Air Quality Part 6 doc

118 Air Quality significant quantities in soils, are usually not detectable in air, thus, if found on leaves, they are mainly resuspended from soils (Vandenhove et al., 2009) The soil-to-plant transfer factor above 1.0 is reported for 40K, while values for uranium and thorium are much lower (10-4) (Uchida et al., 2007) In higher plants, the distribution of the radionuclides is uneven In tropical forest plants, for example, the highest 40K concentrations are found in stem, and the lowest in root, while 137Cs is mostly accumulated in root (Somashekarappa et al., 1996) Beryllium-7 (half-life 53.28 days) is produced by cosmic rays in spallation processes with light elements (nitrogen, oxygen, carbon) in the upper troposphere and lower stratosphere Its production depends on the Earth’s magnetic field, and the variations in its annual mean concentrations are a good indicator of changes in the atmospheric production rate caused by cosmic ray intensity The 7Be seasonal patterns are correlated to the stratosphere–to–troposphere exchange processes The 7Be concentration in ground level air in the midlatitudes has the maximum during spring and summer (e.g., Ajtić et al., 2008), caused by a seasonal thinning of the tropopause which allows the 7Be rich stratospheric masses to enter the troposphere (Gerasopoulos et al., 2003) Lead-210 (half-life 22.3 years) is an effective tracer of continental surface air masses history and often used to identify soil aerosols sources It mostly originates from the decay of uranium-238 in the Earth’s crust, but anthropogenic sources (uranium ores sintering, coal combustion, production or use of phosphate fertilizers) also contribute to the total 210Pb in air (UNCEAR, 1988) Deposition of 210Pb varies with season and geographical position The 210Pb concentration maxima in fall could be attributed to an enriched emanation of radon Radon emanation, and therefore concentration of 210Pb in air, is affected by atmospheric pressure, temperature inversions, covering vegetation, snow and ice ground coverage, etc Furthermore, important factors influencing the 210Pb concentrations in air are soil geology, continental and areas masses distribution, conditions of surface air layers, etc (Delfanti et al., 1999) Due to its half-life of 30 years, 137Cs is a good indicator of nuclear weapon atmospheric tests and nuclear power plant accidents on global scale Since 1986, 137Cs in ground level air has mainly originated from the Chernobyl nuclear accident, with concentrations of the order of µBq/m3, and with one or two maxima in summer and winter The 137Cs winter maxima are attributed to the inversion weather conditions and to soil dust air resuspension from the Chernobyl fallout (Todorovic et al., 1999) 1.2 Moss and tree leaves as biomonitors For several decades, air quality biomonitoring has been widely applied to detect and monitor the effects of trace elements pollution (Bargagli, 1998; Markert et al., 2003) Mosses and lichens are recognised as the most appropriate biomonitors of atmospheric trace elements and radionuclides contamination Many studies have demonstrated the ability of moss to absorb and accumulate trace elements in their tissue Due to the absence of root and cuticle, mosses uptake their nutritive elements from wet and dry atmospheric deposition (Rühling & Tyler, 1968) Mosses have also been recognised as valuable biomonitors in the assessment of temporal trends in trace metal accumulation (Harmens et al., 2008), and in spatial variations across national boundaries (Schröder et al., 2008) Mosses are also highly efficient in accumulating radionuclides and have been widely used as reliable bioindicators of radioactive contamination of the environment since the late 1960’s (Sumering, 1984; Steinnes, 2008; Frontaseyeva et al., 2009; Aničić et al., 2007; Barandovski et al., 2008; Guillén et al., 2009) Due to their continuous accumulation of elements, mosses offer Trace elements and radionuclides in urban air monitored by moss and tree leaves 119 information about the sources of pollution long after the pollution episode itself took place (Golubev et al., 2005) Being globally spread, mosses are an important tool in mapping global distribution of radionuclides following nuclear weapon atmospheric tests and in radioactivity monitoring in the vicinity of nuclear and coal power plants (Delfanti et al., 1999; Uğur et al., 2003) In 1986, mosses and lichens proved to be reliable indicators of environmental contamination after the nuclear plant accident in Chernobyl (Papastefanou et al., 1989; Hofmann et al., 1993) In the late 1990’s, mosses and lichen were used to estimate the level of contamination caused by the military use of depleted uranium (DU) in the Balkans (UNEP, 2002; Loppi et al., 2003; Frontasyeva et al., 2004; Popovic et al., 2008a) Since naturally growing mosses are often rare or absent in urban areas, the “moss bags technique’’ (active biomonitoring) has been developed in order to spatially and/or temporally assess deposition of trace elements in highly polluted areas (Goodman & Roberts, 1971; Vasconcelos & Tavares, 1998; Fernandez et al., 2004; Culicov & Yurukova, 2006) The technique offers several advantages compared to naturally growing mosses: one can precisely limit the time of exposure, acquire data on the concentrations of different elements in the sample prior to the exposure, and choose a most suitable site for moss transplantation The Sphagnum moss species are especially recommended for active biomonitoring for their large surface area and a number of protonated anionic functional groups (ion exchange sites) in the form of uronic acids However, moss bags tend to dry out and thus their efficiency in retaining elements varies with the environmental conditions, especially humidity (Al-Radady et al., 1993) Until now, only a few quantitative comparisons of biomonitoring methods with the standard measurements of atmospheric deposition have been published (Berg & Steinnes, 1997; Thöni et al., 1996; Aničić et al., 2009a,b) Moreover, the exact relationship between the element content in moss and the actual atmospheric deposition is not yet well understood, though some studies have given evidence of possible quantitative conversion with unsedimentable dry deposited particles ( Cu (9) > Pb (8) > As (5) > Al (4) > Fe (3) > Ni (3) ≈ Zn (2.5) > Mn (0.9) > Cd (0.5) In WET MB, the order for the most accumulated elements was somewhat different: Cu (68) > V (26) > Cr (21) > Pb (13) > Al (6.5) > As (6) > Fe (5) > Zn (4.5) > Ni (4) > Cd (1) > Mn (0.2) (Aničić et al., 2009b) The accumulation of Cu in WET MB was about eight times higher than for DRY MB Likewise, the content of Cr was about twice as high in WET MB Other elements, such as Pb, Al, Fe, and Zn, were slightly more accumulated in WET MB than in DRY MB In some moss bags, both dry and wet, a loss of Mn, compared to the initial material, was evident (10% and 80%, respectively) The loss of Mn caused by washing out and leaching from moss, was described in Couto et al (2004) The RAF values, obtained in this study, are significantly higher than the literature data (Adamo et al., 2003; Culicov & Yurukova, 2006) This is most likely related to higher atmospheric pollution in Belgrade urban area, and to lower initial concentration of the elements in used S girgensohnii moss S g S girgensohnii (DRY MB) S girgensohnii (WET MB) Element Initial Min Min Al 254 659 1960 1363 802 3523 1870 V 0.54 2.9 112 13 2.9 69 14 Cr 0.25 2.0 6.8 3.1 3.7 8.3 5.8 Mn 113 92 322 215 77 212 134 Fe 297 732 2496 1219 1026 4810 1682 Max Median Max Median Ni 2.4 1.9 41 8.7 4.5 30 12 Cu 2.1 10 49 20 42 476 144 Zn 20 44 105 71 85 264 113 As 0.11 0.38 2.2 0.67 0.53 5.4 0.80 Cd 0.18 0.19 0.36 0.27 0.25 0.50 0.36 Pb 2.2 7.0 38 20 14 63 31 Table Trace elements (μg g-1 of dry weight) in DRY and WET MB of S girgensohnii exposed in Belgrade urban area Trace elements and radionuclides in urban air monitored by moss and tree leaves 125 3.1.1 Trace elements accumulation in moss bags vs bulk deposition To compare the element accumulation in moss bags with the bulk deposition data, the moss element concentrations (μg g-1) were expressed as the deposition fluxes (μg m-2 day-1) and the Spearman rank correlation coefficients (r) were calculated to estimate a relationship between the element deposition flux in DRY MB/WET MB and BD The correlation between the element BD and the element deposition flux in WET MB was high for V (r=0.87), As (r=0.74), Fe (r=0.73), Al (r=0.71), and Ni (r=0.68) No correlation was found for Cd, Mn, and Zn The DRY MB vs BD highest correlation was found for Cu (r=0.85) Lower, but still significant correlation (r > 0.50), was obtained for Pb, Cr, and Zn (Aničić et al., 2009a) In general, trace elements may be deposited onto the moss surface either as dry particulates or dissolved and/or suspended in precipitation The elements may be retained by particulate entrapment, physicochemical processes such as ion exchange or by passive and active intracellular uptake (Tyler, 1990) Therefore, moss is not a mere passive filter Poor correlation for some element deposition fluxes in moss samples and BD probably indicates more complex mechanisms of element accumulation in moss Furthermore, due to splash effect and irregular surfaces, it is difficult to estimate the exact atmospheric deposition fluxes in moss bags Nevertheless, the concentrations of some elements (e.g., V, Fe, Co, As, Mo, Cd, Sb, and Pb) were found to be significantly correlated in moss and wet deposition (Couto et al., 1994; Berg & Steinnes, 1997) The rate of element uptake by moss increased markedly, but not regularly, with atmospheric humidity and precipitation, whereas their atmospheric level decreased (wet deposition), preventing the possibility of establishing a conversion factor for wet weather conditions (Vasconcelos & Tavares, 1998) Studies on the capture of atmospheric particles by moss have demonstrated that standardised active biomonitoring with moss bags provides a better capture efficiency of particles over 20 μm in diameter (sedimentable particles) less influenced by abiotic conditions like wind speed Therefore, it was suggested that particles trapped by bryophytes may be a major source of poorly water-soluble elements, and that moss content can reflect recent environmental conditions for dry and coarse depositions, especially for active biomonitoring experiments in highly polluted areas (Amblard-Gross et al., 2002) 3.1.2 Seasonal variations of trace elements in moss Trace elements content in moss bags was also analysed for the summer (May – October) and winter (November – April) seasons Seasonal variations in both DRY and WET MB samples were observed for all of the elements except Pb, Al, and Mn At all three sites, the highest variations were noticed for V and Ni, whose content was two and three times higher in winter than in summer, respectively (Fig 2) The content of As and Fe in moss bags were 1.5 times higher in winter than in summer This was not unexpected as these elements are markers for oil and coal combustion However, concentrations of Cu were increased in summer, especially in WET MB Moreover, the concentrations of Zn and Cd in WET and DRY MB were slightly higher in summer than in winter period These elements are markers for traffic sources, but our results point to some other local sources, more expressed during the warm period (Aničić et al., 2009a) Seasonal variations were also found for the elements in the bulk deposition, being higher in winter season (except for Pb, which was increased during summer time) In winter, much higher contents of V, Ni, As, and Fe were found in the bulk deposits 126 Air Quality 3.2 Radionuclides in moss bags Fission product 137Cs and naturally occurring 40K and 210Pb were detected in all of the eight subsamples of moss bags, while 7Be was detected only in one, with the activity of 60 Bq/kg V 400 400 DRY MB 350 WET MB BD 350 250 200 150 150 100 100 50 0 VF RB ec nM ar A pr -J un e Ju ly -S ep Ja p ct -D ySe O Ju l Ja ec nM ar A pr -J un e Ju ly -S ep p ct -D ySe O Ju l ec nM ar A pr -J un e Ju ly -S ep Ja ct -D O Ju l ySe p -2 -2 -1 200 Bulk deposition [μg m day] 300 250 50 HI Ni 140 DRY MB WET MB 140 BD 120 100 100 80 80 60 60 40 40 20 20 0 Ju ly -S ep O ctD ec Ja nM ar A pr -Ju ne Ju ly -S ep -2 VF Ju ly -S ep O ctD ec Ja nM ar A pr -Ju ne Ju ly -S ep Ju ly -S ep O ctD ec Ja nM ar A pr -Ju ne Ju ly -S ep -2 -1 Moss bags [ μg m day ] -1 120 Bulk deposition [ μg m day ] Moss bags [ μg m day ] 300 RB HI m-2 day-1) Fig Seasonal variation of V and Ni daily fluxes (mg for DRY MB and WET MB, and BD for 3-month periods in 2005/2006 at the study sites (VF, RB, and HI) The absence of 7Be in the subsamples could be explained by its decay, since the period between the sample arrival in the laboratory and the analysis was nearly 60 days Taking into account the standard uncertainty of the method and the volume of the composite sample, the distribution of the activities of the detected radionuclides in the eight subsamples was rather uniform with the differences not exceeding 30% (Popović et al., 2009b) The level of the annual activities of the radionuclides implied that the exposure time could be reduced to a month, and that would enable monitoring seasonal variations in the content of radionuclides in air The mean activities with standard deviations of 40K, 210Pb, and 137Cs in moss bags (S girgensohnii), Trace elements and radionuclides in urban air monitored by moss and tree leaves 127 are given in Table For comparison, the content of these radionuclides in naturally growing mosses (Hypnum cupressiforme) in Southern Serbia (Borovac) are also presented in the table Location Belgrade Activity (Bq/kg) 40K 210Pb 245 ± 34 315 ± 25 137Cs 28 ± 7Be / Borovac 298 ± 42 210 ± 52 226 ± 22 228 ± 34 Table Activities of the radionuclides in moss bags (S girgensohnii) exposed in Belgrade (Popović et al., 2009b) and in H cupressiforme, Borovac (Popovic et al., 2008b) The activity ratio 210Pb/40K of 1.30 was calculated The ratio could provide a sound basis for the 210Pb activity estimation by solely measuring the activity of 40K, which is more easily detected, and with a lesser uncertainty than 210Pb (Popović et al., 2009b) The mean activities of the detected radionuclides in moss bags were in the range of the values reported for the local moss (H cupressiforme) in the region (Krmar et al., 2007; Popovic et al., 2008b), with differences arising from the species, the method, local climate and soil characteristics Krmar et al (2007) found measurable, even significant concentrations of 7Be in H cupressiforme, with an increase in summer and autumn (up to 920 Bq/kg), but the sampling in the study took place over a 14–month period Beryllium-7 was also found in naturally growing moss (H cupressiforme) in the rural area of Southern Serbia (Popovic et al., 2008b) (Table 2) As can be seen from Table 2, there are no significant differences in the content of 40K in naturally growing mosses in Southern Serbia and in the urban area of Belgrade On the other hand, higher concentrations of 210Pb in Belgrade indicate a contribution of anthropogenic air pollution sources Significantly higher activities of 137Cs, as well as the detectable amount of 7Be, in mosses sampled in Southern Serbia are due to a longer, undefined exposure period (in the Belgrade study, the exposure period of one year was precisely defined) Hence, the observed differences mirror the differences in the accumulation period Before the Chernobyl nuclear plant accident in 1986, the concentrations of 137Cs in moss and lichen in Serbia were under Bq/kg (Djuric & Popovic, 1994) Immediately after the accident and later, the contents of 137Cs in mosses and lichens, sampled in a mountainous region, was in the range of 8–18 kBq per kg of dry weight (Djuric et al., 1992, 1996; Popović et al., 1996) In 1997, the activities of 137Cs in the naturally growing mosses in a region in Serbia were up to kBq/kg, while the soil-to-moss transfer factors calculated for the same region in 2000 were in the range of 3.0–10.0 (Popović et al., 2009a) High transfer factors for 137Cs and 210Pb from soil to mosses were also found in Southern Serbia, in the range of 1–10 and 4–10, respectively (Popovic et al., 2008a) Still, as already mentioned, naturally growing mosses are unlikely to be found in urban areas, and the active moss monitoring is therefore a suitable alternative technique for monitoring contents of radionuclides in urban air Furthermore, this method solves some of the problems in monitoring using naturally growing mosses, such as intercalibration of different species of mosses and transformation of concentrations in moss to absolute deposition rate (Steinnes, 2008) Frontasyeva et al (2009) proposed a linear correlation between the concentrations of 137Cs in mosses Amoss and in air Aair: Aair (Bq/m3) = 3.3 x 10-8 (kg/m3) x Amoss (Bq/kg) (2) 128 Air Quality When applying this relationship to the activity of 137Cs in moss obtained in our study, the calculated 137Cs activity in air is 0.924x10-6 Bq/m3, which is under the lower limit of detection in our measurements (1x10-6 Bq/m3) To conclude, since the Belgrade study showed that the exposure time for the moss bags technique could be reduced to a month, the technique could be used to monitor the level of radionuclides’ contents in air, as well as to follow their seasonal variations 3.3 Trace elements in tree leaves Seasonal accumulation trends of elements’ concentration in leaves have been well known and reported for many plant species (Kim & Fergusson, 1994; Bargagli, 1998; Piczak et al., 2003) In Belgrade urban area, the elements’ concentration were determined in leaves of A hippocastanum and Tilia spp at the beginning (May) and the end (September) of the vegetation seasons over a period of 2002 – 2006 An increase of the element concentrations (p