Deciduous tree leaves in trace elements biomonitoring: A contribution to methodology

Ecological Indicators 11 (2011) 1689–1695

Contents lists available at ScienceDirect

Ecological Indicators journal homepage: www.elsevier.com/locate/ecolind

Deciduous tree leaves in trace elements biomonitoring: A contribution to methodology ´ M. Tomaˇsevic´ a,∗ , M. Aniˇcic´ a , Lj. Jovanovic´ b , A. Peric-Gruji c´ c , M. Ristic´ c a

Institute of Physics, University of Belgrade, Pregrevica 118, 11000 Belgrade, Serbia Faculty of Ecological Agriculture, Educons University, V. Putnika bb., 21208 Sremska Kamenica, Serbia c Faculty of Technology and Metallurgy, University of Belgrade, Karnegijeva 4, 11120 Belgrade, Serbia b

a r t i c l e

i n f o

Article history: Received 29 January 2011 Received in revised form 11 April 2011 Accepted 13 April 2011 Keywords: Urban air pollution Trace elements Biomonitoring Deciduous trees Leaves ICP-MS

a b s t r a c t Air quality biomonitoring using plant leaves has been widely applied to assess the effects of atmospheric pollution. Although practiced for many years, it has not given completely satisfactory data, due to different and even opposing results. This study comprises an investigation on the content of some trace elements (Al, As, Ba, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Sr, Cd, Pb) in leaves of four tree species common for the urban area of Belgrade (Serbia). The assay took place in July 2009 when the selected trees (Acer platanoides, Aesculus hippocastanum, Betula pendula, Tilia cordata) were in the maximum of physiological activity during the vegetation season. Among the investigated species, leaves of A. platanoides contained the highest concentrations of the measured elements. The assumption that a large green area in the Belgrade city periphery would be a suitable control site appeared to be disputable due to the substantial load of the elements obtained in the leaves. It was shown that even a short rinse with bidistilled water (3–5 s), applied twice to the leaves prior to chemical analysis, led to a significant decrease of some element concentrations (most pronounced for Al, Fe and Pb in all species, but also evident for Cu, Cr, Co and Zn for some of them). However, by washing leaves, the representativeness of leaf samples per studied site could be improved due to removal of some superficial loosely adhered impurities and so diminished large variability of element concentrations among leaf subsamples providing more representative information on the element content in leaves per site, and the area, respectively. © 2011 Elsevier Ltd. All rights reserved.

1. Introduction In recent years, plant biomonitoring of contaminant deposition, notably trace elements, has been widely applied as a complementary to conventional methods (Markert, 1993; Bargagli, 1998; Weiss et al., 2003; Fujiwara et al., 2011). Plants provide information, not only on the quality/quantity of air pollutant concentrations, but also the effects of air pollution on living systems. Trees are very efficient at trapping atmospheric particles and have a special role in reducing a level of fine, “high risk” respirable particulates, which have potential adverse effects on the environment and human health (Beckett et al., 2000; WHO, 2003). Leaves of various tree species, both evergreen and deciduous, have been studied for this purpose in urban areas, including a search for sensitive tree species and approval of the validity of using such leaves as trace element biomonitors (Bargagli, 1998; Weiss et al., 2003). Evaluation of the validity of a biomonitor is a complex task and may require aspects such as multi-year temporal trend

∗ Corresponding author. Tel.: +381 11 3713004; fax: +381 11 3162190. ´ E-mail address: [email protected] (M. Tomaˇsevic). 1470-160X/$ – see front matter © 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.ecolind.2011.04.017

consistency in element accumulation by leaves (Aniˇcic´ et al., 2011). There has been much discrepancy in published reports on methodological points regarding representative sampling and sample preparation. Different approaches to the issue of leaf washing, i.e. whether or not leaves should be rinsed (and under what conditions) prior to trace element determinations may give different results (Markert, 1993; Bargagli, 1998; Luyssaert, 2002). Several factors may affect the “washability” of leaves, such as type of pollutant, deposition processes and depositing plant material (Markert, 1993; Bargagli, 1998), as well as the length of the applied washing procedure. There are diverse approaches to the length and manner of washing leaf samples. Although rinsing leaves with water is widely accepted, various chemicals (diluted acid solutions, detergents) are still in use (Azcue and Mudroch, 1994; Lin et al., 1995; Wyttenbach and Tobler, 1998). Thus, samples of Equisetum variegatum were soaked in different washing media (water, acid solution, detergents) for approximately 3 h, followed by ten repeated rinses with double distilled water (Azcue and Mudroch, 1994). In a study of metal contamination in and on Abies balsamea, chloroform was used, and then double rinsing with deionized water (Lin et al., 1995). Similarly, treatment with toluene/tetrahydrofuran

1690

M. Tomaˇsevi´c et al. / Ecological Indicators 11 (2011) 1689–1695

was applied during examination of surface element contamination on Picea abies (Wyttenbach and Tobler, 1998). A combined washing procedure using phosphate-free detergent with weak acid solution and rinsing with distilled water was used on leaves of Populus alba. Tap water and shaking for 30 min was applied to Quercus ilex leaves during assessment of the elemental composition of dry deposition (Alfani et al., 1996). Moreover, the results may refer to combined tap, distilled and deionized water respectively, as reported for leaves of Salix fragilis, Acer platanoides, Tilia platyphillos, and Betula verrucosa (Piczak et al., 2003). Certainly, if some chemicals or tap water are used for leaf washing, sample contamination is likely to occur. However, distilled or deionized water is used most often for washing leaves during sample preparation. Thus, to study airborne trace element pollution, after freezing at −30 ◦ C, leaves of Quercus robur and Pinus pinaster were washed with distilled water for 15 min with shaking (Aboal et al., 2004). Also, Q. ilex leaves were thrice washed in distilled water with shaking (15 min each) (De Nicola et al., 2008). Some authors report washing during sample preparation without a description of the procedure duration. Thus, deionized water was used for washing deciduous leaves in the development of a metal (Pb, Cd) accumulation index in Populus tomentosa, Sophora japonica and Catalpa speciosa (Liu et al., 2007). Also, to remove adhering particles Cedrus libani needles were rinsed three times with demineralised water (Onder and Dursun, 2006). Leaves of Nerium oleander were washed in running distilled water (Aksoy and Ozturk, 1997) and Pittosporum tobira with running ultra-pure water (Palmieri et al., 2005). Some authors decided to base their trace element studies on unwashed leaves, such as: P. abies, Fagus sylvatica (Mankovska et al., 2004); Betula pubescens; Robinia pseudo-acacia (C¸elik et al., 2005); seven deciduous species (Baycu et al., 2006) N. oleander, Pinus pinea; Q. ilex (Monaci et al., 2000). Since there are significant differences in element concentrations in unwashed and washed leaf samples, many questions arise about the approach such as the manner of the washing procedure, the duration and leaf “washability”. This study was undertaken as part of a larger project, conducted within several countries (Bulgaria, Greece, Romania, Russian Federation, Serbia and Turkey) in the Black Sea region (BSEC, 2010), aiming to select tree species appropriate for regional biomonitoring. The objective of the study was to clarify some methodological points (sampling – control of the experiment, sample preparation) to gain an insight into the representative information about the element content of the leaves of some common urban trees in the region.

hippocastanum L. (horse chestnut), Betula pendula Roth (European white birch), Tilia cordata Mill. (littleleaf linden), and A. platanoides L. (Norway maple).Tree leaves at about 2 m height were picked by individual wearing polyethylene gloves in the middle of July, 2009. For each species five trees of approximately the same age were selected per site. Five subsamples (10–30 fully developed leaves) were randomly chosen from all sides of the crown. The subsamples were packed in polyethylene bags and transported to the laboratory.Half of the leaves was briefly rinsed (for 3–5 s) with bidistilled water twice in polyethylene containers, while the other half of the samples was left unwashed. Both were than dried in an oven at 40 ◦ C for 48 h. Leaf material was pulverized using agate mortars, packed in polyethylene bags and kept in stable laboratory conditions prior to chemical analysis. Portions of approximately 0.4 g of leaves (dry weight) were placed in silicon vessels with 3 ml of 65% HNO3 (Suprapure, Merck) and 2 ml of 30% H2 O2 and then digested for 2 h in a microwave digester (speedwaveTM MWS-3+, BERGHOF). After digestion the samples were diluted with distilled water to a total volume of 25 ml. 2.3. Chemical analysis The element concentrations (Al, As, Ba, Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb, Sr, V and Zn) in leaves were measured by inductively coupled plasma mass spectrometry (ICP-MS) using an Agilent 7500ce spectrometer equipped with an Octopole Reaction System (ORS). Calibration was performed with external standards obtained by appropriate dilution of Fluka Multielement Standard Solution IV. Blank and calibration standards were prepared in 2% HNO3 for all the measurements except for those used to determine the detection limits. Tuning solution containing 1 ␮g l−1 Li, Mg, Co, Y, Ce and Tl (Agilent) was used for all instrument optimizations. The accuracy and precision of the analytical procedures were verified through analysis of the standard reference material, lichen-336 (IAEA). The recovery range was 90–95%. All results were calculated on a dry weight basis. 2.4. Data analysis Data handling included basic statistics for the element concentrations measured in washed and unwashed leaf samples of the selected tree species. The applied Shapiro–Wilk test showed nonnormal distribution of the results. Non-parametric statistics (Sign test and Kruskal–Wallis H test) was used to assess the significance of differencess (p = 0.05) of element concentrations between groups of leaves.

2. Experimental 2.1. Study area The study was conducted in Belgrade, the capital of Serbia, with a population of about 1.7 million inhabitants. There are many old buses and trucks on the streets, and leaded gasoline was still widely used during the investigation. Three representative urban sites in – dev – Park (KP), an area of heavy traffic: Student’s Park (SP), Karador Botanic Garden (BG), and a control site: Koˇsutnjak (K) (a recreation area cca. 10 km in the city periphery) were chosen for the investigation (Fig. 1). 2.2. Sampling and preparation of tree leaves for chemical analysis Sampling and analyses were performed according to the agreed project (BSEC) protocol, and with regard to the relevant points for leaf sampling and analysis (Bargagli, 1998; UNECE, 2007). Leaves were taken from deciduous trees common in this area: Aesculus

3. Results The element concentrations (␮g g−1 ) in unwashed and washed leaves from four common tree species growing in three heavy traffic sites and the control site in the urban area of Belgrade are presented in Table 1. The brief double rinsing with water (3–5 s) decreased of Al, Fe and Pb concentrations (p = 0.05) in leaf samples of all investigated species (Fig. 2). In addition, washed leaves of A. platanoides contained lower concentrations of Cu and Cr, and those of A. hippocastanum less Co and Zn (Table 1). The obtained element content in washed leaf samples taken from traffic-congested areas of Belgrade significantly varied among the species (Fig. 3). Thus: A. platanoides had markedly the highest Pb, Cr and Cd concentrations in comparison with leaves from the other trees; concentrations of Mn, Fe and Al were higher, as well; B. pendula accumulated Ba, Ni and Zn at least twice as efficiently as the other species; T. cordata accumulated more Cu and Sr than the other species.

M. Tomaˇsevi´c et al. / Ecological Indicators 11 (2011) 1689–1695

1691

Table 1 Mean element concentrations (␮g g−1 ) in unwashed and washed leaves of four tree species sampled in the middle of July, 2009 from three heavy traffic sites (SP, KP, BG) and the control site (K) in Belgrade. Element

A. platanoides SP Average

SD

Unwashed leaf samples Al 212 63 V 0.94 0.17 Cr 1.88 0.52 Mn 377 50 Fe 381 123 Co 0.14 0.07 Ni 1.62 0.34 Cu 14 5.00 Zn 16 4 As 0.52 0.07 Sr 39 10 Cd 0.06 0.02 Ba 16 3 Pb 6.04 1.31 Washed leaf samples Al 99 23 V 0.54 0.15 Cr 1.20 0.39 Mn 457 94 Fe 183 65 Co 0.14 0.06 Ni 1.47 0.43 Cu 7.07 1.69 Zn 14 2 As 0.60 0.39 Sr 45 6.9 Cd 0.05 0.02 Ba 13 1 Pb 3.55 0.47 Element

B. pendula KP Average

BG SD

Average

K SD

Average

SP SD

SD

Average

BG SD

Average

K SD

Average

SD

403 1.95 2.61 307 953 0.21 2.30 17 49 0.41 36 0.09 24 5.14

115 0.73 1.30 80 308 0.14 0.95 6.57 9 0.24 7 0.03 3 2.16

229 0.92 2.37 205 585 0.86 1.64 12 39 0.72 41 0.13 15 11

31 0.06 0.25 84 33 1.05 0.19 2 72 6 0.17 24 0.09 4 3.62

223 0.56 0.78 116 285 0.34 2.11 7.94 44 0.15 10 0.09 9 2.22

63 0.25 0.50 42 76 0.40 1.16 2.21 1 0.09 5 0.03 1 1.03

120 0.76 0.56 34 167 0.22 3.10 7.26 61 0.51 29 0.04 41 4.91

33 0.19 0.20 12 45 0.12 0.53 1.08 50 0.24 4 0.03 26 1.51

117 1.66 3.07 30 219 0.13 3.42 7.42 53 0.24 14 0.16 16 3.04

25 0.53 4.79 8 44 0.04 2.23 2.38 42 0.08 2 0.21 4 0.70

95 0.68 1.28 46 237 0.46 2.48 7.58 40 0.45 19 0.08 26 5.39

20 0.36 0.54 10 55 0.64 1.47 1.19 16 0.05 6 0.03 7 0.96

128 0.37 0.61 65 161 0.35 2.48 6.79 57 0.10 6 0.09 20 1.89

22 0.03 0.66 7 22 0.54 1.69 0.62 32 0.06 3 0.07 7 0.50

207 1.04 1.78 270 516 0.20 2.07 13.07 50 0.27 48 0.50 20 4.44

79 0.09 0.47 43 160 0.15 0.61 3.85 10 0.09 12 0.81 4 1.40

147 0.91 1.55 182 371 0.21 1.55 9.19 31 0.50 36 0.10 12 7.98

40 0.72 0.50 51 110 0.16 0.54 2.23 9 0.14 21 0.03 2 2.88

127 0.59 0.52 164 189 0.04 1.12 9.17 54 0.24 21 0.06 18 1.87

27 0.10 0.10 53 39 0.03 0.08 1.91 8 0.22 7.5 0.02 4 0.52

77 0.64 0.53 36 113 0.26 3.14 6.09 64 0.54 31 0.04 41 3.88

39 0.28 0.21 12 55 0.03 0.59 0.58 50 0.20 7 0.01 28 1.61

92 1.36 1.34 50 224 0.09 2.04 8.43 60 0.15 23 0.05 20 2.46

16 0.38 0.48 8 21 0.11 1.17 1.39 49 0.06 3 0.02 5 0.50

62 0.46 0.64 46 133 0.13 2.17 5.37 32 0.33 19 0.08 26 4.05

5 0.10 0.17 6 11 0.05 0.96 1.20 16 0.13 10 0.05 9 0.33

88 0.52 0.40 72 127 0.07 2.11 6.87 57 0.40 11 0.10 24 2.57

10 0.14 0.10 3 10 0.02 0.61 0.44 23 0.40 2 0.01 7 1.33

T. cordata

A. hippocastanum

SP Average

Average

KP

KP SD

Unwashed leaf samples Al 250 63 V 0.93 0.23 Cr 1.06 0.29 Mn 103 43 Fe 371 78 Co 0.06 0.04 Ni 1.60 0.33 Cu 64 41 Zn 19 2.89 As 0.63 0.15 Sr 54 11 Cd 0.02 0.01 Ba 11 4 Pb 5.62 1.03 Washed leaf samples Al 100 8 V 0.33 0.21 Cr 0.52 0.11 Mn 82 42 Fe 160 16 Co 0.00 0.00 Ni 1.29 0.22 Cu 21 13 Zn 15 3 As 0.62 0.34 Sr 56 20 Cd 0.01 0.00 Ba 11 2 Pb 4.22 1.08

Average

BG SD

Average

K SD

Average

SP SD

Average

KP SD

Average

BG SD

Average

K SD

Average

SD

323 3.09 2.40 84 567 1.46 3.35 11 22.63 0.37 45 0.07 13 3.85

130 1.38 0.76 49 195 2.34 0.95 3 5.50 0.13 17 0.02 3 0.89

235 0.73 1.17 43 535 0.01 1.20 13 32.46 0.33 89 0.02 20 6.06

35 232 0.11 0.42 0.33 0.35 10 9 105 292 0.02 0.49 0.22 1.22 1 9 6.10 25.03 0.05 0.09 11 1 0.01 0.05 3 3 1.47 1.34

20 182 0.06 0.68 0.02 0.93 6 71 12 325 0.84 0.00 0.21 0.87 1 18 2.86 17 0.03 0.71 1 8 0.01 0.01 1 4 0.27 5.51

41 0.13 0.17 56 92 0.00 0.08 8 5 0.61 2 0.00 2 1.17

251 1.90 1.95 117 530 0.19 2.16 11 24 0.37 38 0.04 12 3.88

113 152 1.30 0.88 0.88 1.55 37 49 236 385 0.11 0.09 0.80 1.88 2 11 7 19 0.15 0.84 4 36 0.01 0.04 1 11 1.29 5.93

28 194 0.23 0.41 0.28 0.31 26 94 82 302 0.07 0.19 0.51 0.96 2 9 4 22 0.38 0.06 11 -2 0.05 0.05 4 4 1.57 1.20

45 0.10 0.14 17 43 0.33 0.12 2 3 0.02 1 0.01 1 0.28

134 1.11 1.39 80 288 0.07 1.87 9.93 24 0.17 54 0.07 12 2.40

34 0.53 0.42 51 53 0.08 1.05 2.06 8 0.05 15 0.02 2 0.65

149 1.47 0.92 47 304 0.00 1.19 10.68 25 0.30 107 0.02 22 4.25

22 161 1.85 0.63 0.12 0.61 4 20 30 232 0.00 0.00 0.14 1.51 0.80 9.20 3 20 0.06 0.13 13 6 0.00 0.04 4 6 0.70 1.56

41 114 0.04 0.56 0.11 1.09 7 78 48 208 0.00 0.04 0.23 1.49 0.89 21 0 15 0.01 1.03 0 14 0.00 0.01 2 4 0.21 3.75

24 0.18 0.29 42 67 0.02 0.29 18 4 0.58 6 0.00 2 0.70

125 0.73 1.19 116 297 0.02 1.25 8.85 18 0.16 45 0.03 12 2.49

29 91 0.32 0.32 0.58 0.56 40 55 57 240 0.02 0.00 0.50 0.74 1.24 9.06 5 16 0.03 0.32 9 39 0.00 0.01 0 7 0.69 3.77

11 125 0.05 0.60 0.12 0.55 26 131 33 257 0.00 0.00 0.28 1.14 1.70 9.92 5 18 0.23 0.10 6 0 0.00 0.05 4 5 0.69 1.68

37 0.13 0.10 6 44 0.00 0.16 3.14 6 0.01 1 0.01 1 0.46

1692

M. Tomaˇsevi´c et al. / Ecological Indicators 11 (2011) 1689–1695

– dev – Park (KP), Botanic Garden (BG) and the control site – Koˇsutnjak (K). Fig. 1. Map of the sampling sites in the Belgrade urban area: Student’s Park (SP), Karador

4. Discussion

Fig. 2. Diminished element content in leaves after a short-rinsing procedure (3–5 s, twice).

Although the control site (K) is situated in a large green area of the Belgrade city periphery, and was presumed to be a background place, our results showed that there was substantial leaf loading with the elements in comparison to the other urban sites (Table 1), except for significantly lower amounts of Pb, As and V (Fig. 4). In the deciduous tree leaves from traffic-congested areas of Belgrade, the anthropogenic influence was evident from the presence of most elements at concentrations significantly above the baseline level – “Reference Plant” (RP) values (Markert, 1992), especially for Pb, As and V (Fig. 4).

Although leaves of deciduous trees are recognized as useful air pollution biomonitors for trace elements (Markert, 1993; Bargagli, 1998), many difficulties arise when comparing data among studies, not only due to the use of various plant species, but also from the application of different experimental approaches. Published descriptions of leaf sample preparation prior to chemical analysis most frequently lack details about the washing procedure, including its duration. Diverse washing procedures may substantially affect the leaf element content. Even the short aqueous rinsing procedure (3–5 s, twice) applied in this study resulted in significant concentration decreases of Al, Fe and Pb in washed leaf samples from all investigated tree species, as well as Cu and Cr in A. platanoides and Co and Zn in A. hippocastanum leaves. While Al and Fe are considered as predominantly of crustal origin, and likely to be constituents of resuspended soil particles (in urban areas may also come from traffic and other sources), the other above-mentioned elements are considered as mostly of anthropogenic origin (Nriagy and Pacyna, 1988). It may be assumed that these elements (especially Al and Fe) were probably deposited on leaves either as constituents of coarse particles, loosely adhered to the leaf surface, or in small, watersoluble particles (Baker and Jickells, 2006). As suggested recently (Birmili et al., 2006), water solubility of elements depends more on the element than on the particle size. Thus, it is assumed that Al and Fe are of low solubility, while Pb is among medium water soluble elements.

M. Tomaˇsevi´c et al. / Ecological Indicators 11 (2011) 1689–1695 30

350

1693

2.5 A. platanoides

300

B. pendula

25

2

Concentration [μg g-1]

T. cordata 250

A. hippocastanum

20 1.5

200 15 150

1 10

100 0.5

5

50

0

0 Fe

Al

Mn

Sr

0

Zn

Ba

Cu

Pb

Ni

Cr

V

As

Co

Cd

Fig. 3. Concentration (␮g g−1 ) of trace elements in washed leaves from four deciduous tree species, common for the Belgrade urban area and sampled in mid July, 2009.

6

4 BG

Concentration [μg g-1]

5 3

K

4 3

RP

2

2 1 1 0

Pb

V

As

0

Pb

V

Concentration [μg g-1]

A. platanoides 4

4

3

3

2

2

1

1

0 Pb

V

T. cordata

As

B. pendula

As

0

Pb

V

As

A. hippocastanum

Fig. 4. Concentrations (␮g g−1 ) of Pb, V and As in washed leaves of four tree species sampled in the Belgrade urban area (BG) in comparison with the control site (K) and the “Reference Plant” (RP) values.

Certainly, by longer leaf washing, a number of elements may be removed from the surface, and some of them may presumably leak from the leaf internal content. Also, washing samples in different ways may contribute to greater element removal from the leaf surface. In our previous study of the Belgrade urban area, washing A. hippocastanum and Corylus colurna leaves with bidistilled water in an ultrasonic bath for 30 min led to detection of Pb, Cu and Zn in

the rinsed off fraction (Tomaˇsevic´ et al., 2005). Also, thrice washing Q. ilex leaves in distilled water with shaking for 15 min removed Cr, Cu, Fe, Pb, V and Zn (De Nicola et al., 2008). Washing leaves of N. oleander in running distilled water may remove elements such as Cd, Zn, and Cu (Aksoy and Ozturk, 1997). In leaves of P. tobira, the Pb content was also significantly lower after washing with running ultra-pure water (Palmieri et al., 2005). It appears that the washing procedure prior to chemical analysis is a critical point in biomonitoring studies, since removal of particles from a leaf surface strongly depends on the washing treatment and its duration. In a recent study on both washed and unwashed leaves of Q. ilex, it was reported that the unwashed leaves more clearly spotlight differences in air contamination between urban and remote areas and among urban sites (De Nicola et al., 2008). However, the results obtained in our study for deciduous trees from the Belgrade urban area, showed that standard deviations for element concentrations were higher for the unwashed than for washed leaf samples at each studied site. The short rinsing of leaf samples prior to chemical analysis may have removed accidental impurities, i.e. large loosely adhered particles, which anyhow may be easily lost from the leaf surface by either wind or rain. Accordingly, the short washing procedure would diminish the large variability of element concentration between leaf subsamples taken per tree or studied site, and thus provide more reliable information about the representative element content in leaves at each site and the area, respectively. Further discussion of our results is related to the data obtained for the washed leaf samples only. Selection of a control site for studies carried out in urban areas is also questionable due to difficulties in defining the parameters of what a control is. The control of an experiment should be some reference point reflecting the starting level of the investigated change/phenomenon. In the case of trace element biomonitoring using deciduous tree leaves, attention should be paid to the phenotype of the control plant growing at the chosen background site. If that site is too far from the polluted experimental area, the effect of different environmental conditions on the plant genotype should also be considered. However, due to transport of air pollutants, even large green areas in the city periphery can hardly be assumed as reliable control sites, as shown here. Therefore another “reference point” for trace element loading in leaves sampled from an urban area could be the System of the “Reference Plant” (RP) values as the element baseline level assessed for plants (Markert, 1992). However, this RP system is an approximation and does not involve

1694

M. Tomaˇsevi´c et al. / Ecological Indicators 11 (2011) 1689–1695

many specific factors (species, age, location, etc.). Thus, the element content of young, fully developed leaves at the beginning of the vegetation season seems to be a more appropriate control for any later increase of element content in mature leaves, as shown previously (Aniˇcic´ et al., 2011). Such a control point is especially valid for nonessential elements monitored as air pollutants (Pb, Cd, As, etc.), but is not accurate for some other, essential elements (Cu, Zn, V, etc.), which could be translocated from senescent leaves to nonsenescent plant tissue and stored for future growth of young leaves. As suggested in numerous studies, the trace element content in leaves is also influenced by species specific characteristics. Our results indicated substantial loading of some elements, like Pb and As, as well as V, Ni, Al, Cu, Fe and Al, in the leaves. It is been widely accepted that most of these elements are emitted from anthropogenic sources and in urban areas with a major traffic influence. In general, element content in tree leaves may originate from the soil by uptake via roots and/or by atmospheric deposition of particles on vegetation and thus foliar uptake. In higher plant biomonitoring, the contribution of these two pathways in the total leaf element content is not easily distinguished. Although soil in the central area of Belgrade contains high concentrations of potentially toxic metals it is likely that the present alkaline conditions (pH > 8.0) (Tomaˇsevic´ et al., 2004; Marjanovic´ et al., 2009) cause lower element solubility and lower availability for plants. Thus, in such environmental conditions, an atmospheric origin of the elements in leaves of the investigated species may be assumed. In this study, the highest concentrations of most elements determined were obtained for leaves from A. platanoides. However, this does not mean that this species is also the best biomonitor. This finding should be checked further for consistency in element leaf loading at such a level through a multi-year investigation. For example, among the other species in this study, leaves of A. hippocastanum had no prominent amount of any measured element, but this species showed a consistent response to the air trace element content through an earlier multi-year study in the Belgrade ˇ cur ´ et al., 2010; Aniˇcic´ et al., 2011). urban area (Su Evaluation of the validity of a biomonitor appears to be a complex task, and may require other aspects, apart from leaf element concentration level, such as temporal trend consistency in a multiyear investigation. The most important data for comparison among biomonitoring studies would be representative information referring to the same methodological procedure (sampling and sample preparation). Also, it would be of crucial importance to use standardized methodology as much as possible, and at least to specify the methodological procedures in publications in more detail.

5. Conclusion In the Belgrade urban area, A. platanoides leaves contained higher trace element concentrations than the other investigated tree species (A. hippocastanum, B. pendula, and T. cordata). The assumption that a large green area in the city periphery is a suitable control site appeared to be disputable due to the substantial load of the trace elements found in the leaves. Element content measured in leaves strongly depends on sample preparation, and even brief rinsing with bidistilled water (3–5 s, twice) caused a significant decrease of element concentrations (Al, Fe, Pb, etc.) in the samples. On the other hand, by washing leaves, the representativeness of leaf samples per studied site is improved due to removal of some superficial loosely adhered impurities. Leaf element contents obtained for the same tree species taken from different urban areas are not comparable without applying standardized sampling and sample preparation procedures as much as possible. Focus on some methodological steps is necessary and may be crucial for

getting reliable data basis, i.e. the meaning of the results; for conclusions on trace elements accumulation in deciduous tree leaves; for evaluation of species as biomonitors, and for comparisons between different biomonitoring studies as well. Acknowledgment This work was carried out within the BSEC (BLACK SEA ECONOMIC COOPERATION) Project Development Fund Grand Contract No. BSEC/PDF/0018/11.2008, and the Fundamental Science Project Nos. 141012 and 172007 funded by the Ministry of Science and Technological Development of the Republic of Serbia. References Aboal, J.R., Fernández, J.A., Carballeira, A., 2004. Oak leaves and pine needles as biomonitors of airborne trace elements pollution. Environ. Exp. Bot. 51, 215–225. Aksoy, A., Ozturk, M.A., 1997. Nerium oleander L. as a biomonitor of lead and other heavy metal pollution in Mediterranean environments. Sci. Total. Environ. 205, 145–150. Alfani, A., Maisto, G., Iovieno, P., Rutigliano, F.A., Bartoli, G., 1996. Leaf contamination by atmospheric pollutants assessed by elemental analysis of leaf tissue, leaf surface deposit and soil. J. Plant Physiol. 148, 243–248. ´ M., Spasic, ´ T., Tomaˇsevic, ´ M., Rajˇsic, ´ S., Tasic, ´ M., 2011. Trace elements accuAniˇcic, mulation and temporal trends in leaves of urban deciduous trees (Aesculus hippocastanum & Tilia spp.). Ecol. Ind. 11, 824–830. Azcue, J., Mudroch, A., 1994. Comparison of different washing, ashing, and digestion methods for the analysis of trace elements in vegetation. Int. J. Environ. Anal. Chem. 57, 151–162. Baycu, G., Tolunay, D., Ozden, H., Sureyya, G., 2006. Ecophysiological and seasonal variations in Cd, Pb, Zn and Ni concentrations in the leaves of urban deciduous trees in Istanbul. Environ. Pollut. 143, 545–554. Bargagli, R., 1998. Trace Elements in terrestrial Plants: An Ecophysiological Approach to Biomonitoring and Biorecovery. Springer-Verlag, Berlin, Heidelberg, NY. Baker, A.R., Jickells, T.D., 2006. Mineral particle size as a control on aerosol iron solubility. Geophys. Res. Lett. 33, L17608, doi:10.1029/2006GL026557. Beckett, K.P., Freer-Smith, P.H., Taylor, G., 2000. Effective tree species for local air quality management. J. Arboriculture 26, 12–19, doi:10.1016/S02697491(98)00016-25. Birmili, W., Allen, A.G., Bary, F., Harrison, R.M., 2006. Trace metal concentrations and water solubility in size-fractionated atmospheric particles and influence of road traffic. Environ. Sci. Technol. 40, 1144–1153. BSEC, 2010. Black Sea Economic Cooperation, Revitalization of urban ecosystems through vascular plants: assessment of technogenic pollution impact. Grand Contract No. BSEC/PDF/0018/11.2008, Final report. C¸elik, A., Kartal, A.A., Akdo˘gan, A., Kaska, Y., 2005. Determining the heavy metal pollution in Denizli (Turkey) by using Robinia pseudo-acacia L. Environ. Int. 31, 105–112. De Nicola, F., Maisto, G., Prati, M.V., Alfani, A., 2008. Leaf accumulation of trace elements and polycyclic aromatic hydrocarbons (PAHs) in Quercus ilex L. Environ. Pollut. 153, 376–383, doi:10.1016/j.envpol.2007.08.008. Fujiwara, F.G., Gómez, D.R., Dawidowski, L., Perelman, P., Faggie, Ana., 2011. Metals associated with airborne particulate matter in road dust and tree bark collected in a megacity (Buenos Aires, Argentina). Ecol. Ind. 11, 240–247. Lin, Z.Q., Schuepp, P.H., Schemenauer, R.S., Kennedy, G.G., 1995. Trace metal contamination in and on balsam fir (Abies balsamea L. Mill.) foliage in Southern Quebec, Canada. Water Air Soil Pollut. 81, 175–191. Liu, Y.-J., Zhu, Y.-G., Ding, H., 2007. Lead and cadmium in leaves of deciduous trees in Beijing, China: development of a metal accumulation indeh (MAI). Environ. Pollut. 145, 387–390. Luyssaert, S., 2002. Sampling procedure for the foliar analysis of deciduous trees. J. Environ. Monit. 4, 858–864. Mankovska, B., Godzik, B., Badea, O., Shiparyk, Y., Moravcik, P., 2004. Chemical and morphological characteristics of key tree species of the Carpathian Mountains. Environ. Pollut. 130, 41–54. ´ M.D., Vukˇcevic, ´ M.M., Antonovic, ´ D.G., Dimitrijevic, ´ S.I., Jovanovic, ´ Ð.M., Marjanovic, ´ M.Ð., 2009. Heavy metals concentration in soils from parks Matavulj, M.N., Ristic, and green areas in Belgrade. J. Serb. Chem. Soc. 74, 697–706. Markert, B., 1992. Establishing of “Reference Plant” for inorganic characterization of different plant species by chemical fingerprinting. Water Air Soil Pollut. 64, 533–538. Markert, B., 1993. Instrumental analysis of plants. In: Markert, B. (Ed.), Plants as Biomonitors. Indicators for Heavy Metals in Terrestrial Environment. VCH, Weinheim, pp. 65–103. Monaci, F., Moni, F., Lanciotti, E., Grechi, D., Bargagli, R., 2000. Biomonitoring of airborne metals in urban environments: new tracers of vehicle emission, in place of lead. Environ. Pollut. 107, 321–327. Nriagy, J.O., Pacyna, J.M., 1988. Quantitative assessment of worldwide contamination of air, water and soils by trace metals. Nature 333, 134–139. Onder, S., Dursun, S., 2006. Air borne heavy metal pollution of Cedrus libani (A. Rich) in the city centre of Konya (Turkey). Atmos. Environ. 40, 1122–1133.

M. Tomaˇsevi´c et al. / Ecological Indicators 11 (2011) 1689–1695 Palmieri, R.M., La Pera, L., Di Bella, G., Dugo, G., 2005. Simultaneous determination of Cd(II), Cu(II), Pb(II) and Zn(II) by derivative stripping chronopotentiometry in Pittosporum tobira leaves: a measurement of local atmospheric pollution in Messina (Sicily, Italy). Chemosphere 59, 1161–1168. Piczak, K., Lesnievicz, A., Zyrnicki, A., 2003. Metal concentrations in deciduous tree leaves from urban areas in Poland. Environ. Monit. Assess. 86, 273–287. ˇ cur, ´ ´ M., Tomaˇsevic, ´ M., Antanasijevic, ´ D., Peric-Gruji ´ ´ A., Ristic, ´ M., Su K., Aniˇcic, c, 2010. Urban deciduous tree leaves as biomonitors of trace element (As, V, and Cd) atmospheric pollution in Belgrade, Serbia. J. Serb. Chem. Soc. 75, 1453–1461. – c, ´ M., Rajˇsic, ´ S., Ðordevi ´ D., Tasic, ´ M., Krstic, ´ J., Novakovic, ´ V., 2004. Heavy Tomaˇsevic, metals accumulation in tree leaves from urban areas. Environ. Chem. Lett. 2, 151–154. ´ M., Vukmirovic, ´ Z., Rajˇsic, ´ S., Tasic, ´ M., Stevanovic, ´ B., 2005. CharacterTomaˇsevic, ization of trace metal particles deposited on some deciduous tree leaves in an urban area. Chemosphere 61, 753–760.

1695

UNECE, 2007. Manual on methods and criteria for harmonized sampling, assessment, monitoring and analysis of the effects of air pollution on forests, Part IV, Sampling and Analysis of Needles and Leaves. Weiss, P., Offenthaler, I., Öhlinger, R., Wimmer, J., 2003. Higher plants as accumulative bioindicators. In: Markert, B., Breure, A.M., Zechmeister, H.G. (Eds.), Bioindicators & Biomonitors, Principles, Concepts and Applications, vol. 6. Elsevier, Amsterdam, pp. 465–500. World Health Organization (WHO), 2003. Health aspects of air pollution with particulate matter, ozone and nitrogen dioxide. Report on a WHO Working Group, Regional Office for Europe; Bonn, Germany. EUR/03/5042688. Wyttenbach, A., Tobler, L., 1998. Effect of surface contamination on results of plant analysis. Commun. Soil. Sci. Plant Anal. 29, 809–823.