Mercury content and elemental composition of fruticose lichens from Nahuel Huapi National park (Patagonia, Argentina): Time trends in transplanted and in situ grown thalli

Abstract

Lichens have a unique structure involving the symbiosis of fungus and algae and can grow on almost any type ofsubstrate. They absorb gases, water, nutrients and pollutants through their cortex, and thus are good indicators ofenvironmental processes, enabling the biomonitoring of environmental pollutants. These organisms are widelydistributed; however, as certain species do not occur in some areas, transplants are commonly used to monitor airpollution. In this study, transplants of the fruticose species Protousnea magellanica were set up at the EMMAStation (Global Mercury Observation System, GMOS) located at a suburban site of San Carlos de Bariloche citywithin Nahuel Huapi National Park (North Patagonia, Argentina). The transplants were used to assess the uptakeof certain elements, particularly the accumulation of mercury. Periodic samplings of the transplanted speciesP. magellanica and the naturally occurring Usnea pusilla were performed concurrently at the experimental siteover 483 days of experimental exposure. The elemental composition and concentration of the thalli of thesespecies were determined by Neutron Activation Analysis in a nuclear reactor. Atmospheric mercury concentration (Gaseous Elemental Mercury, GEM) was monitored at the EMMA Station by an automated cold vaporatomic fluorescence system (Tekran 2537B). Mercury concentrations in the lichens were at least three orders ofmagnitude higher than atmospheric mercury levels (0.80–0.94 ng/m3, ppt), highlighting the accumulation capacity of these organisms. Concentrations found in P. magellanica thalli (0.080–0.327 μg/g dry weight, ppm) laywithin the range of values reported previously in lichens from the Nahuel Huapi National Park with lowanthropogenic impact. During experimental exposure both lichen species displayed the same trend in Hg content.Total Hg increased from T0 to T1 (day 25) and then decreased up to approximately T4 (day 385). In U. pusilla, thepositive relationship between Hg content and lithophilic elements such as La, suggested preferential Hg uptakefrom airborne particles (deposited dust).