The Influence of Air Pollution on the Concentration of Airborne Elements and on the Production of Stress-Ethylene in the Lichen Usnea hirta (L.) Weber em. Mot. Transplanted in Urban Sites in Oulu, N. Finland

Abstract

The purpose of the present study was to examine theresponse, as indicated by the production of stress-ethylene, of the lichenUsnea hirta, to a buffered acidic solution and to a solutioncontaining bisulfite ion, both at pH 4.0. In addition, the study investigatedthe accumulation capacity of U. hirta transplanted either to thevicinity of two streets with slow traffic, or to the vicinity of a highway inthe city of Oulu, N. Finland for a short period (45 d), and to analyze thecomparative production of stress-ethylene and the amounts of airborneelements accumulated in the thallus. Thalli of U. hirta manifested ahigh accumulation capacity for K, Ca, Na, Mg, Fe, Zn, and Mn in samplesexposed in one of the two streets with slow traffic in Oulu, in comparisonwith thalli left at the control site in the forest outside of the city. Twoof the observed elements, Pb and Ca, exhibited a positive correlation withthe concentration of ethylene detected consecutive to the treatment of lichenthalli with H2O (pH 6.8). The concentrations of stress-ethylene inlichen thalli retrieved from the streets with slow traffic and less cars(14,000 per day), soaked in solutions of NaHSO3 (pH 4.0), werehigher than those produced by thalli retrieved from a site near the highway(with 25,000 cars per day) and by thalli left in the forest. It is suggestedthat the streets with slow traffic and less cars are more polluted than thehighway as a result of bad ventilation conditions and a slow rate ofdispersion of airborne pollutants.