Heavy metal pollution is of great concern across the globe due to the highly toxic nature of many metals and their prevalence in urban environments. Terrestrial epiphytic mosses can be used as biomonitors to inexpensively estimate atmospheric heavy metal concentrations. However, much remains unknown about the relationship between metal content in moss tissues and atmospheric concentration. Plant physiology and environmental conditions affect metal accumulation rates in moss tissues and can therefore determine the degree of variability among samples. A hierarchical sampling method was used to model spatial variation of heavy metal content in a terrestrial epiphytic moss, Orthotrichum lyellii. Four samples were collected from each of four trees at several sites in Oregon representing an unpolluted site, urban sites, and a polluted parkland site downwind of Portland. The moss was acid digested and analyzed for Pb, Cd, and Zn by inductively coupled plasma mass spectrometry (ICP-MS). The results indicate high variability among samples and among trees, especially at the polluted urban locations, emphasizing the need for sufficient within-site replication. A rain leaching experiment was also used to assess how precipitation affects loss of Cd in cellular compartments of O. lyellii tissues. Moss samples were subjected to an artificial rain solution of 0.01 M CaCl2 for 15, 30, 60, and 120 minutes using a gravity-fed rain device. A sequential elution procedure of dilute NiCl2 and HNO3 was used to quantify the metal concentrations in the inter-, extra-, and intra-cellular compartments of moss tissues. Preliminary results indicate that rain has some effect; more experiments are needed to elucidate the trends. Airborne metal concentrations will also be measured over multiple seasons at an urban site in Portland, OR using 24-hour PM10 filter samples collected via a high-volume air sampler alongside real-time meteorological and black carbon aerosol measurements. These data will be interpreted by positive matrix factorization source apportionment and compared to tissue concentrations from moss collected nearby.

Evaluating moss as biomonitors of atmospheric heavy metals in Oregon

255th National Meeting (2018)

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