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Quantification of transfer of 238U, 226Ra, 232Th, 40K and 137Cs in mosses of a semi-natural ecosystem
Journal of Environmental Radioactivity 101 (2010) 159–164
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Journal of Environmental Radioactivity journal homepage: www.elsevier.com/locate/jenvrad
Quantification of transfer of 238U, of a semi-natural ecosystem
226
Ra,
232
Th,
40
K and
137
Cs in mosses
S. Dragovic´ a, *, N. Mihailovic´ a, B. Gajic´ b a b
Institute for the Application of Nuclear Energy – INEP, University of Belgrade, Banatska 31b, 11080 Belgrade, Serbia Faculty of Agriculture, Institute of Land Management, Laboratory of Soil Physics, University of Belgrade, Nemanjina 6, 11081 Belgrade, Serbia
a r t i c l e i n f o
a b s t r a c t
Article history: Received 27 May 2009 Received in revised form 21 September 2009 Accepted 21 September 2009 Available online 16 October 2009
There is a lack of appropriate data on transfer of some radionuclides on many terrestrial biota groups. To expand the available data concentration ratios of 238U, 226Ra, 232Th, 40K and 137Cs in mosses are presented in this paper. The relationship between concentration ratios of radionuclides and physicochemical characteristics of the underlying soil was also investigated. The data on concentration ratios obtained here will provide a useful addition to the currently used database of transfer parameters, particularly for natural radionuclides. Ó 2009 Elsevier Ltd. All rights reserved.
Keywords: Mosses Natural radionuclides Radiocaesium Concentration ratio
1. Introduction For many years the main objective of studies conducted in the field of radioecology was to assess the impact of released radioactivity on human health, primarily through the study of agricultural food chains and the dispersion of radionuclides throughout different ecosystems. Recently a new consideration has emerged, namely the concept of protection of the environment from ionizing radiation (Burger and Gochfeld, 2001). This has increased the need to understand the transfer and behaviour of radionuclides within semi-natural habitats, to understand mechanisms of radionuclide uptake by wild species and to improve knowledge about the effects of radionuclides released into the environment as a whole. Increasing attention to radiation protection of the environment requires the assessment of radionuclide transfer to different biological species. A set of reference organisms (animals and plants) is currently used in radioecological studies in order to establish an integrated approach for radioprotection of non-human biota and their associated biotopes (Beresford et al., 2008). Due to their peculiar morphological and physiological characteristics mosses have been extensively used as bioindicators in environmental pollution studies (Steinnes, 1993; Dragovic´ et al., 2004; Gombert et al., 2004; Krommer et al., 2007). They are
* Corresponding author. Tel.: þ381 11 199 242; fax: þ381 11 2618 724. E-mail address: [email protected] (S. Dragovic´). 0265-931X/$ – see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.jenvrad.2009.09.011
distributed over large geographical areas, have a large surface-tomass ratio and are resistant against a series of substances that are highly toxic for other plants (heavy metals, radionuclides, and toxic organic compounds). As a consequence of their nutrient cycling and uptake mechanisms (most of them receive water and mineral nutrients predominantly by atmospheric deposition), they even tend to accumulate these pollutants (Zechmeister et al., 2003). The parameters needed for quantification of radionuclide transfer to biota are continually updated and are used for reconsideration of transfer factors recommended by the International Atomic Energy Agency (IAEA, 1994), which are widely employed by the scientific community, but reflect radiological data up to 1992. The aim of this study was to quantify transfer of natural (238U, 226Ra, 232 Th and 40K) and anthropogenic (137Cs) radionuclides in mosses of the Zlatibor mountain ecosystem and provide data on concentration ratios needed for revision of the currently used database. 2. Materials and methods 2.1. Study area Zlatibor is a mountain region situated in Western Serbia and represents part of the Dinarides. The mountain range spreads over an area of 300 km2, between 43 310 N, and 43 510 N, and between 19 280 E, and 19 560 E rising to an altitude between 700 and 1500 m above sea level. The air currents have blended to create a mix of Mediterranean and continental climates, so Zlatibor has a rich and diverse ecosystem consisting of more than 120 species of grass, deciduous trees (beech, oak, birch, linden and ash), while above 600 m the alpine scenery includes conifers, firs and spruce. Zlatibor mountain receives one of the highest rates of precipitation in
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S. Dragovic´ et al. / Journal of Environmental Radioactivity 101 (2010) 159–164
Serbia with a mean annual value of 960 mm (the mean annual precipitation for different areas of Serbia ranges between 600 and 1000 mm). The soils are shallow as they are derived from serpentinised peridotite residue. 2.2. Sampling Samples of mosses and underlying soils were collected from 42 sites within the Zlatibor ecosystem in Serbia during 2005 (Fig. 1). Three moss samples were taken from each site and the species collected at all sites are presented in Table 1. Green and brownish parts of mosses approximately ten years old were collected from 1 m2 plots and any adherent soil was removed. They were dried at 40 C, ground and homogenized prior to analysis. Samples (about 1 kg) of undisturbed soils up to 10 cm depth were collected from the same sites as moss samples using a stainless steel spade and a plastic scoop, and were placed immediately in plastic bags. The sampling procedure was intended to provide a representative composite sample consisting of three sub-samples from each site. Vegetation and other debris were removed from the samples, which were then dried, homogenized and passed through a 2 mm mesh sieve. 2.3. Analytical methods Soil pH was determined in distilled water and in 1 M KCl solution, in a solid– liquid (S/L) ratio of 1:2.5 ml g1. The traditional pipette method was used for particle size analysis (Rowell, 1997). Once the organic matter had been removed, the remaining mineral sample was weighed and subjected to particle size analysis to determine the following fractions: coarse sand (0.2–2 mm), fine sand (0.05– 0.2 mm), silt (0.002–0.05 mm) and clay (<0.002 mm). Organic matter (OM) content was determined by dichromate digestion based on the Walkley–Black method (Van
Table 1 Moss species collected at 42 sampling sites. Specie
Site
Scleropodium purum (Hedw.) Limpr. Pleurozium schreberi (Brid.) Mitt. Hylocomium splendens (Hedw.) Br. Eur. Hypnum cupressiforme (Hedw.) Thuidium delicatulum (Hedw.) Schimp.
1–13, 15–17, 28, 38–42 18–23, 34–37 24–27, 29 30–33 14
Reeuwijk, 1986). The total cation exchange capacity (CEC) of the sorptive complex was calculated as the sum of the hydrolytic acidity and total exchange bases, both measured according to Kappen (1929). Radioactivity measurements were performed using an HPGe gamma-ray spectrometer (ORTEC-AMETEK, 34% relative efficiency and 1.65 keV FWHM for 60Co at 1.33 MeV). The samples (composed of three sub-samples each) were then kept in hermetically sealed Marinelli beakers for about four weeks to allow equilibrium between 226Ra and its daughters and measured again for estimation of the activities of other radionuclides. Sample weight was about 0.5 kg for mosses and about 1 kg for soils and the counting time for each sample was 60 ks. The activity concentration of 238U was derived from the weighted mean of the gamma-ray lines of 234Th (63.3 and 92.8 keV), the activity concentration of 226Ra from the gamma-ray lines of 214Bi (609.3 keV) and 214Pb (295.2 and 352.0 keV), while the activity concentration of 232 Th was evaluated from the gamma-ray lines of 228Ac at 338.4, 911.1 and 968.9 keV. The activity concentrations of 40K and 137Cs were determined from their gamma-ray lines at 1460.8 keV and 661.6 keV, respectively. Gamma Vision 32 MCA emulation software was used to analyse gamma-ray spectra (ORTEC, 2001). Uncertainties of all
Fig. 1. Map showing sampling locations on Zlatibor region and position of the region within Serbia.
S. Dragovic´ et al. / Journal of Environmental Radioactivity 101 (2010) 159–164 measurements were calculated taking into account random and systematic components of uncertainty, i.e. uncertainties due to sample preparation, efficiency calibration, measurement of sample and nuclear data (Dovlete and Povinec, 2004). The uncertainties are presented at the 95% confidence level. All samples were analysed according to current laboratory QA/QC procedures involving blanks, international reference materials and spikes. To evaluate significant relationships between concentration ratios of radionuclides in mosses and soil physicochemical characteristics, Pearson’s correlation coefficients were calculated using the software package SPSS 10.0 for Windows (SPSS 10.0 for Windows). 2.4. Radionuclide transfer quantification Concentration ratios (CRs) are commonly used for quantifying and expressing uptake of radionuclides by biota. The CR is defined as the ratio of the activity concentration in biota and the activity concentration in soil: CR ¼
Activity concentration in biota ðBq kg1 dwÞ
(1)
Activity concentration in soil ðBq kg1 dwÞ
3. Results and discussion The results of radionuclide measurements in mosses reported with respect to the dry weight of the sample are presented in Table 2. The activity concentrations of natural radionuclides ranged from 1.7 to 25.1 Bq kg1 (geometric mean: 8.76 Bq kg1) for 238U, from 0.9 to 25.8 Bq kg1 (geometric mean: 6.87 Bq kg1) for 226Ra,
Table 2 Radionuclide activity concentrations (Bq kg1 d.w.) in moss samples with corresponding measuring uncertainties. Site
Altitude (m)
238
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42
980 650 710 1140 910 1011 995 1000 1015 990 1002 822 764 905 889 896 937 1002 994 662 1003 905 997 1008 1002 990 996 1102 1208 1213 911 818 903 1397 930 1003 809 1286 1097 1104 1239 1351
9.0 0.9 9.5 0.9 9.7 1.1 7.7 0.8 4.1 0.3 3.8 0.4 5.9 0.6 3.7 0.3 8.2 0.8 13.3 0.8 8.4 0.9 9.3 1.1 11.3 0.7 23.8 1.6 13.1 0.7 13.6 0.8 20.2 1.9 15.8 1.1 13.6 1.2 3.9 0.4 4.2 0.4 1.7 0.2 5.4 0.6 5.0 0.6 2.8 0.3 7.3 0.8 4.9 0.6 10.4 0.7 6.4 0.8 25.1 2.4 11.0 0.7 10.3 0.8 10.8 1.0 9.8 2.0 12.6 0.9 13.2 1.0 9.11 1.1 17.5 1.6 10.3 0.7 10.7 0.8 17.6 1.6 13.1 1.4
U
226
Ra
7.1 0.8 6.0 0.7 3.9 0.4 9.9 1.2 7.9 0.9 8.6 1.1 2.9 0.4 7.8 0.9 7.4 0.9 4.9 0.6 6.9 0.9 8.4 1.2 9.1 1.2 4.3 0.4 0.9 0.1 4.2 0.5 5.2 0.6 12.5 1.1 9.0 1.3 10.6 1.2 10.9 1.2 5.2 0.6 6.4 0.7 5.1 0.6 4.2 0.4 3.1 0.3 2.5 0.3 2.4 0.4 3.6 0.4 25.8 2.6 7.7 1.0 12.9 1.3 19.6 1.8 6.5 0.8 6.9 0.9 4.2 0.3 13.2 1.3 9.1 1.0 25.4 1.7 10.7 1.2 12.1 1.3 14.6 1.5
232
Th
3.2 0.4 3.3 0.5 2.5 0.3 3.5 0.3 2.9 0.3 3.7 0.5 1.4 0.2 4.6 1.1 3.0 0.4 4.5 0.6 3.7 0.6 2.8 0.4 5.8 0.6 6.4 0.9 5.1 0.7 4.4 0.5 5.7 0.8 4.2 0.6 3.7 0.4 4.5 0.6 4.9 0.6 3.6 0.5 4.8 0.6 2.6 0.4 3.6 0.4 0.8 0.1 2.4 0.3 3.8 1.3 3.9 0.6 13.7 2.1 12.8 1.2 6.9 0.9 9.1 1.3 13.0 1.2 4.9 0.7 3.8 0.6 4.7 0.7 8.6 1.2 4.5 0.5 6.4 0.9 4.0 0.5 5.0 0.6
40
K
172 5 244 8 165 5 247 7 213 6 214 6 44 1 231 7 202 6 236 6 214 5 258 5 101 3 193 4 158 5 127 5 203 7 287 7 152 4 232 6 238 9 157 6 128 5 208 5 96 3 165 6 48 2 292 8 124 3 301 8 129 4 288 8 275 8 213 6 117 3 186 4 140 4 250 10 692 20 290 9 263 9 197 7
137
Cs
120 4 148 6 192 8 215 6 340 10 280 8 222 8 112 4 235 5 292 8 310 8 297 8 286 8 234 6 204 6 402 12 413 10 427 12 196 6 198 8 158 5 115 4 325 8 123 4 503 14 164 5 180 6 172 5 156 5 171 6 280 8 650 20 1248 30 840 18 112 4 158 5 168 6 519 10 220 5 325 6 161 5 1115 28
161
from 0.8 to 13.7 Bq kg1 (geometric mean: 4.30 Bq kg1) for 232Th and from 44.5 to 692 Bq kg1 (geometric mean: 187 Bq kg1) for 40 K. The activity concentrations of anthropogenic 137Cs ranged from 112 to 1248 Bq kg1 with a geometric mean of 252 Bq kg1. The activity concentrations of analyzed radionuclides varied with moss species. The generally highest activity concentrations were found to be in Hypnum cupressiforme and the lowest ones in Hylocomium splendens. The total radionuclide binding is determined by the number of available exchange sites and morphological structures of the bryophytes, which differ from species to species. Therefore, most species have different uptake mechanisms (Zechmeister et al., 2003). Interspecific differences were noted in the interception and retention of airborne particulates mainly due to physical characteristics such as surface morphology and the degree of local shelter (Boileau et al., 1982). The different growth strategies lead to various levels of saturation and adsorption at different concentration intervals (Zechmeister, 1995). Additional factors, such as competition between bryophytes and higher plants, are likely to play a part (Denayer et al., 1999). The still high activity concentrations of 137Cs originating from Chernobyl fallout in mosses indicate that the runoff of this radionuclide has been relatively slow from the investigated area. Another reason for the effective uptake and long retention time of 137Cs is evidently linked to ecological factors of the area (high altitude and precipitation rate) and with physiological specificities of mosses as bioindicators (high surface-to-volume ratio). The variety of activity concentrations of this radionuclide in analyzed mosses was influenced by different altitudes of sampling sites (Table 2), interspecies differences and also by other ecological factors of sampling sites. High activity concentrations of 137Cs have been also found in mosses from other highlands in Serbia (Dragovic´ et al., 2004, 2007). The activity concentrations of radionuclides in soils collected at the same sites as the moss samples are presented in Table 3. The values for natural radionuclides ranged from 10.6 to 69.0 Bq kg1 (geometric mean: 23.2 Bq kg1) for 238U, from 8.3 to 87.5 Bq kg1 (geometric mean: 29.0 Bq kg1) for 226Ra, from 10.4 to 41.4 Bq kg1 (geometric mean: 22.5 Bq kg1) for 232Th and from 212 to 740 Bq kg1 (geometric mean: 337 Bq kg1) for 40K. The activity concentrations of 137Cs ranged from 73 to 155 Bq kg1 (geometric mean: 106 Bq kg1). In some soil samples enrichment of 226Ra with respect to 238U was identified. This could be a result of a greater mobility of uranium, leading to depleted content of this element relative to radium. It is also known that radium is more readily bound to the oxide, carbonate and exchangeable fractions, and uranium to the organic matter fraction. Therefore, soils with higher organic matter content were more available for uranium than for radium. It was also demonstrated in this study that behavior of uranium and thorium differs within the soils although these radionuclides are geologically linked (Ivanovich, 1994). Greeman and Rose (1990) studied radioactive disequilibrium in the 238U series for a number of soils and concluded that, in the surface horizons of some soils, 226Ra excess could be attributed to the cycling of 226Ra by plants, leading to an increase in this radionuclide relative to 238U. Radionuclide retention and/or mobilization by organic complexes can be the cause of the disparity between correlations of their concentrations in plants and with physicochemical characteristics of underlying soils. The CRs calculated from the activity concentrations of radionuclides in soils and mosses are presented in Table 4. The concentration ratios for 238U ranged from 0.12 to 0.69 with a geometric mean value of 0.38. These values are in accordance with those calculated for mosses collected from different locations in Canada with a mean concentration ratio of 0.30 (Sheppard et al., 2006). They also fall within the range of CR values obtained for mosses from an area with high level natural background radiation in Malaysia, which varied from 0.12 to 0.64 (Termizi Ramli et al.,
S. Dragovic´ et al. / Journal of Environmental Radioactivity 101 (2010) 159–164
162
Table 3 Radionuclide activity concentrations in soil samples (Bq kg1 d.w.) with corresponding measuring uncertainties. Site
238
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42
23.8 1.2 24.7 1.4 23.4 1.1 19.2 1.7 18.2 1.6 17.9 1.5 14.9 0.7 10.6 0.7 18.0 1.6 50.8 4.1 69.0 6.2 41.8 2.9 37.2 2.5 40.7 3.5 34.5 2.9 30.9 2.6 35.4 2.8 31.8 2.8 21.9 1.8 12.8 1.2 20.2 1.7 11.2 0.9 12.8 1.0 10.9 0.7 13.4 0.8 12.9 0.9 14.2 0.7 15.1 1.0 12.8 0.7 36.3 2.1 43.5 2.8 34.6 1.9 40.1 3.5 21.9 1.8 22.5 1.9 23.7 1.5 23.5 1.8 27.7 2.7 25.9 2.2 27.3 1.5 26.9 1.5 26.4 2.3
U
226
232
51.2 2.4 42.9 2.4 57.8 4.8 19.6 1.7 19.8 1.7 19.1 1.6 11.2 0.7 13.6 1.1 18.6 1.6 52.6 5.2 71.6 4.3 43.4 4.2 38.5 2.5 42.2 3.4 10.3 0.7 8.3 0.6 11.5 0.5 27.1 2.2 26.5 2.4 25.9 2.8 24.0 2.1 17.6 1.6 19.2 1.7 20.1 1.8 18.4 2.0 17.3 1.9 48.0 3.2 43.5 2.8 42.7 2.0 78.9 5.4 72.7 4.8 87.5 7.6 70.3 3.9 24.6 2.2 24.9 2.5 26.1 2.4 26.5 1.8 25.3 2.1 54.2 4.3 27.8 1.9 25.7 1.8 28.0 2.0
25.1 2.6 26.4 2.7 28.4 2.1 10.7 0.9 19.6 1.7 19.7 1.8 11.9 0.9 12.5 1.1 20.3 1.8 29.3 2.6 26.5 2.9 20.4 2.2 16.3 0.7 24.8 2.4 19.7 1.7 19.3 1.8 11.8 1.0 10.4 1.0 16.5 1.2 19.2 1.8 21.0 2.3 27.0 2.6 24.0 2.2 11.5 0.8 14.2 0.7 13.8 0.9 15.9 1.7 16.8 1.5 14.3 1.6 38.1 3.8 41.4 4.0 35.2 4.2 41.2 3.8 35.3 3.2 35.5 3.4 39.3 3.0 40.1 4.1 38.5 4.1 28.1 3.1 36.9 3.5 35.2 3.2 40.3 3.8
Ra
238
Th
40
137
212 6 287 7 233 6 280 6 271 6 283 7 292 7 241 6 281 6 312 6 400 12 283 6 236 5 319 6 277 6 268 6 295 7 374 8 277 6 284 7 272 7 249 6 246 6 251 6 248 6 256 6 260 7 338 7 228 6 425 10 392 8 409 10 398 10 614 18 347 7 600 16 395 12 660 20 740 16 105 4 132 5 126 5
94 2 95 2 101 3 105 3 121 3 126 3 132 3 86 2 73 2 75 2 108 3 103 3 115 3 114 3 110 3 98 2 105 3 101 3 107 3 120 3 98 2 108 3 115 3 110 3 121 4 90 3 88 2 86 2 145 4 155 4 144 4 107 3 95 2 122 3 111 3 98 2 113 3 120 3 104 3 90 2 88 2 95 2
K
Cs
2005). The values of CR for U obtained here are several-fold higher than those used in ERICA Tool (Beresford et al., 2008). To allow direct comparisons to be made, the fw/dw conversion used throughout is 0.36 for bryophytes (Beresford et al., 2008). The concentration ratio for 226Ra ranged from 0.05 to 0.57 with a geometric mean value of 0.24. Similar concentration ratios (mean of 0.30) were obtained for mosses in a Canadian survey (Sheppard et al., 2006). The values obtained in this work are lower than those obtained for mosses at a High Arctic location (Dowdall et al., 2005). They are also several-fold lower than CRs obtained for 226Ra in mosses growing in the vicinity of lignite power plants in West Macedonia, Greece (Tsikritzis et al., 2003). This study has shown that the capacity for absorption and retention of 226Ra, expressed as CR, is much higher than in vascular plants. Thorium concentration ratios in the mosses analysed here varied between 0.06 and 0.48 with a geometric mean value of 0.19. These values are lower than those obtained for the High Arctic area (Dowdall et al., 2005), but several-fold higher than the values used in ERICA Tool (Beresford et al., 2008). The concentration ratios for 40K ranged from 0.15 to 0.96 with a geometric mean value of 0.55. They fall into the range from 0.19 to 0.90 obtained for 40K concentration ratios in mosses collected in Southern Serbia (Popovic´ et al., 2008). Concentration ratios for 137Cs obtained in this study ranged from 1.01 to 13.1 with a geometric mean value of 2.39. These results are close to the value
Table 4 Concentration ratios (CRs) for Site
238
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42
0.38 0.38 0.41 0.40 0.23 0.21 0.40 0.35 0.46 0.26 0.12 0.22 0.30 0.58 0.38 0.44 0.57 0.50 0.62 0.30 0.21 0.15 0.42 0.46 0.21 0.57 0.35 0.69 0.50 0.69 0.25 0.30 0.27 0.45 0.56 0.56 0.39 0.63 0.40 0.39 0.65 0.50
238 226
U
U,
226
Ra,
232
Ra
0.14 0.14 0.07 0.51 0.40 0.45 0.26 0.57 0.40 0.09 0.10 0.19 0.24 0.10 0.09 0.51 0.45 0.46 0.34 0.41 0.45 0.30 0.33 0.25 0.23 0.18 0.05 0.06 0.08 0.33 0.11 0.15 0.28 0.26 0.28 0.16 0.50 0.36 0.47 0.38 0.47 0.52
Th,
40
232
Th
K and
137
Cs in mosses. 40
0.13 0.13 0.09 0.33 0.15 0.19 0.12 0.37 0.15 0.15 0.14 0.14 0.36 0.26 0.26 0.23 0.48 0.40 0.22 0.23 0.23 0.13 0.20 0.23 0.25 0.06 0.15 0.23 0.27 0.36 0.31 0.20 0.22 0.37 0.14 0.10 0.12 0.22 0.16 0.17 0.11 0.12
137
K
0.81 0.85 0.71 0.88 0.79 0.76 0.15 0.96 0.72 0.76 0.54 0.91 0.43 0.61 0.57 0.47 0.69 0.77 0.55 0.82 0.88 0.63 0.52 0.83 0.39 0.64 0.19 0.86 0.54 0.71 0.33 0.70 0.69 0.35 0.34 0.31 0.35 0.38 0.94 0.41 0.36 0.27
Cs
1.28 1.56 1.90 2.05 2.81 2.22 1.68 1.30 3.22 3.89 2.87 2.88 2.49 2.05 1.85 4.10 3.93 4.23 1.83 1.65 1.61 1.06 2.83 1.12 4.16 1.82 2.05 2.00 1.08 1.10 1.94 6.07 13.1 6.89 1.01 1.61 1.49 4.33 2.12 3.61 1.83 11.7
of 2.02 used in ERICA Tool (Beresford et al., 2008) but higher than those for mosses collected in Southern Serbia, which varied from 2.28 to 5.14 (Popovic´ et al., 2008). The concentration ratios of 137Cs obtained here are high due to high activity concentrations of this radionuclide in mosses which are influenced by the high precipitation rate and hence global fallout deposition for the Zlatibor area. When CRs for the different moss species analysed here are compared, it is obvious that they are species-specific (Table 5). This confirms numerous other studies which have shown interspecies differences in interception and retention of airborne particulates (Tyler, 1990; Dragovic´ et al., 2004). The average CR for 137Cs in H. cupressiforme was up to two-fold higher than that for other species. It should be noted that in assessing transfer of radionuclides to mosses the effect of age differences between moss samples was not taken into consideration.
Table 5 Concentration ratios of radionuclides (geometric mean GSD) for different moss species. Specie
238
S. purum P. schreberi H. splendens H. cupressiforme T. delicatulum
0.37 1.51 0.38 1.58 0.39 1.49 0.34 1.60 0.58
U
226
Ra
0.25 2.14 0.35 1.40 0.14 1.99 0.19 1.70 0.10
232
Th
0.18 1.56 0.19 1.61 0.17 1.90 0.26 1.33 0.26
40
137
0.60 1.60 0.51 1.49 0.46 1.78 0.58 1.46 0.61
2.58 1.65 2.00 1.83 1.80 1.73 3.62 3.05 2.05
K
Cs
S. Dragovic´ et al. / Journal of Environmental Radioactivity 101 (2010) 159–164 Table 6 Physicochemical characteristics of the analysed soils.
5.68 5.56 4.99 5.40 5.52 5.44 5.41 5.34 5.54 5.76 5.86 6.12 6.29 5.21 5.67 5.74 5.44 5.33 5.52 5.56 5.63 5.70 5.77 5.54 5.50 5.62 5.61 5.46 5.46 5.78 3.59 4.12 3.97 4.00 5.18 5.00 5.10 3.42 3.34 5.77 5.43 5.40
OM (%)
8.60 8.50 7.90 7.30 6.20 8.60 8.00 7.90 7.40 9.40 8.20 8.00 8.50 11.4 10.9 11.0 9.40 8.20 7.60 8.40 9.10 7.50 9.60 8.80 7.90 6.80 6.40 8.70 7.80 7.60 3.60 3.00 2.60 3.00 6.40 8.90 7.00 4.60 1.50 10.20 9.40 8.40
CEC (cmol kg1)
Coarse sand (%)
23.1 30.3 21.9 26.2 21.9 38.3 37.1 36.0 30.9 41.9 30.0 46.3 47.6 30.4 43.0 67.0 33.3 28.8 38.6 31.9 39.7 41.3 42.8 49.9 48.2 36.8 34.6 46.9 44.8 48.4 26.5 24.3 23.0 23.5 54.8 60.4 60.2 38.6 36.0 48.9 51.9 50.8
6.80 8.20 6.90 7.80 7.80 5.20 5.10 10.2 11.3 12.8 14.3 12.8 11.7 7.40 10.8 18.2 8.60 9.40 13.0 10.3 14.0 10.9 10.6 11.9 10.8 12.2 14.5 8.80 8.10 11.9 6.90 6.10 8.40 10.1 8.90 9.70 15.9 14.1 25.7 24.3 3.90 5.80
Fine sand (%) 6.90 6.80 4.50 7.80 7.90 6.40 7.80 14.3 9.10 18.0 17.6 16.0 10.8 8.00 8.50 20.3 8.90 8.00 22.1 18.1 18.9 8.10 8.00 14.1 16.2 10.8 16.2 7.40 6.80 8.60 7.30 7.80 5.20 7.90 7.90 8.10 22.2 22.7 28.2 27.1 6.50 3.50
Silt (%)
Clay (%)
238
72.0 70.8 69.2 63.7 70.0 71.2 66.4 58.4 69.2 54.2 59.1 56.0 61.7 63.8 60.0 48.2 62.8 70.0 57.0 62.0 58.0 68.0 61.8 59.2 60.1 62.0 50.8 67.7 65.2 68.3 73.3 70.0 65.6 72.1 76.2 76.9 41.8 54.7 39.8 39.8 78.3 69.9
14.3 14.2 19.4 20.7 14.3 17.2 20.7 17.1 10.4 15.0 9.00 15.2 15.8 20.8 20.7 13.3 19.7 12.6 7.90 9.60 9.10 13.0 19.6 14.8 12.9 15.0 18.5 16.1 19.9 11.2 12.5 16.1 20.8 9.9 7.00 5.30 20.1 8.50 6.30 8.80 11.3 20.8
Soil parameters that are expected to contribute to radionuclide uptake and transfer to mosses are presented in Table 6. Soil pH ranged from strongly acid (4.60) to near neutral (7.21). Based on the clay content, which varied from low (5.30%) to intermediate (20.8%), the soils were characterized as silty loam (USDA, 1999). Relationships between radionuclide CRs and soil parameters are shown in Table 7. Soil pH was not correlated with CRs of the radionuclides. Organic matter exhibited a positive correlation (p 0.05) with the CRs of 232Th and 137Cs. A strong positive correlation (p 0.01) was observed for CEC and the concentration ratio of 40K. No significant correlation was found between particle size distribution and radionuclide CRs, except for a positive correlation (p 0.05) between clay content and 226Ra concentration ratio. Overall, these findings are in good agreement with those obtained by Dowdall et al. (2005) for some moss species collected from a High Arctic location. The relatively weak correlation between the CRs of radionuclides in mosses and soil parameters obtained in this study emphasizes the specific uptake mechanisms of these species in respect to vascular plants. Although extensively studied the edaphic influence of the medium on radionuclide caption by mosses as well as the influence of the sampling location remain controversial. It has been shown that radionuclide uptake by mosses depends on ecological conditions at the site of their growth (Nifontova, 2000). There is also some controversy about influence of substrate on heavy
pH in water pH in KCl OM CEC Coarse sand Fine sand Silt Clay
226
U
0.314 0.256 0.134 0.278 0.116 0.128 0.122 0.249
232
Ra
0.092 0.205 0.011 0.031 0.268 0.268 0.055 0.756*
40
Th
137
K
0.063 0.040 0.191 0.517** 0.212 0.370 0.212 0.200
0.158 0.121 0.359* 0.035 0.280 0.109 0.188 0.061
Cs
0.149 0.174 0.372* 0.164 0.127 0.382 0.273 0.164
**Correlation is significant at the 0.01 level; *correlation is significant at the 0.05 level.
metals uptake by mosses. Kuik and Wolterbeek (1995) have shown some correlation of the moss metal levels with the substrate levels, implying some possible degree of contribution. Fernandez and Carballeira (2002) also demonstrated that dominant lithology in the sites where moss samples are collected has a direct influence to the concentrations of some elements. Aceto et al. (2003) demonstrated that the physiological activity of moss strictly depends on the characteristics of the growth site. Some general relationships between the concentrations of heavy metals and pedological soil types have been demonstrated (Rusco et al., 2003). These suggestions are also further supported by the fact that mosses have been known to be useful tools for geobotanical prospecting for ores on soils in which they grow (Canon, 1960; Bates and Farmer, 1992). The 137Cs and 40K activity concentrations in mosses did not exhibit any competitive relationship (Fig. 2), probably because mosses act as atmospheric filters and accumulate both radioisotopes in a directly related manner (Papastefanou et al., 1999). The absence of any correlation between activity concentrations of these radioisotopes in mosses was also demonstrated in other radioecological studies (Korobova et al., 2007; Tsikritzis et al., 2003). Our results for soil-to-moss concentration ratios underline still high persistence of radiocaesium in a semi-natural ecosystem. In these ecosystems, mosses are an important element in the total biomass. The thick carpets of mosses covering large parts of the forest soil can intercept a great quantity of the total deposition, slowing down the transfer to soil. In areas where mosses are widespread they play an important role in radiocaesium turnover. This is due to their high biomass per unit area and the rather high concentration ratio values that they usually exhibit (Fesenko et al., 2001). Mosses have large ion exchange and chelating capacities and retard the transport
1400
R = 0.309
1200 1000 -1
6.47 6.56 6.00 6.39 6.57 6.34 6.32 6.16 6.42 6.71 6.63 7.11 7.21 6.17 6.53 6.67 6.31 6.37 6.52 6.41 6.52 6.58 6.70 6.43 6.42 6.40 6.53 6.32 6.36 6.64 4.60 5.27 5.14 5.10 5.42 5.88 6.00 4.92 5.43 6.61 6.31 6.40
pH in KCL
Cs (Bq kg )
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42
pH in water
Table 7 The Pearson correlation matrix for CR of radionuclides in mosses and physicochemical characteristics of the underlying soils.
137
Site
163
800 600 400 200 0 0
100
200
300 40
Fig. 2. Correlation between
137
400
500
600
700
800
-1
K (Bq kg )
Cs and
40
K activity concentrations in mosses.
164
S. Dragovic´ et al. / Journal of Environmental Radioactivity 101 (2010) 159–164
of radionuclides under natural conditions (Tyler, 1990). In some cases, they can create a biological barrier that delays 137Cs transfer in the forest ecosystem. The elimination of radionuclides accumulated by mosses appears to be a slow process, radionuclide specific and dependent on environmental parameters (Tuominen and Jaakkola, 1973; Nimis, 1996). Increasing attention to environmental radiation protection requires the prediction of radionuclide activity concentrations in different non-human species. In order to establish predictive models the quantification of transfer of radionuclides to biota using concentration ratios is highly needed. For many reference organisms the data are dominated by radiocaesium and radiostrontium and much less data are available for natural radionuclides. The uncertainty in transfer parameters is the largest contributor to the overall uncertainty in assessments of dose to biota. The data obtained in this study will provide a useful addition, particularly for natural radionuclides, to data collected in other radioecological studies conducted during the last decade. Acknowledgements This work was funded by the Ministry of Science and Technological Development of the Republic of Serbia (Contract Nos. 142039 and 143015). References Aceto, M., Abollino, O., Conca, R., Malandrino, M., Mentasti, E., Sarzanini, C., 2003. The use of mosses as environmental metal pollution indicators. Chemosphere 50, 333–342. Bates, J.W., Farmer, A.M. (Eds.), 1992. Bryophytes and Lichens in a Changing Environment. Oxford University Press, United States of America. Beresford, N.A., Barnett, C.L., Howard, B.J., Scott, W.A., Brown, J.E., Copplestone, D., 2008. Derivation of transfer parameters for use within the ERICA-tool and the default concentration ratios for terrestrial biota. J. Environ. Radioact. 99, 1393–1407. Boileau, L.J.R., Beckett, P., Lavoie, P., Richardson, D.H.S., 1982. Lichens and mosses as monitors of industrial activity associated with uranium mining in Northern Ontario, Canada. Part 1. Environ. Pollut., Ser. B, 69–84. Burger, J., Gochfeld, M., 2001. On developing bioindicators for human and ecological health. Environ. Monit. Assess. 66, 23–46. Canon, H.L., 1960. Botanical prospecting for ore deposits. Science 132, 591–598. Denayer, F.O., Van Haluwyn, C., De Foucault, B., Schumacker, R., Colein, P., 1999. Use of bryological communities as a diagnostic tool of heavy metal soil contamination (Cd, Pb, Zn) in northern France. Plant Ecol. 140, 191–201. Dovlete, C., Povinec, P.P., 2004. Quantification of Uncertainty in Gamma-spectrometric Analysis of Environmental Samples. Quantifying Uncertainty in Nuclear Analytical Measurements. IAEA-TECDOC-1401. IAEA, Vienna. Dowdall, M., Gwynn, J.P., Moran, C., O’Dea, J., Davids, C., Lind, B., 2005. Uptake of radionuclides by vegetation at a High Arctic location. Environ. Pollut.133, 327–332. Dragovic´, S., Nedic´, O., Stankovic´, S., Bacˇic´, G., 2004. Radiocesium accumulation in mosses from highlands of Serbia and Montenegro: chemical and physiological aspects. J. Environ. Radioact. 77, 381–388. Dragovic´, S., Onjia, A., Dragovic´, R., Bacˇic´, G., 2007. Implementation of neural networks for classification of moss and lichen samples on the basis of gammaray spectrometric analysis. Environ. Monit. Assess. 130, 245–253. Fernandez, J.A., Carballeira, A., 2002. Biomonitoring metal deposition in Galicia (NW Spain) with mosse: factors affecting bioconcentration. Chemosphere 46, 535–542. Fesenko, S., Soukhova, N.V., Sanzharova, N.I., Avila, R., Spiridonov, S.I., Klein, D., Badot, P.-M., 2001. 137Cs availability for soil to understory transfer in different types of forest ecosystems. Sci. Total Environ. 269, 87–103.
Gombert, S., Rausch de Traubenberg, C., Losno, R., Leblond, S., Colin, J.L., Cossa, D., 2004. Biomonitoring of element deposition using mosses in the 2000 French survey: identifying sources and spatial trends. J. Atmos. Chem. 49, 479–502. Greeman, D.J., Rose, A.W., 1990. Form and behaviour of radium, uranium and thorium in central Pennsylvania soils derived from Dolomite. Geophys. Res. Lett. 17, 833–836. IAEA, 1994. Handbook of Parameter Values for the Prediction of Radionuclide Transfer in Temperate Environments. Technical Report Series No. 364. IAEA, Vienna. Ivanovich, M., 1994. Uranium series disequilibrium: concepts and applications. Radiochim. Acta 64, 81–94. Kappen, H., 1929. Die Bodenazidita¨t. Springer Verlag, Berlin. Korobova, E.M., Brown, J.B., Ukraintseva, N.G., Surkov, V.V., 2007. 137Cs and 40K in the terrestrial vegetation of the Yenisey Estuary: landscape, soil and plant relationships. J. Environ. Radioact. 96, 144–156. Krommer, V., Zechmeister, H.G., Roder, I., Scharf, S., Hanus-Illnar, A., 2007. Monitoring atmospheric pollutants in the biosphere reserve Wienerwald by a combined approach of biomonitoring methods and technical measurements. Chemosphere 67, 1956–1966. Kuik, P., Wolterbeek, H.T., 1995. Factor analysis of atmospheric trace-element deposition data in The Netherlands obtained by moss monitoring. Water Air Soil Pollut. 84, 323–346. Nifontova, M.G., 2000. Concentration of long-lived artificial radionuclides in the moss-lichen cover of mountain plant communities. Russ. J. Ecol. 31, 182–185. Nimis, P.L., 1996. Radiocaesium in plants of forest ecosystems. Studia Geobot. 15, 3–49. ORTEC, 2001. Gamma Vision 32, Gamma-Ray Spectrum Analysis and MCA Emulation. ORTEC, Oak Ridge. Version 5.3. Papastefanou, C., Manolopoulou, M., Stoulos, S., Ioannidou, A., Gerasopoulos, E., 1999. Soil-to-plant transfer of 137Cs, 40K and 7Be. J. Environ. Radioact. 45, 59–65. Popovic´, D., Todorovic´, D., Frontasyeva, M., Ajtic´, J., Tasic´, M., Rajsˇic´, S., 2008. Radionuclides and heavy metals in Borovac, Southern Serbia. Environ. Sci. Pollut. Res. 15, 509–520. Rowell, D.L., 1997. Bodenkunde. Untersuchungsmethoden und ihre Anwendungen. Springer, Berlin. Rusco, E., Filippi, N., Marchetti, M., Montanarella, L., 2003. Carta Ecopedologica d’Italia scala 1:250000, Relazione divulgativa a cura di: Minstero dell’Ambiente e deela Tutela Territorio. EUR 20774 IT, 45, 10 Maps and extended legend. Office of the Official Publications of the European Communities, Luxembourg. Sheppard, S.C., Sheppard, M.I., Tait, J.C., Sanipelli, B.L., 2006. Revision and metaanalysis of selected biosphere parameter values for chlorine, iodine, neptunium, radium, radon and uranium. J. Environ. Radioact. 89, 115–137. SPSS 10.0 for Windows. http://www.spss.com. Steinnes, E., 1993. Some aspects of biomonitoring of air pollutants using mosses, as illustrated by 1976 Norwegian survey. In: Markert, B. (Ed.), Plants as Biomonitors. Indicators for Heavy Metals in the Terrestrial Environment. VHC, Weinheim, pp. 381–394. Termizi Ramli, A., Wahab, M.A., Hussein, A., Khalik Wood, A., 2005. Environmental 238U and 232Th concentration measurements in an area of high level natural background radiation at Palong, Johor, Malaysia. J. Environ. Radioact. 80, 287–304. Tsikritzis, L.I., Ganatsios, S.S., Duliu, O.G., Sawidis, T.D., 2003. Natural and artificial radionuclides distribution in some lichens, mosses, and trees in the vicinity of lignite power plants from West Macedonia, Greece. J. Trace Micropr. Techn. 21, 543–554. Tuominen, Y., Jaakkola, T., 1973. Absorption and accumulation of mineral elements and radioactive nuclides. In: Ahmadjian, V., Hale, M.E. (Eds.), The Lichens. Academic Press, London, pp. 185–223. Tyler, G., 1990. Bryophytes and heavy metals: a literature review. Bot. J. Linn. Soc. 104, 231–253. USDA, 1999. Soil Taxonomy. A Basic System of Soil Classification for Making and Interpreting Soil Surveys. Handbook No. 436. Soil Survey Staff, Washington DC. Van Reeuwijk, L.P., 1986. Procedures for Soil Analysis. Technical paper 9. International Soil Reference and Information Centre (ISRIC), Wageningen, pp. 106. Zechmeister, H.G., 1995. Growth rates of five pleurocarpous moss species under various climatic conditions. J. Bryol. 18, 455–468. Zechmeister, H.G., Grodzin´ska, K., Szarek-qukaszewska, G., 2003. Bryophytes. In: Markert, B.A., Breure, A.M., Zechmeister, H.G. (Eds.), Bioindicators and Biomonitors. Elsevier Science Ltd., Amsterdam, pp. 329–375.
Contents lists available at ScienceDirect
Journal of Environmental Radioactivity journal homepage: www.elsevier.com/locate/jenvrad
Quantification of transfer of 238U, of a semi-natural ecosystem
226
Ra,
232
Th,
40
K and
137
Cs in mosses
S. Dragovic´ a, *, N. Mihailovic´ a, B. Gajic´ b a b
Institute for the Application of Nuclear Energy – INEP, University of Belgrade, Banatska 31b, 11080 Belgrade, Serbia Faculty of Agriculture, Institute of Land Management, Laboratory of Soil Physics, University of Belgrade, Nemanjina 6, 11081 Belgrade, Serbia
a r t i c l e i n f o
a b s t r a c t
Article history: Received 27 May 2009 Received in revised form 21 September 2009 Accepted 21 September 2009 Available online 16 October 2009
There is a lack of appropriate data on transfer of some radionuclides on many terrestrial biota groups. To expand the available data concentration ratios of 238U, 226Ra, 232Th, 40K and 137Cs in mosses are presented in this paper. The relationship between concentration ratios of radionuclides and physicochemical characteristics of the underlying soil was also investigated. The data on concentration ratios obtained here will provide a useful addition to the currently used database of transfer parameters, particularly for natural radionuclides. Ó 2009 Elsevier Ltd. All rights reserved.
Keywords: Mosses Natural radionuclides Radiocaesium Concentration ratio
1. Introduction For many years the main objective of studies conducted in the field of radioecology was to assess the impact of released radioactivity on human health, primarily through the study of agricultural food chains and the dispersion of radionuclides throughout different ecosystems. Recently a new consideration has emerged, namely the concept of protection of the environment from ionizing radiation (Burger and Gochfeld, 2001). This has increased the need to understand the transfer and behaviour of radionuclides within semi-natural habitats, to understand mechanisms of radionuclide uptake by wild species and to improve knowledge about the effects of radionuclides released into the environment as a whole. Increasing attention to radiation protection of the environment requires the assessment of radionuclide transfer to different biological species. A set of reference organisms (animals and plants) is currently used in radioecological studies in order to establish an integrated approach for radioprotection of non-human biota and their associated biotopes (Beresford et al., 2008). Due to their peculiar morphological and physiological characteristics mosses have been extensively used as bioindicators in environmental pollution studies (Steinnes, 1993; Dragovic´ et al., 2004; Gombert et al., 2004; Krommer et al., 2007). They are
* Corresponding author. Tel.: þ381 11 199 242; fax: þ381 11 2618 724. E-mail address: [email protected] (S. Dragovic´). 0265-931X/$ – see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.jenvrad.2009.09.011
distributed over large geographical areas, have a large surface-tomass ratio and are resistant against a series of substances that are highly toxic for other plants (heavy metals, radionuclides, and toxic organic compounds). As a consequence of their nutrient cycling and uptake mechanisms (most of them receive water and mineral nutrients predominantly by atmospheric deposition), they even tend to accumulate these pollutants (Zechmeister et al., 2003). The parameters needed for quantification of radionuclide transfer to biota are continually updated and are used for reconsideration of transfer factors recommended by the International Atomic Energy Agency (IAEA, 1994), which are widely employed by the scientific community, but reflect radiological data up to 1992. The aim of this study was to quantify transfer of natural (238U, 226Ra, 232 Th and 40K) and anthropogenic (137Cs) radionuclides in mosses of the Zlatibor mountain ecosystem and provide data on concentration ratios needed for revision of the currently used database. 2. Materials and methods 2.1. Study area Zlatibor is a mountain region situated in Western Serbia and represents part of the Dinarides. The mountain range spreads over an area of 300 km2, between 43 310 N, and 43 510 N, and between 19 280 E, and 19 560 E rising to an altitude between 700 and 1500 m above sea level. The air currents have blended to create a mix of Mediterranean and continental climates, so Zlatibor has a rich and diverse ecosystem consisting of more than 120 species of grass, deciduous trees (beech, oak, birch, linden and ash), while above 600 m the alpine scenery includes conifers, firs and spruce. Zlatibor mountain receives one of the highest rates of precipitation in
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S. Dragovic´ et al. / Journal of Environmental Radioactivity 101 (2010) 159–164
Serbia with a mean annual value of 960 mm (the mean annual precipitation for different areas of Serbia ranges between 600 and 1000 mm). The soils are shallow as they are derived from serpentinised peridotite residue. 2.2. Sampling Samples of mosses and underlying soils were collected from 42 sites within the Zlatibor ecosystem in Serbia during 2005 (Fig. 1). Three moss samples were taken from each site and the species collected at all sites are presented in Table 1. Green and brownish parts of mosses approximately ten years old were collected from 1 m2 plots and any adherent soil was removed. They were dried at 40 C, ground and homogenized prior to analysis. Samples (about 1 kg) of undisturbed soils up to 10 cm depth were collected from the same sites as moss samples using a stainless steel spade and a plastic scoop, and were placed immediately in plastic bags. The sampling procedure was intended to provide a representative composite sample consisting of three sub-samples from each site. Vegetation and other debris were removed from the samples, which were then dried, homogenized and passed through a 2 mm mesh sieve. 2.3. Analytical methods Soil pH was determined in distilled water and in 1 M KCl solution, in a solid– liquid (S/L) ratio of 1:2.5 ml g1. The traditional pipette method was used for particle size analysis (Rowell, 1997). Once the organic matter had been removed, the remaining mineral sample was weighed and subjected to particle size analysis to determine the following fractions: coarse sand (0.2–2 mm), fine sand (0.05– 0.2 mm), silt (0.002–0.05 mm) and clay (<0.002 mm). Organic matter (OM) content was determined by dichromate digestion based on the Walkley–Black method (Van
Table 1 Moss species collected at 42 sampling sites. Specie
Site
Scleropodium purum (Hedw.) Limpr. Pleurozium schreberi (Brid.) Mitt. Hylocomium splendens (Hedw.) Br. Eur. Hypnum cupressiforme (Hedw.) Thuidium delicatulum (Hedw.) Schimp.
1–13, 15–17, 28, 38–42 18–23, 34–37 24–27, 29 30–33 14
Reeuwijk, 1986). The total cation exchange capacity (CEC) of the sorptive complex was calculated as the sum of the hydrolytic acidity and total exchange bases, both measured according to Kappen (1929). Radioactivity measurements were performed using an HPGe gamma-ray spectrometer (ORTEC-AMETEK, 34% relative efficiency and 1.65 keV FWHM for 60Co at 1.33 MeV). The samples (composed of three sub-samples each) were then kept in hermetically sealed Marinelli beakers for about four weeks to allow equilibrium between 226Ra and its daughters and measured again for estimation of the activities of other radionuclides. Sample weight was about 0.5 kg for mosses and about 1 kg for soils and the counting time for each sample was 60 ks. The activity concentration of 238U was derived from the weighted mean of the gamma-ray lines of 234Th (63.3 and 92.8 keV), the activity concentration of 226Ra from the gamma-ray lines of 214Bi (609.3 keV) and 214Pb (295.2 and 352.0 keV), while the activity concentration of 232 Th was evaluated from the gamma-ray lines of 228Ac at 338.4, 911.1 and 968.9 keV. The activity concentrations of 40K and 137Cs were determined from their gamma-ray lines at 1460.8 keV and 661.6 keV, respectively. Gamma Vision 32 MCA emulation software was used to analyse gamma-ray spectra (ORTEC, 2001). Uncertainties of all
Fig. 1. Map showing sampling locations on Zlatibor region and position of the region within Serbia.
S. Dragovic´ et al. / Journal of Environmental Radioactivity 101 (2010) 159–164 measurements were calculated taking into account random and systematic components of uncertainty, i.e. uncertainties due to sample preparation, efficiency calibration, measurement of sample and nuclear data (Dovlete and Povinec, 2004). The uncertainties are presented at the 95% confidence level. All samples were analysed according to current laboratory QA/QC procedures involving blanks, international reference materials and spikes. To evaluate significant relationships between concentration ratios of radionuclides in mosses and soil physicochemical characteristics, Pearson’s correlation coefficients were calculated using the software package SPSS 10.0 for Windows (SPSS 10.0 for Windows). 2.4. Radionuclide transfer quantification Concentration ratios (CRs) are commonly used for quantifying and expressing uptake of radionuclides by biota. The CR is defined as the ratio of the activity concentration in biota and the activity concentration in soil: CR ¼
Activity concentration in biota ðBq kg1 dwÞ
(1)
Activity concentration in soil ðBq kg1 dwÞ
3. Results and discussion The results of radionuclide measurements in mosses reported with respect to the dry weight of the sample are presented in Table 2. The activity concentrations of natural radionuclides ranged from 1.7 to 25.1 Bq kg1 (geometric mean: 8.76 Bq kg1) for 238U, from 0.9 to 25.8 Bq kg1 (geometric mean: 6.87 Bq kg1) for 226Ra,
Table 2 Radionuclide activity concentrations (Bq kg1 d.w.) in moss samples with corresponding measuring uncertainties. Site
Altitude (m)
238
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42
980 650 710 1140 910 1011 995 1000 1015 990 1002 822 764 905 889 896 937 1002 994 662 1003 905 997 1008 1002 990 996 1102 1208 1213 911 818 903 1397 930 1003 809 1286 1097 1104 1239 1351
9.0 0.9 9.5 0.9 9.7 1.1 7.7 0.8 4.1 0.3 3.8 0.4 5.9 0.6 3.7 0.3 8.2 0.8 13.3 0.8 8.4 0.9 9.3 1.1 11.3 0.7 23.8 1.6 13.1 0.7 13.6 0.8 20.2 1.9 15.8 1.1 13.6 1.2 3.9 0.4 4.2 0.4 1.7 0.2 5.4 0.6 5.0 0.6 2.8 0.3 7.3 0.8 4.9 0.6 10.4 0.7 6.4 0.8 25.1 2.4 11.0 0.7 10.3 0.8 10.8 1.0 9.8 2.0 12.6 0.9 13.2 1.0 9.11 1.1 17.5 1.6 10.3 0.7 10.7 0.8 17.6 1.6 13.1 1.4
U
226
Ra
7.1 0.8 6.0 0.7 3.9 0.4 9.9 1.2 7.9 0.9 8.6 1.1 2.9 0.4 7.8 0.9 7.4 0.9 4.9 0.6 6.9 0.9 8.4 1.2 9.1 1.2 4.3 0.4 0.9 0.1 4.2 0.5 5.2 0.6 12.5 1.1 9.0 1.3 10.6 1.2 10.9 1.2 5.2 0.6 6.4 0.7 5.1 0.6 4.2 0.4 3.1 0.3 2.5 0.3 2.4 0.4 3.6 0.4 25.8 2.6 7.7 1.0 12.9 1.3 19.6 1.8 6.5 0.8 6.9 0.9 4.2 0.3 13.2 1.3 9.1 1.0 25.4 1.7 10.7 1.2 12.1 1.3 14.6 1.5
232
Th
3.2 0.4 3.3 0.5 2.5 0.3 3.5 0.3 2.9 0.3 3.7 0.5 1.4 0.2 4.6 1.1 3.0 0.4 4.5 0.6 3.7 0.6 2.8 0.4 5.8 0.6 6.4 0.9 5.1 0.7 4.4 0.5 5.7 0.8 4.2 0.6 3.7 0.4 4.5 0.6 4.9 0.6 3.6 0.5 4.8 0.6 2.6 0.4 3.6 0.4 0.8 0.1 2.4 0.3 3.8 1.3 3.9 0.6 13.7 2.1 12.8 1.2 6.9 0.9 9.1 1.3 13.0 1.2 4.9 0.7 3.8 0.6 4.7 0.7 8.6 1.2 4.5 0.5 6.4 0.9 4.0 0.5 5.0 0.6
40
K
172 5 244 8 165 5 247 7 213 6 214 6 44 1 231 7 202 6 236 6 214 5 258 5 101 3 193 4 158 5 127 5 203 7 287 7 152 4 232 6 238 9 157 6 128 5 208 5 96 3 165 6 48 2 292 8 124 3 301 8 129 4 288 8 275 8 213 6 117 3 186 4 140 4 250 10 692 20 290 9 263 9 197 7
137
Cs
120 4 148 6 192 8 215 6 340 10 280 8 222 8 112 4 235 5 292 8 310 8 297 8 286 8 234 6 204 6 402 12 413 10 427 12 196 6 198 8 158 5 115 4 325 8 123 4 503 14 164 5 180 6 172 5 156 5 171 6 280 8 650 20 1248 30 840 18 112 4 158 5 168 6 519 10 220 5 325 6 161 5 1115 28
161
from 0.8 to 13.7 Bq kg1 (geometric mean: 4.30 Bq kg1) for 232Th and from 44.5 to 692 Bq kg1 (geometric mean: 187 Bq kg1) for 40 K. The activity concentrations of anthropogenic 137Cs ranged from 112 to 1248 Bq kg1 with a geometric mean of 252 Bq kg1. The activity concentrations of analyzed radionuclides varied with moss species. The generally highest activity concentrations were found to be in Hypnum cupressiforme and the lowest ones in Hylocomium splendens. The total radionuclide binding is determined by the number of available exchange sites and morphological structures of the bryophytes, which differ from species to species. Therefore, most species have different uptake mechanisms (Zechmeister et al., 2003). Interspecific differences were noted in the interception and retention of airborne particulates mainly due to physical characteristics such as surface morphology and the degree of local shelter (Boileau et al., 1982). The different growth strategies lead to various levels of saturation and adsorption at different concentration intervals (Zechmeister, 1995). Additional factors, such as competition between bryophytes and higher plants, are likely to play a part (Denayer et al., 1999). The still high activity concentrations of 137Cs originating from Chernobyl fallout in mosses indicate that the runoff of this radionuclide has been relatively slow from the investigated area. Another reason for the effective uptake and long retention time of 137Cs is evidently linked to ecological factors of the area (high altitude and precipitation rate) and with physiological specificities of mosses as bioindicators (high surface-to-volume ratio). The variety of activity concentrations of this radionuclide in analyzed mosses was influenced by different altitudes of sampling sites (Table 2), interspecies differences and also by other ecological factors of sampling sites. High activity concentrations of 137Cs have been also found in mosses from other highlands in Serbia (Dragovic´ et al., 2004, 2007). The activity concentrations of radionuclides in soils collected at the same sites as the moss samples are presented in Table 3. The values for natural radionuclides ranged from 10.6 to 69.0 Bq kg1 (geometric mean: 23.2 Bq kg1) for 238U, from 8.3 to 87.5 Bq kg1 (geometric mean: 29.0 Bq kg1) for 226Ra, from 10.4 to 41.4 Bq kg1 (geometric mean: 22.5 Bq kg1) for 232Th and from 212 to 740 Bq kg1 (geometric mean: 337 Bq kg1) for 40K. The activity concentrations of 137Cs ranged from 73 to 155 Bq kg1 (geometric mean: 106 Bq kg1). In some soil samples enrichment of 226Ra with respect to 238U was identified. This could be a result of a greater mobility of uranium, leading to depleted content of this element relative to radium. It is also known that radium is more readily bound to the oxide, carbonate and exchangeable fractions, and uranium to the organic matter fraction. Therefore, soils with higher organic matter content were more available for uranium than for radium. It was also demonstrated in this study that behavior of uranium and thorium differs within the soils although these radionuclides are geologically linked (Ivanovich, 1994). Greeman and Rose (1990) studied radioactive disequilibrium in the 238U series for a number of soils and concluded that, in the surface horizons of some soils, 226Ra excess could be attributed to the cycling of 226Ra by plants, leading to an increase in this radionuclide relative to 238U. Radionuclide retention and/or mobilization by organic complexes can be the cause of the disparity between correlations of their concentrations in plants and with physicochemical characteristics of underlying soils. The CRs calculated from the activity concentrations of radionuclides in soils and mosses are presented in Table 4. The concentration ratios for 238U ranged from 0.12 to 0.69 with a geometric mean value of 0.38. These values are in accordance with those calculated for mosses collected from different locations in Canada with a mean concentration ratio of 0.30 (Sheppard et al., 2006). They also fall within the range of CR values obtained for mosses from an area with high level natural background radiation in Malaysia, which varied from 0.12 to 0.64 (Termizi Ramli et al.,
S. Dragovic´ et al. / Journal of Environmental Radioactivity 101 (2010) 159–164
162
Table 3 Radionuclide activity concentrations in soil samples (Bq kg1 d.w.) with corresponding measuring uncertainties. Site
238
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42
23.8 1.2 24.7 1.4 23.4 1.1 19.2 1.7 18.2 1.6 17.9 1.5 14.9 0.7 10.6 0.7 18.0 1.6 50.8 4.1 69.0 6.2 41.8 2.9 37.2 2.5 40.7 3.5 34.5 2.9 30.9 2.6 35.4 2.8 31.8 2.8 21.9 1.8 12.8 1.2 20.2 1.7 11.2 0.9 12.8 1.0 10.9 0.7 13.4 0.8 12.9 0.9 14.2 0.7 15.1 1.0 12.8 0.7 36.3 2.1 43.5 2.8 34.6 1.9 40.1 3.5 21.9 1.8 22.5 1.9 23.7 1.5 23.5 1.8 27.7 2.7 25.9 2.2 27.3 1.5 26.9 1.5 26.4 2.3
U
226
232
51.2 2.4 42.9 2.4 57.8 4.8 19.6 1.7 19.8 1.7 19.1 1.6 11.2 0.7 13.6 1.1 18.6 1.6 52.6 5.2 71.6 4.3 43.4 4.2 38.5 2.5 42.2 3.4 10.3 0.7 8.3 0.6 11.5 0.5 27.1 2.2 26.5 2.4 25.9 2.8 24.0 2.1 17.6 1.6 19.2 1.7 20.1 1.8 18.4 2.0 17.3 1.9 48.0 3.2 43.5 2.8 42.7 2.0 78.9 5.4 72.7 4.8 87.5 7.6 70.3 3.9 24.6 2.2 24.9 2.5 26.1 2.4 26.5 1.8 25.3 2.1 54.2 4.3 27.8 1.9 25.7 1.8 28.0 2.0
25.1 2.6 26.4 2.7 28.4 2.1 10.7 0.9 19.6 1.7 19.7 1.8 11.9 0.9 12.5 1.1 20.3 1.8 29.3 2.6 26.5 2.9 20.4 2.2 16.3 0.7 24.8 2.4 19.7 1.7 19.3 1.8 11.8 1.0 10.4 1.0 16.5 1.2 19.2 1.8 21.0 2.3 27.0 2.6 24.0 2.2 11.5 0.8 14.2 0.7 13.8 0.9 15.9 1.7 16.8 1.5 14.3 1.6 38.1 3.8 41.4 4.0 35.2 4.2 41.2 3.8 35.3 3.2 35.5 3.4 39.3 3.0 40.1 4.1 38.5 4.1 28.1 3.1 36.9 3.5 35.2 3.2 40.3 3.8
Ra
238
Th
40
137
212 6 287 7 233 6 280 6 271 6 283 7 292 7 241 6 281 6 312 6 400 12 283 6 236 5 319 6 277 6 268 6 295 7 374 8 277 6 284 7 272 7 249 6 246 6 251 6 248 6 256 6 260 7 338 7 228 6 425 10 392 8 409 10 398 10 614 18 347 7 600 16 395 12 660 20 740 16 105 4 132 5 126 5
94 2 95 2 101 3 105 3 121 3 126 3 132 3 86 2 73 2 75 2 108 3 103 3 115 3 114 3 110 3 98 2 105 3 101 3 107 3 120 3 98 2 108 3 115 3 110 3 121 4 90 3 88 2 86 2 145 4 155 4 144 4 107 3 95 2 122 3 111 3 98 2 113 3 120 3 104 3 90 2 88 2 95 2
K
Cs
2005). The values of CR for U obtained here are several-fold higher than those used in ERICA Tool (Beresford et al., 2008). To allow direct comparisons to be made, the fw/dw conversion used throughout is 0.36 for bryophytes (Beresford et al., 2008). The concentration ratio for 226Ra ranged from 0.05 to 0.57 with a geometric mean value of 0.24. Similar concentration ratios (mean of 0.30) were obtained for mosses in a Canadian survey (Sheppard et al., 2006). The values obtained in this work are lower than those obtained for mosses at a High Arctic location (Dowdall et al., 2005). They are also several-fold lower than CRs obtained for 226Ra in mosses growing in the vicinity of lignite power plants in West Macedonia, Greece (Tsikritzis et al., 2003). This study has shown that the capacity for absorption and retention of 226Ra, expressed as CR, is much higher than in vascular plants. Thorium concentration ratios in the mosses analysed here varied between 0.06 and 0.48 with a geometric mean value of 0.19. These values are lower than those obtained for the High Arctic area (Dowdall et al., 2005), but several-fold higher than the values used in ERICA Tool (Beresford et al., 2008). The concentration ratios for 40K ranged from 0.15 to 0.96 with a geometric mean value of 0.55. They fall into the range from 0.19 to 0.90 obtained for 40K concentration ratios in mosses collected in Southern Serbia (Popovic´ et al., 2008). Concentration ratios for 137Cs obtained in this study ranged from 1.01 to 13.1 with a geometric mean value of 2.39. These results are close to the value
Table 4 Concentration ratios (CRs) for Site
238
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42
0.38 0.38 0.41 0.40 0.23 0.21 0.40 0.35 0.46 0.26 0.12 0.22 0.30 0.58 0.38 0.44 0.57 0.50 0.62 0.30 0.21 0.15 0.42 0.46 0.21 0.57 0.35 0.69 0.50 0.69 0.25 0.30 0.27 0.45 0.56 0.56 0.39 0.63 0.40 0.39 0.65 0.50
238 226
U
U,
226
Ra,
232
Ra
0.14 0.14 0.07 0.51 0.40 0.45 0.26 0.57 0.40 0.09 0.10 0.19 0.24 0.10 0.09 0.51 0.45 0.46 0.34 0.41 0.45 0.30 0.33 0.25 0.23 0.18 0.05 0.06 0.08 0.33 0.11 0.15 0.28 0.26 0.28 0.16 0.50 0.36 0.47 0.38 0.47 0.52
Th,
40
232
Th
K and
137
Cs in mosses. 40
0.13 0.13 0.09 0.33 0.15 0.19 0.12 0.37 0.15 0.15 0.14 0.14 0.36 0.26 0.26 0.23 0.48 0.40 0.22 0.23 0.23 0.13 0.20 0.23 0.25 0.06 0.15 0.23 0.27 0.36 0.31 0.20 0.22 0.37 0.14 0.10 0.12 0.22 0.16 0.17 0.11 0.12
137
K
0.81 0.85 0.71 0.88 0.79 0.76 0.15 0.96 0.72 0.76 0.54 0.91 0.43 0.61 0.57 0.47 0.69 0.77 0.55 0.82 0.88 0.63 0.52 0.83 0.39 0.64 0.19 0.86 0.54 0.71 0.33 0.70 0.69 0.35 0.34 0.31 0.35 0.38 0.94 0.41 0.36 0.27
Cs
1.28 1.56 1.90 2.05 2.81 2.22 1.68 1.30 3.22 3.89 2.87 2.88 2.49 2.05 1.85 4.10 3.93 4.23 1.83 1.65 1.61 1.06 2.83 1.12 4.16 1.82 2.05 2.00 1.08 1.10 1.94 6.07 13.1 6.89 1.01 1.61 1.49 4.33 2.12 3.61 1.83 11.7
of 2.02 used in ERICA Tool (Beresford et al., 2008) but higher than those for mosses collected in Southern Serbia, which varied from 2.28 to 5.14 (Popovic´ et al., 2008). The concentration ratios of 137Cs obtained here are high due to high activity concentrations of this radionuclide in mosses which are influenced by the high precipitation rate and hence global fallout deposition for the Zlatibor area. When CRs for the different moss species analysed here are compared, it is obvious that they are species-specific (Table 5). This confirms numerous other studies which have shown interspecies differences in interception and retention of airborne particulates (Tyler, 1990; Dragovic´ et al., 2004). The average CR for 137Cs in H. cupressiforme was up to two-fold higher than that for other species. It should be noted that in assessing transfer of radionuclides to mosses the effect of age differences between moss samples was not taken into consideration.
Table 5 Concentration ratios of radionuclides (geometric mean GSD) for different moss species. Specie
238
S. purum P. schreberi H. splendens H. cupressiforme T. delicatulum
0.37 1.51 0.38 1.58 0.39 1.49 0.34 1.60 0.58
U
226
Ra
0.25 2.14 0.35 1.40 0.14 1.99 0.19 1.70 0.10
232
Th
0.18 1.56 0.19 1.61 0.17 1.90 0.26 1.33 0.26
40
137
0.60 1.60 0.51 1.49 0.46 1.78 0.58 1.46 0.61
2.58 1.65 2.00 1.83 1.80 1.73 3.62 3.05 2.05
K
Cs
S. Dragovic´ et al. / Journal of Environmental Radioactivity 101 (2010) 159–164 Table 6 Physicochemical characteristics of the analysed soils.
5.68 5.56 4.99 5.40 5.52 5.44 5.41 5.34 5.54 5.76 5.86 6.12 6.29 5.21 5.67 5.74 5.44 5.33 5.52 5.56 5.63 5.70 5.77 5.54 5.50 5.62 5.61 5.46 5.46 5.78 3.59 4.12 3.97 4.00 5.18 5.00 5.10 3.42 3.34 5.77 5.43 5.40
OM (%)
8.60 8.50 7.90 7.30 6.20 8.60 8.00 7.90 7.40 9.40 8.20 8.00 8.50 11.4 10.9 11.0 9.40 8.20 7.60 8.40 9.10 7.50 9.60 8.80 7.90 6.80 6.40 8.70 7.80 7.60 3.60 3.00 2.60 3.00 6.40 8.90 7.00 4.60 1.50 10.20 9.40 8.40
CEC (cmol kg1)
Coarse sand (%)
23.1 30.3 21.9 26.2 21.9 38.3 37.1 36.0 30.9 41.9 30.0 46.3 47.6 30.4 43.0 67.0 33.3 28.8 38.6 31.9 39.7 41.3 42.8 49.9 48.2 36.8 34.6 46.9 44.8 48.4 26.5 24.3 23.0 23.5 54.8 60.4 60.2 38.6 36.0 48.9 51.9 50.8
6.80 8.20 6.90 7.80 7.80 5.20 5.10 10.2 11.3 12.8 14.3 12.8 11.7 7.40 10.8 18.2 8.60 9.40 13.0 10.3 14.0 10.9 10.6 11.9 10.8 12.2 14.5 8.80 8.10 11.9 6.90 6.10 8.40 10.1 8.90 9.70 15.9 14.1 25.7 24.3 3.90 5.80
Fine sand (%) 6.90 6.80 4.50 7.80 7.90 6.40 7.80 14.3 9.10 18.0 17.6 16.0 10.8 8.00 8.50 20.3 8.90 8.00 22.1 18.1 18.9 8.10 8.00 14.1 16.2 10.8 16.2 7.40 6.80 8.60 7.30 7.80 5.20 7.90 7.90 8.10 22.2 22.7 28.2 27.1 6.50 3.50
Silt (%)
Clay (%)
238
72.0 70.8 69.2 63.7 70.0 71.2 66.4 58.4 69.2 54.2 59.1 56.0 61.7 63.8 60.0 48.2 62.8 70.0 57.0 62.0 58.0 68.0 61.8 59.2 60.1 62.0 50.8 67.7 65.2 68.3 73.3 70.0 65.6 72.1 76.2 76.9 41.8 54.7 39.8 39.8 78.3 69.9
14.3 14.2 19.4 20.7 14.3 17.2 20.7 17.1 10.4 15.0 9.00 15.2 15.8 20.8 20.7 13.3 19.7 12.6 7.90 9.60 9.10 13.0 19.6 14.8 12.9 15.0 18.5 16.1 19.9 11.2 12.5 16.1 20.8 9.9 7.00 5.30 20.1 8.50 6.30 8.80 11.3 20.8
Soil parameters that are expected to contribute to radionuclide uptake and transfer to mosses are presented in Table 6. Soil pH ranged from strongly acid (4.60) to near neutral (7.21). Based on the clay content, which varied from low (5.30%) to intermediate (20.8%), the soils were characterized as silty loam (USDA, 1999). Relationships between radionuclide CRs and soil parameters are shown in Table 7. Soil pH was not correlated with CRs of the radionuclides. Organic matter exhibited a positive correlation (p 0.05) with the CRs of 232Th and 137Cs. A strong positive correlation (p 0.01) was observed for CEC and the concentration ratio of 40K. No significant correlation was found between particle size distribution and radionuclide CRs, except for a positive correlation (p 0.05) between clay content and 226Ra concentration ratio. Overall, these findings are in good agreement with those obtained by Dowdall et al. (2005) for some moss species collected from a High Arctic location. The relatively weak correlation between the CRs of radionuclides in mosses and soil parameters obtained in this study emphasizes the specific uptake mechanisms of these species in respect to vascular plants. Although extensively studied the edaphic influence of the medium on radionuclide caption by mosses as well as the influence of the sampling location remain controversial. It has been shown that radionuclide uptake by mosses depends on ecological conditions at the site of their growth (Nifontova, 2000). There is also some controversy about influence of substrate on heavy
pH in water pH in KCl OM CEC Coarse sand Fine sand Silt Clay
226
U
0.314 0.256 0.134 0.278 0.116 0.128 0.122 0.249
232
Ra
0.092 0.205 0.011 0.031 0.268 0.268 0.055 0.756*
40
Th
137
K
0.063 0.040 0.191 0.517** 0.212 0.370 0.212 0.200
0.158 0.121 0.359* 0.035 0.280 0.109 0.188 0.061
Cs
0.149 0.174 0.372* 0.164 0.127 0.382 0.273 0.164
**Correlation is significant at the 0.01 level; *correlation is significant at the 0.05 level.
metals uptake by mosses. Kuik and Wolterbeek (1995) have shown some correlation of the moss metal levels with the substrate levels, implying some possible degree of contribution. Fernandez and Carballeira (2002) also demonstrated that dominant lithology in the sites where moss samples are collected has a direct influence to the concentrations of some elements. Aceto et al. (2003) demonstrated that the physiological activity of moss strictly depends on the characteristics of the growth site. Some general relationships between the concentrations of heavy metals and pedological soil types have been demonstrated (Rusco et al., 2003). These suggestions are also further supported by the fact that mosses have been known to be useful tools for geobotanical prospecting for ores on soils in which they grow (Canon, 1960; Bates and Farmer, 1992). The 137Cs and 40K activity concentrations in mosses did not exhibit any competitive relationship (Fig. 2), probably because mosses act as atmospheric filters and accumulate both radioisotopes in a directly related manner (Papastefanou et al., 1999). The absence of any correlation between activity concentrations of these radioisotopes in mosses was also demonstrated in other radioecological studies (Korobova et al., 2007; Tsikritzis et al., 2003). Our results for soil-to-moss concentration ratios underline still high persistence of radiocaesium in a semi-natural ecosystem. In these ecosystems, mosses are an important element in the total biomass. The thick carpets of mosses covering large parts of the forest soil can intercept a great quantity of the total deposition, slowing down the transfer to soil. In areas where mosses are widespread they play an important role in radiocaesium turnover. This is due to their high biomass per unit area and the rather high concentration ratio values that they usually exhibit (Fesenko et al., 2001). Mosses have large ion exchange and chelating capacities and retard the transport
1400
R = 0.309
1200 1000 -1
6.47 6.56 6.00 6.39 6.57 6.34 6.32 6.16 6.42 6.71 6.63 7.11 7.21 6.17 6.53 6.67 6.31 6.37 6.52 6.41 6.52 6.58 6.70 6.43 6.42 6.40 6.53 6.32 6.36 6.64 4.60 5.27 5.14 5.10 5.42 5.88 6.00 4.92 5.43 6.61 6.31 6.40
pH in KCL
Cs (Bq kg )
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42
pH in water
Table 7 The Pearson correlation matrix for CR of radionuclides in mosses and physicochemical characteristics of the underlying soils.
137
Site
163
800 600 400 200 0 0
100
200
300 40
Fig. 2. Correlation between
137
400
500
600
700
800
-1
K (Bq kg )
Cs and
40
K activity concentrations in mosses.
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S. Dragovic´ et al. / Journal of Environmental Radioactivity 101 (2010) 159–164
of radionuclides under natural conditions (Tyler, 1990). In some cases, they can create a biological barrier that delays 137Cs transfer in the forest ecosystem. The elimination of radionuclides accumulated by mosses appears to be a slow process, radionuclide specific and dependent on environmental parameters (Tuominen and Jaakkola, 1973; Nimis, 1996). Increasing attention to environmental radiation protection requires the prediction of radionuclide activity concentrations in different non-human species. In order to establish predictive models the quantification of transfer of radionuclides to biota using concentration ratios is highly needed. For many reference organisms the data are dominated by radiocaesium and radiostrontium and much less data are available for natural radionuclides. The uncertainty in transfer parameters is the largest contributor to the overall uncertainty in assessments of dose to biota. The data obtained in this study will provide a useful addition, particularly for natural radionuclides, to data collected in other radioecological studies conducted during the last decade. Acknowledgements This work was funded by the Ministry of Science and Technological Development of the Republic of Serbia (Contract Nos. 142039 and 143015). References Aceto, M., Abollino, O., Conca, R., Malandrino, M., Mentasti, E., Sarzanini, C., 2003. The use of mosses as environmental metal pollution indicators. Chemosphere 50, 333–342. Bates, J.W., Farmer, A.M. (Eds.), 1992. Bryophytes and Lichens in a Changing Environment. Oxford University Press, United States of America. Beresford, N.A., Barnett, C.L., Howard, B.J., Scott, W.A., Brown, J.E., Copplestone, D., 2008. Derivation of transfer parameters for use within the ERICA-tool and the default concentration ratios for terrestrial biota. J. Environ. Radioact. 99, 1393–1407. Boileau, L.J.R., Beckett, P., Lavoie, P., Richardson, D.H.S., 1982. Lichens and mosses as monitors of industrial activity associated with uranium mining in Northern Ontario, Canada. Part 1. Environ. Pollut., Ser. B, 69–84. Burger, J., Gochfeld, M., 2001. On developing bioindicators for human and ecological health. Environ. Monit. Assess. 66, 23–46. Canon, H.L., 1960. Botanical prospecting for ore deposits. Science 132, 591–598. Denayer, F.O., Van Haluwyn, C., De Foucault, B., Schumacker, R., Colein, P., 1999. Use of bryological communities as a diagnostic tool of heavy metal soil contamination (Cd, Pb, Zn) in northern France. Plant Ecol. 140, 191–201. Dovlete, C., Povinec, P.P., 2004. Quantification of Uncertainty in Gamma-spectrometric Analysis of Environmental Samples. Quantifying Uncertainty in Nuclear Analytical Measurements. IAEA-TECDOC-1401. IAEA, Vienna. Dowdall, M., Gwynn, J.P., Moran, C., O’Dea, J., Davids, C., Lind, B., 2005. Uptake of radionuclides by vegetation at a High Arctic location. Environ. Pollut.133, 327–332. Dragovic´, S., Nedic´, O., Stankovic´, S., Bacˇic´, G., 2004. Radiocesium accumulation in mosses from highlands of Serbia and Montenegro: chemical and physiological aspects. J. Environ. Radioact. 77, 381–388. Dragovic´, S., Onjia, A., Dragovic´, R., Bacˇic´, G., 2007. Implementation of neural networks for classification of moss and lichen samples on the basis of gammaray spectrometric analysis. Environ. Monit. Assess. 130, 245–253. Fernandez, J.A., Carballeira, A., 2002. Biomonitoring metal deposition in Galicia (NW Spain) with mosse: factors affecting bioconcentration. Chemosphere 46, 535–542. Fesenko, S., Soukhova, N.V., Sanzharova, N.I., Avila, R., Spiridonov, S.I., Klein, D., Badot, P.-M., 2001. 137Cs availability for soil to understory transfer in different types of forest ecosystems. Sci. Total Environ. 269, 87–103.
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