air pollution in patterns that exactly reflect the amount of pollutants present in the ambient air.

Sam has been helping his father collect lichens from more than 400 sites in the US’s Mountain West from Mexico to Canada since he was six years old. The lichens used in the latest study came from the Chiricahua National Monument in Arizona as part of Sam’s graduate work in botany at the university. He is now studying for a PhD at Pennsylvania State University.

The Chiricahua area is home to a significant amount of copper smelting, and was subject to bi-weekly mechanical measurement of copper levels in the air between 1994 and 1998 by scientists from the University of California. The St Clairs were able to compare the mechanically obtained readings with those from lichens.

The research involved two basic lichen growth forms, foliose and fruticose. The St Clairs are confident that any species from either group would produce accurate results for copper pollution. The next step in their research will be to compare the uptake of 15 to 20 common pollutant elements in the thalli of fruticose and foliose lichens.

“In essence the lichen tissue appears to function like a natural filter, accumulating airborne pollutants as they are deposited on the lichen surface,” said Sam St Clair. The technique for analysing pollutant elements on a man-made filter or in lichen tissue is the same.

“This potential would revolutionise the use of lichens as biomonitors of air quality and bioaccumulators of air pollutants by virtually eliminating the need for direct mechanical monitoring of concentrations of air contaminants in ambient air samples,” Larry St Clair told edie. Lichens can even be transplanted into sites impacted by air pollution.

The St Clairs usually collect two to three grams of lichen material at a time, making use of 100-200 micrograms for analysis, and archiving the rest for future reference. Currently, in the Herbarium of Non-vascular Cryptogams at Brigham Young University, for which Larry St Clair is the curator, there are 1,000 archived entries from more than 450 sites in the 10 western US states, dating from the 1970s.