Biomonitoring of atmospheric mercury levels with the epiphytic fern Lepisorus thunbergianus (Polypodiaceae).

The suitability of the epiphytic fern Lepisorus thunbergianus (Kaulf.) Ching, common in East and Southeast Asia, for the in situ biomonitoring of atmospheric mercury levels was investigated. L. thunbergianus is an evergreen fern with young, mature and old fronds throughout the year. Fertile mature fronds were used for the monitoring since the young fronds showed a high relative standard deviation (RSD) due to a shorter period of exposure, and the old fronds showed significantly high mercury concentrations with a slightly high RSD. When the mercury concentration in the fronds was plotted against the average mercury concentration in air, a significantly higher correlation was observed for the average value for the last 5-8 months. The regression equation y=13.6 x -1.4 was obtained, where "y" is the mercury concentration in the fronds (ng g(-1) dry mass (DM)) and "x" is the corresponding average concentration in ambient air (ng m(-3)). Atmospheric mercury levels can be estimated from the biomonitoring data: from the 95% confidence intervals, an atmospheric mercury concentration of 5 ng m(-3), estimated from a concentration of 70 ng g(-1) DM in fronds, corresponds to atmospheric mercury levels of between 3 and 8 ng m(-3).