Article pubs.acs.org/est
Estimating Atmospheric Mercury Concentrations with Lichens Andrea Vannini,† Valentina Nicolardi,† Roberto Bargagli,† and Stefano Loppi*,‡ †
Department of Physics, Earth and Environmental Sciences and ‡Department of Life Sciences, University of Siena, 53100 Siena, Italy S Supporting Information *
ABSTRACT: The uptake kinetics of elemental gaseous Hg (Hg0) in three species of epiphytic lichens (Pseudevernia f urf uracea, Evernia prunastri, and Xanthoria parietina) were investigated under four different Hg concentrations (10, 15, 30, and 45 μg/m3) and three different temperatures (10, 20, and 30 °C) with the aim of evaluating the lichen efficiency for Hg0 accumulation and their potential use in the estimate of atmospheric concentrations of this metal in the field. The results showed that under our experimental conditions the lichens accumulated Hg according to exposure time and that the metal is not released back to the atmosphere after Hg0 was removed from the air (clearance). Pseudevernia f urf uracea showed the highest Hg accumulation capacity and Evernia prunastri showed the lowest, but in these species the metal uptake kinetics was affected by temperature. Xanthoria parietina showed an intermediate metal accumulation capacity and a Hg accumulation rate independent of temperature (in the range 10−30 °C). The use of first-order kinetics equations for Hg uptake in X. parietina and available field data on Hg bioaccumulation in this species allowed reliable estimates of atmospheric Hg concentrations in the environment.
1. INTRODUCTION
can allow an estimate of atmospheric Hg concentrations in the field.
Atmospheric mercury (Hg) pollution is a major concern worldwide.1 During the industrial period, Hg emissions to the atmosphere have greatly increased due to anthropogenic sources, and global atmospheric Hg deposition has tripled compared with preindustrial times.2 The primary anthropogenic sources of Hg are fossil fuel combustion, gold mining, metal and cement production, solid waste incineration, and chlor-alkali plants, with China being responsible for over 28% of current global Hg emissions.3 Mercury is included in the list of the top ten chemicals of major public health concern,4 and programs aiming at monitoring atmospheric Hg are promoted worldwide.5−7 Lichens, missing cuticle and stomata unlike leaves of higher plant, are efficient accumulators of Hg8 and are thus useful for monitoring its environmental distribution,9 especially in terrestrial ecosystems of remote regions.10 Although the scientific literature on the use of lichens in environmental biomonitoring of Hg0 is notable,11−14 the data obtained are qualitative rather than quantitative, i.e. they can be used to identify areas with different (spatial or temporal) Hg contamination, but do not allow estimation of average concentrations of atmospheric Hg in the study area. In this study, three different lichen species with a different ecology were exposed to four different Hg atmospheric concentrations under three different temperatures with the aims of (1) assessing the uptake kinetics of Hg0 and the reliability of each species as biomonitor and (2) evaluating if data from exposure experiments under controlled conditions © 2014 American Chemical Society
2. MATERIALS AND METHODS 2.1. Lichen Species. The three lichens species tested were Pseudevernia furf uracea (L.) Zopf, Evernia prunastri (L.) Ach., and Xanthoria parietina (L.) Th. Fr. These epiphytic (treeinhabiting) species were selected as they are commonly used in biomonitoring studies.15 They have a markedly different ecology: P. f urf uracea is a xerophytic (adapted to living in dry environments) to mesophytic (adapted to living in an environment having a moderate amount of moisture) species, and E. prunastri is a hygrophytic (adapted to living in moist environments) to mesophytic one, and both live in nutrientpoor habitats or in habitats with just a low level of eutrophication; X. parietina is a mesophytic to xerophytic species and is well distributed in habitats with a high level of eutrophication.16 Lichens were collected from remote and Hg-uncontaminated areas by harvesting the branch to which they were attached. After collection, lichens were transferred to the laboratory in paper bags and placed for 24 h in a climatic-chamber at 15 ± 2 °C, RH 55 ± 5%, and photoperiod of 12 h at 40 μmol m−2 s−1 photons PAR. Received: Revised: Accepted: Published: 8754
February 19, 2014 May 27, 2014 June 27, 2014 June 27, 2014 dx.doi.org/10.1021/es500866k | Environ. Sci. Technol. 2014, 48, 8754−8759
Environmental Science & Technology
Article
Figure 1. Mercury uptake kinetics in the lichens Pseudevernia f urf uracea (triangle), Xanthoria parietina (square), and Evernia prunastri (circle) at the temperature of 20 °C and at the atmospheric concentrations of 10 (top left), 20 (top right), 30 (bottom left), and 45 (bottom right) μg/m3 Hg. White symbols indicate the clearance. CV of the three replicates is always
