Numerous studies have been published on the radioactive contamination of lichens in European countries after the Chernobyl accident (Paatero et al. 2007; Pipiska et al. 2007; Puhakainen et al. 2007). Additionally, the main fallout radionuclides after Chernobyl accident was detected in moss, reindeers and also tea plants in Europe (LaBrecque and Cordoves 2007; Skuterud et al. 2005; Topcuoglu et al. 1997). In some studies, lichens have been used in monitoring surveys for radioactive pollution (Golubev et al. 2005; McClenahen et al. 2007; Rossbach and Lambrecht 2006). In Turkey, the observations for radioactive contamination were mostly performed in the Eastern Black Sea Region after the Chernobyl accident (Baysal and Yazıcı 1995; Gokmen et al. 1996; Köse et al. 1994; Saka et al. 1997). In past few years in the Black Sea region of Turkey, such studies have not been carried out by using lichens. In the spring–summer period of 2001, the soil-to-grass transfer of 137Cs and also its relation to several soil properties were studied in Serbia (Krstic et al. 2007).

In this paper, the levels of potassium, lead and cesium radionuclides in 12 lichen specimens collected from Trabzon and Rize in the eastern Black Sea region of Turkey were determined 20 years after the Chernobyl accident in 1986. Additionally, the data were compared with those of 1995.

Materials and Methods

After the Chernobyl accident in 1986, 14 lichen samples that were collected from Trabzon and Rize in 1995 were used to detect the radioactivity levels (Baysal and Yazıcı 1995). In this work, except for sample 8 (Xanthoria parietina) and sample 14 (Lobaria pulmonaria), the radioactivity levels in the same species collected from the same localities (Trabzon and Rize) in 2006 were re-detected to compare with those of 1995. The samples were collected from Akçaabat (Trabzon) and Çamlıhemşin (Rize) in the eastern Black Sea region of Turkey in 2006. Figure 1 shows a detailed description of all sampling sites. The soil samples were crushed thoroughly and dried at room temperature to a constant weight and later were crushed to pass through ca 2 mm mesh sieve to homogenize them.

Fig. 1
figure 1

A map showing the collecting sites

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After lichen samples (Cladonia rangiformis, C. foliacea, C. furcata, C. portentosa, Dermatocarpon miniatum, Diploschistes ocellatus, Flavoparmelia caperata, Peltigera praetextata, Xanthoria parietina and Xanthoparmelia conspersa) were separated from their substrata and were dried in an oven at 105°C for 24 h to ensure that moisture is completely removed and then were powdered. About 100 g of sample material were used and were sealed in gas tight, radon impermeable, cylindrical polyethylene plastic containers (5.5 cm diameter and 5 cm height) for gamma activity analysis. Each sample was sealed for 30 days to reach radioactive equilibrium where the decay rate of the daughters becomes equal to that of the parent. The locations, the altitudes and lichen species are given in Table 1. The radioactivity levels for lichens are given in Table 2.

Table 1 Locations, altitudes and species for the lichen specimens
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Table 2 Radioactivity levels of lichens (Bq kg− 1 dry weight)
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Gamma spectrometry measurements were done with a coaxial high purity Ge detector of 15% relative efficiency and resolution 1.9 keV at the 1,332 keV gamma of 60Co (Canberra, GC 1519 model). The detector was shielded within a 10 cm thick lead well internally lined with 2 mm Cu foils. The detector output was connected to a spectroscopy amplifier (Canberra, Model 2025). The energy calibration and relative efficiency calibration of the spectrometer were carried out using calibration sources which contained 133Ba, 57Co, 22Na, 137Cs, 54Mn, and 60Co peaks for energy range between 80 and 1,400 keV. The counting time for each sample and background was 50.000 s (Çevik et al. 2008).

The gamma ray transitions of energies 295.2, 661.6 and 1,460.8 keV were used to determine the concentration of the 212Pb, 137Cs and 40K, respectively. The activity concentrations for the natural radionuclides in the measured samples were computed using the following relation

$$ {C_s} = \frac {N_a} {\varepsilon Ptw} $$

where Cs is in (Bq kg−1), Na is the net counting rate of gamma ray, ε is the counting efficiency of the used detector, P the absolute transition of gama decay, t the counting time in seconds and w the weight of dried sample in kg. The minimum detectable activity (MDA) of the present measurement system was calculated as follows (Currie 1968)

$$ {\text{MDA}} = \frac{{\sigma {\sqrt {\text{B}} }}} {{\varepsilon Ptw}} $$

where MDA is in Bq kg−1, σ is the statistical coverage factor equal to 1.645 (confidence level 95%) and B is the background for the region of interest of a certain radionuclide. The MDA for 212Pb and 40K was 3.2 and 68.1 Bq kg−1, respectively. Since 137Cs peak was not observed in the background spectrum, the MDA for 137Cs was not calculated.

Results and Discussion

Table 2 shows that the total radioactivity is formed mainly by isotopes of natural elements, chiefly 212Pb, 40K and 137Cs, which were detected in the lichen specimens collected from Akçaabat (Trabzon) and Çamlıhemşin (Rize). The highest activities of the lichen species are seen in the locality of Helvacı (Trabzon, 100 m) and Çamlıhemşin (Rize, 1,850 m) while the activities are medium in Bozdoğan (Trabzon, 150 m), Kemaliye (Trabzon, 750 m) and Çamlihemşin (Rize, 900 m). Compared to Helvacı (Trabzon) and Çamlıhemşin (Rize, 1,850 m), medium activities of lichen species are seen in Bozdoğan (Trabzon), Kemaliye (Trabzon) and Çamlıhemşin (900 m). On the other hand, the activities of 137Cs are very low in lichen species from Arpacılı–Akçaabat (Trabzon), Helvacı village-Akçaabat (Trabzon) and Bozdoğan village-Akçaabat-Trabzon (for Cladonia furcata). According to Table 2, the activity values generally increase significantly depending on the altitudes.

Soil permeability is important for the accumulation of radionuclides into species. It is well known that the most important parameters of the permeability are rainfall, the species and the pH values of the soil. In addition, as the surfaces of the species generally increase, they accumulate more radionuclides. The highest activities of 137Cs were detected in foliose lichen species Parmotrema perlatum (Rize). The other foliose lichen species, Flavoparmelia caperata (Rize, Trabzon) and Xanthoparmelia conspersa (Trabzon), accumulate more radionuclides than the others except for Diploschistes ocellatus. The highest concentration of 137Cs was detected in samples 4, 5, 6, 7, 11. In general, foliose and fruticose species, which have much more surfaces than those of crustose, absorb and accumulate more radionuclides than the others (Baysal and Yazıcı 1995, Papastefanou et al. 1989, Pipiska et al. 2007, Puhakainen et al. 2007, Ramzaev et al. 2007). The lichens, especially foliose lichens of Parmelia, Flavoparmelia and Xanthoria, can be used as bioindicator organisms to determine the radioactive pollution (Monnet et al. 2005, Weissman et al. 2006).

Different activity values were detected in Cladonia furcata, C. portentosa, C. rangiformis, Flavoparmelia caperata and Xanthoparmelia conspersa, although they were collected from the close localities. Thus, accumulation of the radionuclides can be attributed to the kind of species, their surfaces, anatomical properties, altitudes and wind. Additionally, various amounts of rain have fallen at different places after the Chernobyl accident in 1986.

Radioactive contaminants can spread not just across countries but also across continents as it was with the Chernobyl reactor accident. Therefore, radioactive levels in the air can change each month (Papastefanou et al. 2005). The lichen samples can accumulate the radioactive contaminants from air and substrata (soil, bark, rock etc.). Since the radioactive fallout of 137Cs in the air can fall by rain and wind on different substrata, the place where the radioactive clouds and rainfall are high, more radioactive contaminants fall on lichen substrata. In this case, we noticed that the radioactive fallouts or contaminants in the air today are not very high as they were between 1986 and 1995 despite the high rainfall in Trabzon and Rize. Additionally, lichen species can reproduce permanently. It is known that young individuals can accumulate lower amounts of radioactive 137Cs and 40K. On the other hand, it must be taken into account that both different individuals (young) of the same species and radionuclides have half life. However, if the lichen specimens collected in 1995 had been kept and radioisotopes of 134Cs, 137Cs and 40K in them had been re-detected now, there might have been different radioactive levels of 134Cs, 137Cs and 40K in proportion to present levels.

Potassium is one of the most important natural isotopes. The increase in 40K radioactivity may come from two sources. The first one is connected with the natural presence of this isotope in soil, reaching 0.0119% of total potassium (UNSCEAR 1982). The highest potassium radioactivity was observed in lichen samples 5 and 9, located at Çamlıhemşin-Rize and Akçaabat-Trabzon but these values are lower than those of 1995 (Table 3). This is because of the anatomical features of Parmotrema perlatum and Xanthoria parietina. Additionally, it is thought that fine soil particles blown by winds are transported into the air and fall on the exposed parts of the plants and lichens and then were absorbed into their cells (Chibowski and Reszka 2001). Another increase of potasium concentration is connected with a long-term application of mineral fertilizing in these areas. Compared to 20 years ago, today there are not many agricultural and industrial sources hereabouts. But this kind of an agricultural area is seen in Arpacılı–Akçaabat-Trabzon, from which sample 3 and 12 were collected. Radioactive cesium isotopes 134Cs and 137Cs are very important to determine the level of the contamination of the environment. Both isotopes appear due to nuclear explosions and power plant failures. 134Cs does not cause any problems and the concentration measured for this isotope is under the detection limit of the spectrometer equipped with Ge detector (Table 2).

Table 3 Radioactivity levels of lichens in 1995 (Baysal and Yazıcı 1995)
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Since the measurements were performed 20 years after the Chernobyl accident in 1986, radionuclides of 134Cs having short half-life (2.062 y) have not been detected (L’Annunziata 2003). When the levels of the radionuclides in both studies are compared, the radioactivity levels of 137Cs and 40K in this study are significantly lower than those of 1995 (about 5.5–127 folds for 137Cs, 5–17 folds for 40K) (Fig. 2). Dangerous elements such as Cd and Cr were not detected and the level of 212Pb was acceptably small. The atmospheric fallout of 137Cs is very low in proportion to 1995 (Table 3). Therefore, the observed low activity may originate from a soil dust (Chibowski and Reszka 2001). Cesium absorbed by colloid soil particles is transported with them and may accumulate on the surfaces of the lichens. On the other hand, this isotope is kept in the heads of trees and then is washed down by rain. Therefore, lichens on barks may absorb this isotope on surfaces.

Fig. 2
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Comparison of the present amounts of 137Cs with those of 1995

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