Moss growing on urban trees may revolutionize air pollution detection and regulation. Scientists recently discovered that moss harvested from hardwood trees in Portland, Ore., can be a useful bioindicator of cadmium air pollution.
The study, led by researchers from the U.S. Forest Service Pacific Northwest Research Station, is the first to use moss when creating a rigorous and detailed map of air pollution in a U.S. city.
"What's unique about this study is that we used moss to track down previously unknown pollution sources in a complex urban environment with many possible sources," explained Sarah Jovan, a research lichenologist at the Portland station.
Moss lack roots, meaning that it absorbs water and necessary nutrients from the atmosphere, making it a good indicator of environmental health.
Researchers found that moss was a good bioindicator of cadmium - a heavy metal linked to cancer and kidney disease - and uncovered pollution "hotspots" in the city near two stained-glass factories.
"Our study shows that moss bioindicators have the potential to improve air quality monitoring by serving as a screening tool to help cities strategically place their air quality monitors," Jovan added. "The heavy metals analysis for moss costs us $50 per site, a low cost that makes it possible to sample extensively and flag hotspots for follow up instrumental monitoring."
The exploratory moss study was launched in 2013 and involves the work of Drexel University researchers. A total of 346 samples of Lyell's orthotrichum moss - a species that grows abundantly on the trunks and branches of hardwood trees across Portland - were collected along a randomized grid.
The researchers then spatially modeled the data to create a fine-scale map of cadmium concentrations throughout Portland. In response to their findings, a mobile air quality-monitoring instrument was placed near one of the two stained glass factory hotspots. This instrument recorded 24-hour readings over the course of nearly a month, revealing that cadmium concentrations in the air are 49 times higher than Oregon's state benchmark.
"Data from this monitor, along with three others that Department of Environmental Quality (DEQ) was operating at the time, helped us compare our moss data with actual concentrations measured in the air," Jovan said. "We got a very high correlation, suggesting that moss may be able to estimate cadmium levels in the air very accurately, but we acknowledge that four data points is a small sample from which to draw definitive conclusions."
The researchers are now producing basic maps of 22 metals and other elements measured in the moss samples to be published this summer. This will aid future studies of potential pollutants in cities.
Their study was recently published in the journal Science of The Total Environment.
