**1.4 Concentration ratios of K, Rb and 133Cs in soil fractions and fungi**

The concept of concentration ratios (CR, defined as concentration of the element (mg kg−1 DW) in a specific fraction or fungi divided by concentration of the element (mg kg−<sup>1</sup> DW) in bulk soil) is widely used to quantify the transfer of radionuclides from soil to plants/fungi. This approach allows the estimation of differences in uptake of elements. The elements concentration ratio data followed a similar pattern, but the enrichment of all three elements in fungal material was more evident, particularly in the sporocarps (Table 2).


Table 2. Concentration ratios CR (defined as concentration of the element (mg kg−1 DW) in the specific fraction divided by concentration of the element (mg kg−1 DW) in bulk soil) (mean values (standard deviation)).

Thus, for all three alkali metals studied, the levels of K, Rb, 133Cs and 137Cs in sporocarps were at least one order of magnitude higher than those in fungal mycelium (Table 2). The concentration ratios for each element varied considerably between the species sampled. The saprotrophic fungus *Hypholoma capnoides* had the lowest values and the mycorrhizal fungus *Sarcodon imbricatus* had the highest. Sporocarp:bulk soil concentration ratios are presented in Table 3.

*Sarcodon imbricatus* accumulates nearly 100 000 Bq kg-1 of 137Cs, giving TF values (defined as 137Cs activity concentration (Bq kg−1 DW) in fungi divided by 137Cs deposition (kBq m−2)) about 22 (Vinichuk & Johanson, 2003). The sporocarps of *Sarcodon imbricatus* had distinctively high concentration ratios of Rb and 133Cs than other species analyzed. The mycorrhizal fungus *Cantharellus tubaeformis,* is another species showing relatively high concentration ratios, particularly for K and Rb. *Cantharellus tubaeformis* accumulates several tens of thousands Bq kg-1 of 137Cs (Kammerer et al., 1994). Among those with moderate concentration ratios for each element are *Boletus edulis, Tricholoma equestre, Lactarius scrobiculatus* and *Cortinarius* spp.

Thus, the levels of K, Rb, 133Cs and 137Cs in sporocarps were at least one order of magnitude higher than those in fungal mycelium indicating biomagnification through the food web in forest ecosystems.

amount of unavailable 133Cs, compared to the total amount of 133Cs, in soil presumably higher than that of 137Cs. As a result, stable 133Cs is considered less available for uptake as it is contained in mineral compounds and is difficult for fungi or plants to access: the concentration ratio of stable 133Cs in mushrooms is lower than for 137Cs (Yoshida & Muramatsu, 1998). The differing behavior of the natural and radioactive forms of 133Cs may

The concept of concentration ratios (CR, defined as concentration of the element (mg kg−1 DW) in a specific fraction or fungi divided by concentration of the element (mg kg−<sup>1</sup> DW) in bulk soil) is widely used to quantify the transfer of radionuclides from soil to plants/fungi. This approach allows the estimation of differences in uptake of elements. The elements concentration ratio data followed a similar pattern, but the enrichment of all three elements in fungal material was more evident, particularly in the sporocarps

Element Rhizosphere Soil root-interface Fungal mycelium Fruit bodies

K 1.7 (0.4) 6.1 (1.9) 5.1 (1.4) 68.9 (23.1)

Cs 1.1 (0.5) 0.8 (0.3) 2.1 (0.9) 39.7 (67.6)

Rb 1.3 (0.4) 2.7 (1.1) 3.9 (1.1) 121.7 (172.2)

Table 2. Concentration ratios CR (defined as concentration of the element (mg kg−1 DW) in the specific fraction divided by concentration of the element (mg kg−1 DW) in bulk soil)

Thus, for all three alkali metals studied, the levels of K, Rb, 133Cs and 137Cs in sporocarps were at least one order of magnitude higher than those in fungal mycelium (Table 2). The concentration ratios for each element varied considerably between the species sampled. The saprotrophic fungus *Hypholoma capnoides* had the lowest values and the mycorrhizal fungus *Sarcodon imbricatus* had the highest. Sporocarp:bulk soil concentration ratios are presented in

*Sarcodon imbricatus* accumulates nearly 100 000 Bq kg-1 of 137Cs, giving TF values (defined as 137Cs activity concentration (Bq kg−1 DW) in fungi divided by 137Cs deposition (kBq m−2)) about 22 (Vinichuk & Johanson, 2003). The sporocarps of *Sarcodon imbricatus* had distinctively high concentration ratios of Rb and 133Cs than other species analyzed. The mycorrhizal fungus *Cantharellus tubaeformis,* is another species showing relatively high concentration ratios, particularly for K and Rb. *Cantharellus tubaeformis* accumulates several tens of thousands Bq kg-1 of 137Cs (Kammerer et al., 1994). Among those with moderate concentration ratios for each element are *Boletus edulis, Tricholoma equestre,*

Thus, the levels of K, Rb, 133Cs and 137Cs in sporocarps were at least one order of magnitude higher than those in fungal mycelium indicating biomagnification through the food web in

derive from their disequilibrium in the ecosystem (Horyna & Řanad, 1988).

**1.4 Concentration ratios of K, Rb and 133Cs in soil fractions and fungi** 

(Table 2).

Table 3.

forest ecosystems.

(mean values (standard deviation)).

*Lactarius scrobiculatus* and *Cortinarius* spp.


1Saprophyte, all other analyzed fungal species are ectomycorrhizal

Table 3. Element concentration ratios (mg kg−1 DW in fungi)/(mg kg−1 DW in bulk soil) in fungi for fungal sporocarps.

#### **1.5 Relationships between K, Rb and 133Cs in soil and fungi**

Although correlation analysis may be not definitive, it is a useful approach for elucidating similarities or differences in uptake mechanisms of cesium (137Cs and 133Cs), K and Rb: close correlation between elements indicates similarities in their uptake mechanisms. No significant correlations between K in soil and in either mycelium (r=0.452, ns) or in sporocarps (r=0.338, ns) has been identified and sporocarp Rb and 133Cs concentrations were unrelated to soil concentrations, however, in mycelium both elements were correlated with soil concentrations (Rb: r=0.856, p=0.003; Cs: r=0.804, p=0.009). There was a close positive correlation (r=0.946, p=0.001) between the K:Rb ratio in soil and in fungal mycelium (Figure 1b) and this relationship was also apparent between soil and sporocarps, but was weak and not significant (r=0.602, ns: Figure1b).

The K:133Cs ratio in soil and fungal components had a different pattern: the K:Cs ratio in mycelium was closely positively correlated (r=0.883, p=0.01) to the K:133Cs ratio in soil (Figure 1a), but was relatively weakly and non-significantly correlated to soil in fungal sporocarps. No significant correlations were found between the concentrations of the three elements in fungi, soil pH or soil organic matter content (data not shown).

The competition between K, Rb and 133Cs in the various transfer steps was investigated in an attempt to estimate the relationships between the concentrations of these three elements in soil, mycelia and fungal sporocarps. The lack of a significant correlation between K in soil and in either mycelium or sporocarps indicated a demand for essential K in fungi, regardless of the concentration of this element in soil. Regardless of fungal species, K concentration in fungi appears to be controlled within a narrow range, (Yoshida & Muramatsu, 1998), and supports the claim K uptake by fungi is self-regulated by the internal nutritional requirements of the fungus (Baeza et al., 2004).

Cesium (137Cs and 133Cs), Potassium

Vinichuk et al.

Vinichuk et al.

Yoshida & Muramatsu (1998), Japan

Yoshida & Muramatsu (1998), Japan

and Rubidium in Macromycete Fungi and *Sphagnum* Plants 289

study (Vinichuk et al., 2010b) were calculated and compared with estimates calculated in similar studies by Yoshida & Muramatsu (1998). Mean values of isotopic ratios of 137Cs/K, 137Cs/Rb and 137Cs/133Cs in the fungal sporocarps, and range and correlation coefficients between concentration ratios 137Cs/133Cs and K, Rb and 133Cs are presented in Table 4.

(2010b), Sweden 12 14.4(1.54−45.4)x10−13 7.8(0.55−30.9)x10−<sup>10</sup> 4.9(0.30−15.1)x10−<sup>8</sup>

29 0.12 0.39 0.26

137Cs/K 137Cs/Rb 137Cs/133Cs

29 5.2(0.15−23.0)x10−16 3.4(0.14−18.2)x10−<sup>13</sup> 4.1(1.53−5.94)x10−<sup>9</sup>

137Cs/133Cs:K 137Cs/133Cs:Rb 137Cs/133Cs:133Cs

Data set n Isotopic ratios

Correlation coefficients

sporocarps (n = number of sporocarps analyzed).

forest soil (Rühm et al., 1997; Karadeniz & Yaprak, 2007).

between fungi, their host and the environment.

(2010b), Sweden 12 0.25 −0.35 −0.31

Table 4. Isotopic (atom) ratios of 137Cs/K, 137Cs/Rb, 137Cs/133Cs, correlation coefficients between isotopic ratios 137Cs/133Cs and mass concentrations of K, Rb and 133Cs in fungal

The activity concentrations of 137Cs in fungal sporocarps were about 13 to 16 orders of magnitude lower than mass concentrations of K, 10 to 13 orders of magnitude lower than mass concentrations for Rb, and 8 to 9 orders of magnitude lower than mass concentrations for 133Cs. Isotopic (atom) ratios in the fungal sporocarps collected in Sweden were two-three orders of magnitude narrower than those collected in Japan, which reflected the level of 137Cs concentrations in mushrooms: the median value for all fungi species was 4151 Bq kg−1 DW in Swedish forests and 135 Bq kg−1 DW in Japanese forests. Isotopic (atom) ratios of 137Cs/K, 137Cs/Rb, 137Cs/133Cs were variable in both datasets and appeared independent of specific species of fungi. These ratios might reflect the isotopic ratios of soil horizons from which radiocesium is predominantly taken up and be a possible source of the variability in isotopic ratios in fungal fruit bodies. Rühm et al. (1997) used the isotopic ratio 134Cs/137Cs to localize mycelia of fungal species *in situ*; alternatively, the isotopic (atom) ratio 137Cs/133Cs can be used to localize fungal mycelia *in situ*. However, this approach is only appropriate for organic soil layers, which contain virtually no or very little clay mineral to which cesium can bind. The isotopic ratios 137Cs/133Cs in fruit bodies of fungi were similar to those found in organic soil layers of

The relationships observed between the concentration ratios 137Cs/133Cs and K, Rb and 133Cs in fungal sporocarps also varied widely and were inconsistent (Table 4). The concentration of K, Rb and 133Cs in sporocarps appeared independent of the 137Cs/133Cs isotopic ratio, suggesting differences in uptake of these alkali metals by fungi and complex interactions

Fig. 1**.** Ratio of (a) K: 133Cs and (b) K:Rb in fungal sporocarps (♦, solid line) and soil mycelium (○, dotted line) in relation to the soil in which they were growing. \*\* p=0.01, \*\*\* p=0.001

The relationships observed between K:Rb and K:133Cs ratios in fungal sporocarps and soil mycelia, with respect to the soil in which they were growing (Figure 1), also indicated differences in uptake of these alkali metals by fungi. Although correlation analyses is not the best tool for analyzing the uptake mechanism, the closest positive correlations between K:Rb ratios in fungal mycelium and in soil indicated similarities in the uptake mechanism of these two elements by fungi, although the relationships between K: 133Cs ratios in soil mycelium and in soil were less pronounced. These findings were in good agreement with the suggestion by Yoshida & Muramatsu (1998) that there might be an alternative pathway for 133Cs uptake into cells and the mechanism of 133Cs uptake by fungi could be similar to that for Rb, as 133Cs does not show a good correlation with K. The high efficiency of Rb uptake by fungi indicates Rb, but not 133Cs, eventually replaces essential K due to K limitation (Brown & Cummings, 2001) and Rb has the capacity to partially replace K, but 133Cs does not (Wallace, 1970 and references therein). Forest plants apparently discriminate between K+ and Rb+ in soils and a shortage of K+ favors the uptake of the closely related Rb+ ion (Nyholm & Tyler, 2000), whereas, increasing K+ availability in the system decreases Rb+ uptake (Drobner & Tyler, 1998). These results provided new insights into the use of transfer factors or concentration ratios.

#### **1.6 The isotopic (atom) ratios 137Cs/K, 137Cs/Rb and 137Cs/133Cs in fungal species**

The isotopic ratios of 137Cs/K, 137Cs/Rb and 137Cs/133Cs in the fungal sporocarps belonging to different species were used to interpret the distribution of 137Cs and the alkali metals in fungi and to provide better understanding of its uptake mechanisms. Measurements of trace levels of stable 133Cs could be another way of obtaining information about the biological behavior of 137Cs. To obtain better estimates, the isotopic ratios for fungal sporocarps in this

b

y = 0.431x + 102.4 r = 0.602 ns

0 100 200 300 400 500 K:Rb ratio in soil

y = 0.902x + 54.88 r = 0.946\*\*\*

a

Fig. 1**.** Ratio of (a) K: 133Cs and (b) K:Rb in fungal sporocarps (♦, solid line) and soil mycelium (○, dotted line) in relation to the soil in which they were growing. \*\* p=0.01, \*\*\* p=0.001

0

100

200

300

K:Rb ratio in fungi

400

500

y = 2.185x + 0.176 r = 0.883\*\*

)

y = 4.636x + 0.481 r = 0.752 ns

0 2 4 6 8 10 K:Cs ratio in soil (x 10<sup>3</sup>

The relationships observed between K:Rb and K:133Cs ratios in fungal sporocarps and soil mycelia, with respect to the soil in which they were growing (Figure 1), also indicated differences in uptake of these alkali metals by fungi. Although correlation analyses is not the best tool for analyzing the uptake mechanism, the closest positive correlations between K:Rb ratios in fungal mycelium and in soil indicated similarities in the uptake mechanism of these two elements by fungi, although the relationships between K: 133Cs ratios in soil mycelium and in soil were less pronounced. These findings were in good agreement with the suggestion by Yoshida & Muramatsu (1998) that there might be an alternative pathway for 133Cs uptake into cells and the mechanism of 133Cs uptake by fungi could be similar to that for Rb, as 133Cs does not show a good correlation with K. The high efficiency of Rb uptake by fungi indicates Rb, but not 133Cs, eventually replaces essential K due to K limitation (Brown & Cummings, 2001) and Rb has the capacity to partially replace K, but 133Cs does not (Wallace, 1970 and references therein). Forest plants apparently discriminate between K+ and Rb+ in soils and a shortage of K+ favors the uptake of the closely related Rb+ ion (Nyholm & Tyler, 2000), whereas, increasing K+ availability in the system decreases Rb+ uptake (Drobner & Tyler, 1998). These results provided new insights into the use of transfer

**1.6 The isotopic (atom) ratios 137Cs/K, 137Cs/Rb and 137Cs/133Cs in fungal species**  The isotopic ratios of 137Cs/K, 137Cs/Rb and 137Cs/133Cs in the fungal sporocarps belonging to different species were used to interpret the distribution of 137Cs and the alkali metals in fungi and to provide better understanding of its uptake mechanisms. Measurements of trace levels of stable 133Cs could be another way of obtaining information about the biological behavior of 137Cs. To obtain better estimates, the isotopic ratios for fungal sporocarps in this

factors or concentration ratios.

0

10

20

30

K:Cs ratio in fungi (x 103

)

40

50

60


Table 4. Isotopic (atom) ratios of 137Cs/K, 137Cs/Rb, 137Cs/133Cs, correlation coefficients between isotopic ratios 137Cs/133Cs and mass concentrations of K, Rb and 133Cs in fungal sporocarps (n = number of sporocarps analyzed).

The activity concentrations of 137Cs in fungal sporocarps were about 13 to 16 orders of magnitude lower than mass concentrations of K, 10 to 13 orders of magnitude lower than mass concentrations for Rb, and 8 to 9 orders of magnitude lower than mass concentrations for 133Cs. Isotopic (atom) ratios in the fungal sporocarps collected in Sweden were two-three orders of magnitude narrower than those collected in Japan, which reflected the level of 137Cs concentrations in mushrooms: the median value for all fungi species was 4151 Bq kg−1 DW in Swedish forests and 135 Bq kg−1 DW in Japanese forests. Isotopic (atom) ratios of 137Cs/K, 137Cs/Rb, 137Cs/133Cs were variable in both datasets and appeared independent of specific species of fungi. These ratios might reflect the isotopic ratios of soil horizons from which radiocesium is predominantly taken up and be a possible source of the variability in isotopic ratios in fungal fruit bodies. Rühm et al. (1997) used the isotopic ratio 134Cs/137Cs to localize mycelia of fungal species *in situ*; alternatively, the isotopic (atom) ratio 137Cs/133Cs can be used to localize fungal mycelia *in situ*. However, this approach is only appropriate for organic soil layers, which contain virtually no or very little clay mineral to which cesium can bind. The isotopic ratios 137Cs/133Cs in fruit bodies of fungi were similar to those found in organic soil layers of forest soil (Rühm et al., 1997; Karadeniz & Yaprak, 2007).

The relationships observed between the concentration ratios 137Cs/133Cs and K, Rb and 133Cs in fungal sporocarps also varied widely and were inconsistent (Table 4). The concentration of K, Rb and 133Cs in sporocarps appeared independent of the 137Cs/133Cs isotopic ratio, suggesting differences in uptake of these alkali metals by fungi and complex interactions between fungi, their host and the environment.

Cesium (137Cs and 133Cs), Potassium

study's different genotypes.

M = mean, CV = coefficient of variation.

correlated in the combined dataset (Figure 2: f).

within the whole population or among the genotypes.

the forth was only moderately correlated (Table 7).

concentrations (Figure 3: a, c, b).

cesium (137Cs and 133Cs) and K.

(Table 7).

Sitegenotype1

and Rubidium in Macromycete Fungi and *Sphagnum* Plants 291

sporocarps 2-1 2-2 4-3 4-4 4-5 4-6 7-7 6-8

Unidentified genotypes

Combined set of

Identified genotypes

M 1.67 1.43 3.16 3.95 2.86 2.43 3.27 2.24 2.62 2.50

CV (%) 97.1 36.4 10.4 5.1 78.1 29.5 9.2 3.9 20.0 34.6

1Site numbering according to Dahlberg et al. (1997), the second figure is a running number of the

Table 6. 137Cs/133Cs isotopic (atom) ratios in sporocarps of *S. variegatus* from identified genotypes, with unknown genetic belonging, and the two combined groupings, x10−7.

Similarly, in results obtained from a previous study (Vinichuk et al. 2004) the concentrations of K in sporocarps of *S. variegatus* were not related to the concentrations of 137Cs (r=0.103) or 133Cs (r=−0.066) in the combined data set (Figure 2: c, b). In contrast, the concentrations of K

Rubidium was strongly correlated with stable 133Cs (r=0.746) and moderately correlated with 137Cs (r=0.440) and K (r=0.505: Figure 2: d, e, a). Both 133Cs and 137Cs were significantly

The 137Cs/133Cs isotopic ratio in the combined dataset was not correlated to K concentration, but correlated moderately and negatively with both 133Cs (r=−0.636) and Rb (r=−0.500)

Thus, the study of *S. variegatus* revealed no significant correlations between 133Cs mass concentration or 137Cs activity concentration and the concentration of K in sporocarps, either

Potassium, 133Cs and 137Cs within the four genotypes were also not correlated, with one genotype exception (Table 7). However, the exception was conditional due to a one single value. Three of four analyzed sporocarp genotypes had high correlation between K and Rb:

However, the correlations between 137Cs and K and Rb and 133Cs in the four genotypes were inconsistent (Table 3). Potassium, Rb, 133Cs and 137Cs were correlated in genotype 2-1 (due to one single value), whereas, no or negative correlations were found between the same elements/isotopes for the other three genotypes. In two of four genotypes, the 137Cs/133Cs isotopic ratio was not correlated with 133Cs, K or Rb; however, there was a negative correlation with Rb in one genotype (2-2) and positive correlation with 133Cs in another (4-3)

Data obtained for *S. variegatus* supported results from earlier studies (Ismail, 1994; Yoshida & Muramatsu, 1998) on different species of fungi, suggesting cesium (137Cs and 133Cs) and K are not correlated in mushrooms. Thus, correlation analysis may be a useful, although not definitive, approach for elucidating similarities or differences in uptake mechanisms of

and Rb were significantly correlated in the combined dataset (r=0.505, Figure 2: a).

#### **1.7 K, Rb and Cs (137Cs and 133Cs) in sporocarps of a single species**

Most results presented in this Chapter are already published (Vinichuk et al., 2011), and are based on sporocarp analysis of different ectomycorrhizal and saprotrophic fungal species. Fungal accumulation of 137Cs is suggested to be species-dependent, thus, 137Cs activity concentration and mass concentration of K, Rb and 133Cs in fungal sporocarps belonging to the mycorrhizal fungus *Suillus variegatus* were analyzed*. S. variegatus* form *mycorrhiza* with Scots pine and predominantly occur in sandy, acidic soils and have a marked ability to accumulate radiocesium (Dahlberg et al., 1997): as this is an edible mushroom, high radiocesium contents present some concern with regard to human consumption.

The concentrations of K (range 22.2-52.1 g kg−1) and Rb (range 0.22-0.65 g kg−1) in sporocarps of *S. variegatus* varied in relatively narrow ranges, whereas, the mass concentration of 133Cs had a range of 2.16 to 21.5 mg kg−1 and the activity concentration of 137Cs ranged from 15.8 to 150.9 kBq kg−1. Both 133Cs and 137Cs had wider ranges than K or Rb within sporocarps from the same genotype or across the combined set of sporocarps (Table 5). The mean of the 137Cs/133Cs isotopic ratio in the combined set of sporocarps was 2.5 x 10−7 (range 8.3 x 10−8 and 4.4 x 10−7). The 137Cs/Cs isotopic ratios from identified genotypes were site-genotype dependent: the ratio values of genotypes at site 4 were about two-times higher than the ratios of genotypes at site 2 (Table 6).


1Site numbering according to Dahlberg et al. (1997), the second figure is a running number of the study's different genotypes.

Table 5. Potassium, rubidium and cesium (133Cs) mass concentrations and 137Cs activity concentrations in sporocarps of *S. variegatus* (DW) from identified and unknown genotypes, where n = number of sporocarps of each genotype analyzed, M = mean, SD = standard deviation, CV = coefficient of variation.

Most results presented in this Chapter are already published (Vinichuk et al., 2011), and are based on sporocarp analysis of different ectomycorrhizal and saprotrophic fungal species. Fungal accumulation of 137Cs is suggested to be species-dependent, thus, 137Cs activity concentration and mass concentration of K, Rb and 133Cs in fungal sporocarps belonging to the mycorrhizal fungus *Suillus variegatus* were analyzed*. S. variegatus* form *mycorrhiza* with Scots pine and predominantly occur in sandy, acidic soils and have a marked ability to accumulate radiocesium (Dahlberg et al., 1997): as this is an edible mushroom, high

The concentrations of K (range 22.2-52.1 g kg−1) and Rb (range 0.22-0.65 g kg−1) in sporocarps of *S. variegatus* varied in relatively narrow ranges, whereas, the mass concentration of 133Cs had a range of 2.16 to 21.5 mg kg−1 and the activity concentration of 137Cs ranged from 15.8 to 150.9 kBq kg−1. Both 133Cs and 137Cs had wider ranges than K or Rb within sporocarps from the same genotype or across the combined set of sporocarps (Table 5). The mean of the 137Cs/133Cs isotopic ratio in the combined set of sporocarps was 2.5 x 10−7 (range 8.3 x 10−8 and 4.4 x 10−7). The 137Cs/Cs isotopic ratios from identified genotypes were site-genotype dependent: the ratio values of genotypes at site 4 were about

2-1 8 30.6 8.06 26.4 0.47 0.12 24.7 12.1 4.23 35.1 67.3 35.1 52.2 2-2 6 28.0 6.99 25.0 0.50 0.07 13.8 16.6 2.19 13.2 75.9 23.2 30.6 4-3 4 28.5 2.13 7.5 0.39 0.16 4.0 6.6 0.44 6.7 68.9 11.7 17.0 4-4 3 33.6 8.60 - 0.30 0.04 - 3.0 0.60 - 39.1 9.38 - 4-5 2 38.9 2.40 - 0.36 0.02 - 3.8 0.04 - 35.7 28.2 - 4-6 2 35.2 8.84 - 0.37 0.11 - 3.7 2.16 - 26.8 8.54 - 7-7 5 33.7 5.79 17.2 0.34 0.06 17.9 6.7 0.80 12.0 71.4 9.30 13.0 6-8 2 25.4 1.34 - 0.31 0.03 - 8.7 2.16 - 63.3 18.3 -

19 33.4 6.69 20.0 0.38 0.08 20.3 7.7 1.97 25.5 66.0 21.3 32.3

 51 31.9 6.79 21.3 0.40 0.09 23.6 8.7 4.36 50.1 63.7 24.2 38.0 1Site numbering according to Dahlberg et al. (1997), the second figure is a running number of the

Table 5. Potassium, rubidium and cesium (133Cs) mass concentrations and 137Cs activity concentrations in sporocarps of *S. variegatus* (DW) from identified and unknown genotypes, where n = number of sporocarps of each genotype analyzed, M = mean, SD = standard

Combined set of sporocarps (identified and unknown genotypes)

K Rb 133Cs 137Cs g kg−1 % g kg−1 % mg kg−1 % kBq kg−1 % M SD CV M SD CV M SD CV M SD CV

**1.7 K, Rb and Cs (137Cs and 133Cs) in sporocarps of a single species**

radiocesium contents present some concern with regard to human consumption.

two-times higher than the ratios of genotypes at site 2 (Table 6).

Site-

genotype1 <sup>n</sup>

Sporocarps with identified genotypes

Sporocarps with unknown genotypes

deviation, CV = coefficient of variation.

study's different genotypes.


1Site numbering according to Dahlberg et al. (1997), the second figure is a running number of the study's different genotypes.

Table 6. 137Cs/133Cs isotopic (atom) ratios in sporocarps of *S. variegatus* from identified genotypes, with unknown genetic belonging, and the two combined groupings, x10−7. M = mean, CV = coefficient of variation.

Similarly, in results obtained from a previous study (Vinichuk et al. 2004) the concentrations of K in sporocarps of *S. variegatus* were not related to the concentrations of 137Cs (r=0.103) or 133Cs (r=−0.066) in the combined data set (Figure 2: c, b). In contrast, the concentrations of K and Rb were significantly correlated in the combined dataset (r=0.505, Figure 2: a).

Rubidium was strongly correlated with stable 133Cs (r=0.746) and moderately correlated with 137Cs (r=0.440) and K (r=0.505: Figure 2: d, e, a). Both 133Cs and 137Cs were significantly correlated in the combined dataset (Figure 2: f).

The 137Cs/133Cs isotopic ratio in the combined dataset was not correlated to K concentration, but correlated moderately and negatively with both 133Cs (r=−0.636) and Rb (r=−0.500) concentrations (Figure 3: a, c, b).

Thus, the study of *S. variegatus* revealed no significant correlations between 133Cs mass concentration or 137Cs activity concentration and the concentration of K in sporocarps, either within the whole population or among the genotypes.

Potassium, 133Cs and 137Cs within the four genotypes were also not correlated, with one genotype exception (Table 7). However, the exception was conditional due to a one single value. Three of four analyzed sporocarp genotypes had high correlation between K and Rb: the forth was only moderately correlated (Table 7).

However, the correlations between 137Cs and K and Rb and 133Cs in the four genotypes were inconsistent (Table 3). Potassium, Rb, 133Cs and 137Cs were correlated in genotype 2-1 (due to one single value), whereas, no or negative correlations were found between the same elements/isotopes for the other three genotypes. In two of four genotypes, the 137Cs/133Cs isotopic ratio was not correlated with 133Cs, K or Rb; however, there was a negative correlation with Rb in one genotype (2-2) and positive correlation with 133Cs in another (4-3) (Table 7).

Data obtained for *S. variegatus* supported results from earlier studies (Ismail, 1994; Yoshida & Muramatsu, 1998) on different species of fungi, suggesting cesium (137Cs and 133Cs) and K are not correlated in mushrooms. Thus, correlation analysis may be a useful, although not definitive, approach for elucidating similarities or differences in uptake mechanisms of cesium (137Cs and 133Cs) and K.

Cesium (137Cs and 133Cs), Potassium

137Cs/ a 133Cs:K

0.0

1.0

2.0

137Cs/133Cs

3.0

4.0

5.0

and Rubidium in Macromycete Fungi and *Sphagnum* Plants 293

137Cs/Cs:133Cs c

0.0

y = -1E-08x + 4E-07; r = −0.636\*\*\*

1.0

2.0

137Cs/133Cs

3.0

4.0

5.0

y = -5E-07x + 4E-07; r = −0.500\*\*\*

Rb, g kg-1

0.2 0.4 0.6

137Cs/133Cs:Rb b

y = 2E-09x + 2E-07; r = 0.181

10 20 30 40 50 60

K, g kg-1

Fig. 3. Relationship between the 137Cs/133Cs isotopic (atom) ratios (x10−7) and K, Rb and 133Cs mass concentrations in the combined set of *S. variegatus* sporocarps, (a) 137Cs/133Cs:K;

0 5 10 15 20 25

133Cs, mg kg-1

(b) 137Cs/133Cs:Rb; and, (c) 137Cs/133Cs:133Cs. \*\*\* p=0.001

0.0

1.0

2.0

137Cs/133Cs

3.0

4.0

5.0

Fig. 2. Relationship between 137Cs and K, Rb and 133Cs concentrations in sporocarps in the combined set of all *S. variegatus* sporocarps (a-f). K:Rb (a); K:133Cs (b); K:137Cs (c); Rb:133Cs (d); Rb:137Cs (e); and, 133Cs:137Cs (f). \*\*\* p=0.001

> 0.2 0.3 0.4 0.5 0.6 0.7 0.8

> > 0

5

10

15

133Cs, mg kg-1

20

25

Rb, g kg-1

K: b 133Cs

Rb:133Cs d

133Cs: f 137Cs

K, g kg-1

y = -0.1x + 32.8; r = -0.066

y = 0.02x + 0.26; r = 0.746\*\*\*

y = 0.11x + 1.75; r = 0.605\*\*\*

0 50 100 150 200

137Cs, kBq kg-1

0 10 20 30

133Cs, mg kg-1

0 10 20 30

133Cs, mg kg-1

y = 36.7x + 17.4; r = 0.505\*\*\*

y = 0.03x + 30.10; r = 0.103

y = 0.002x + 0.287; r = 0.440\*\*\*

0 50 100 150 200

137Cs, kBq kg-1

0 50 100 150 200

137Cs, kBq kg-1

0.2 0.4 0.6 0.8

Rb g kg-1

0.2 0.3 0.4 0.5 0.6 0.7 0.8

Rb, g kg-1

K, g kg-1

a K:Rb

K:137Cs c

Rb: e 137Cs

K, g kg-1

Fig. 2. Relationship between 137Cs and K, Rb and 133Cs concentrations in sporocarps in the combined set of all *S. variegatus* sporocarps (a-f). K:Rb (a); K:133Cs (b); K:137Cs (c); Rb:133Cs

(d); Rb:137Cs (e); and, 133Cs:137Cs (f). \*\*\* p=0.001

Fig. 3. Relationship between the 137Cs/133Cs isotopic (atom) ratios (x10−7) and K, Rb and 133Cs mass concentrations in the combined set of *S. variegatus* sporocarps, (a) 137Cs/133Cs:K; (b) 137Cs/133Cs:Rb; and, (c) 137Cs/133Cs:133Cs. \*\*\* p=0.001

Cesium (137Cs and 133Cs), Potassium

and Rubidium in Macromycete Fungi and *Sphagnum* Plants 295

The relation between 137Cs and K, and Rb and 133Cs within S*. variegatus* (Figure 2) was similar to an earlier report on different species of fungi (Yoshida & Muramatsu, 1998). Rubidium concentration in sporocarps was positively correlated with 133Cs and 137Cs, but generally negatively correlated with 137Cs/133Cs isotopic ratio, i.e. a narrower 137Cs/133Cs ratio in sporocarps resulted in higher Rb uptake by fungi. This ratio may reflect the soil layers explored by the mycelia (Rühm et al., 1997), as fungi have a higher affinity for Rb than for K and cesium (Ban-Nai et al., 2005; Yoshida & Muramatsu, 1998), and Rb concentrations in sporocarps can be more than one order of magnitude greater than in mycelium extracted as fungal sporocarps from soil of the same plots (Vinichuk et al., 2011). Soil mycelia always consist of numerous fungal species and the intraspecific relationships between soil mycelia and sporocarps has not yet been estimated; however, the development of molecular methods with the ability to mass sequence environmental samples in

combination with quantitative PCR may now enable such analysis to be conducted.

Japan over three years (Yoshida & Muramatsu, 1998).

time (Dahlberg et al., 1997).

even if large set of samples were analyzed.

Mass concentration of 133Cs and activity concentration of 137Cs have different relations in fungal sporocarps: in three of four genotypes, there was a high correlation, two of which were significant (r=0.908\*\* and r=979\*), and there was no correlation in the fourth genotype (r=−0.263, Table 7), whereas, correlation between 137Cs and 133Cs within the whole population was only moderate (r=0.605\*\*\* Figure 2). In terms of 133Cs and 137Cs behavior, there would be no biochemical differentiation, but there could be differences in atom abundance and isotopic disequilibrium within the system. Fungi have large spatiotemporal variation in 133Cs and 137Cs content in sporocarps of the same species and different species (de Meijer et al., 1988), and the variation in K, Rb, 133Cs and 137Cs concentrations within a single genotype appeared similar, or lower, than the variation within all genotypes. The results for 137Cs and alkali elements in a set of samples of *S. variegatus,* collected during the same season and consisting of sporocarps from both different and the same genotype, indicated the variability in concentrations was similar to different fungal species collected in

The relatively narrow range in K and Rb variation and the higher 133Cs and 137Cs variations might be due to different mechanisms being involved. The differences in correlation coefficients between 137Cs and the alkali metals varied among and within the genotypes of *S. variegatus*, suggesting both interspecific and intrapopulation variation in the uptake of K, Rb, stable 133Cs and, 137Cs and, their relationships could be explained by factors other than genotype identity. The variability in 137Cs transfer depends on the sampling location of fungal sporocarps (Gillett & Crout, 2000), for *S. variegatus,* these interaction factors might include the spatial pattern of soil chemical parameters, heterogeneity of 137Cs fallout, mycelia location, and heterogeneity due to abiotic and biotic interactions increasing over

Within the combined set of sporocarps the concentration of Rb and 137Cs activity concentration in *S. variegatus* sporocarps were normally distributed but the frequency distribution of 133Cs and K was not: asymmetry of 137Cs frequency distributions is reported in other fungal species (Baeza et al., 2004; Gaso et al., 1998; Ismail, 1994). According to Gillett & Crout (2000), the frequency distribution of 137Cs appears species dependent: high accumulating species tend to be normally distributed and low accumulating species tend to be log-normally distributed. However, lognormal distribution is almost the default for concentration of radionuclides and is unlikely to be a species-specific phenomenon, as it also occurs in soil concentrations, which implies normal distribution would not be expected,


1\* p=0.05; \*\* p=0.01; \*\*\* p=0.001

Table 7. Correlation coefficients between concentrations of potassium, rubidium and cesium (133Cs and 137Cs) in genotypes of *S. variegatus* with more than four sporocarps analyzed1.

The concentration of K in sporocarps appeared independent of the 137Cs/133Cs isotopic ratio in both the whole population (Figure 3) and among the genotypes, with one exception (Table 7). The absence of correlation between 137C (or 133Cs) and K in fungi may be due to the incorporation of K being self-regulated by the nutritional requirements of the fungus, whereas, incorporation of 137Cs is not self-regulated by the fungus (Baeza et al., 2004). Although K and cesium (133Cs and 137Cs) concentrations did not correlate within *S. variegatus*, both K+ and Cs+ ions may compete for uptake by fungi. In experiments under controlled conditions and with sterile medium (Bystrzejewska-Piotrowska & Bazala, 2008), the competition between Cs+ and K+ depends on Cs+ concentration in the growth medium and on the path of Cs+ uptake. In studies of Cs uptake by hyphae of basidiomycete *Hebeloma vinosophyllum* when grown on a simulated medium (Ban-Nai et al., 2005), the addition of monovalent cations of K+, Rb+, and NH4 + reduced uptake of Cs. In addition, radiocesium transport by arbuscular mycorrhizal (AM) fungi decreases if K concentration increases in a compartment accessible only to AM (Gyuricza et al., 2010), and a higher Cs:K ratio in the nutrient solution increases uptake of Cs by ectomycorrhizal seedlings (Brunner et al., 1996). A noticeable (20-60%) and long-lasting (at least 17 years) reduction in 133Cs activity concentration in fungal sporocarps *in situ* due to a single K fertilization of 100 kg ha−1 in a Scots pine forest is reported by Rosén et al., (2011).

Genotype 2-1 (8 sporocarps) K 0.502

Genotype 2-2 (6 sporocarps) K −0.472

Genotype 4-3 (4 sporocarps) K −0.531

Genotype 7-7(5 sporocarps) K −0.562

1\* p=0.05; \*\* p=0.01; \*\*\* p=0.001

Rb 0.626\* 0.966\*\*\*

Rb −0.658 0.928\*\*

Rb 0.177 0.696

Rb −0.472 0.987\*\*

monovalent cations of K+, Rb+, and NH4

Scots pine forest is reported by Rosén et al., (2011).

133Cs 0.908\*\* 0.745\* 0.837\*\*

133Cs −0.263 −0.138 0.159

133Cs 0.979\* −0.569 0.182

133Cs 0.699 −0.528 −0.404

137Cs/133Cs −0.172 −0.058 0.240

137Cs/133Cs −0.352 −0.608 −0.586

137Cs/133Cs −0.488 0.163 0.930

137Cs/133Cs −0.115 −0.155 −0.345

Table 7. Correlation coefficients between concentrations of potassium, rubidium and cesium (133Cs and 137Cs) in genotypes of *S. variegatus* with more than four sporocarps analyzed1.

The concentration of K in sporocarps appeared independent of the 137Cs/133Cs isotopic ratio in both the whole population (Figure 3) and among the genotypes, with one exception (Table 7). The absence of correlation between 137C (or 133Cs) and K in fungi may be due to the incorporation of K being self-regulated by the nutritional requirements of the fungus, whereas, incorporation of 137Cs is not self-regulated by the fungus (Baeza et al., 2004). Although K and cesium (133Cs and 137Cs) concentrations did not correlate within *S. variegatus*, both K+ and Cs+ ions may compete for uptake by fungi. In experiments under controlled conditions and with sterile medium (Bystrzejewska-Piotrowska & Bazala, 2008), the competition between Cs+ and K+ depends on Cs+ concentration in the growth medium and on the path of Cs+ uptake. In studies of Cs uptake by hyphae of basidiomycete *Hebeloma vinosophyllum* when grown on a simulated medium (Ban-Nai et al., 2005), the addition of

transport by arbuscular mycorrhizal (AM) fungi decreases if K concentration increases in a compartment accessible only to AM (Gyuricza et al., 2010), and a higher Cs:K ratio in the nutrient solution increases uptake of Cs by ectomycorrhizal seedlings (Brunner et al., 1996). A noticeable (20-60%) and long-lasting (at least 17 years) reduction in 133Cs activity concentration in fungal sporocarps *in situ* due to a single K fertilization of 100 kg ha−1 in a

+ reduced uptake of Cs. In addition, radiocesium

137Cs K Rb 133Cs

The relation between 137Cs and K, and Rb and 133Cs within S*. variegatus* (Figure 2) was similar to an earlier report on different species of fungi (Yoshida & Muramatsu, 1998). Rubidium concentration in sporocarps was positively correlated with 133Cs and 137Cs, but generally negatively correlated with 137Cs/133Cs isotopic ratio, i.e. a narrower 137Cs/133Cs ratio in sporocarps resulted in higher Rb uptake by fungi. This ratio may reflect the soil layers explored by the mycelia (Rühm et al., 1997), as fungi have a higher affinity for Rb than for K and cesium (Ban-Nai et al., 2005; Yoshida & Muramatsu, 1998), and Rb concentrations in sporocarps can be more than one order of magnitude greater than in mycelium extracted as fungal sporocarps from soil of the same plots (Vinichuk et al., 2011). Soil mycelia always consist of numerous fungal species and the intraspecific relationships between soil mycelia and sporocarps has not yet been estimated; however, the development of molecular methods with the ability to mass sequence environmental samples in combination with quantitative PCR may now enable such analysis to be conducted.

Mass concentration of 133Cs and activity concentration of 137Cs have different relations in fungal sporocarps: in three of four genotypes, there was a high correlation, two of which were significant (r=0.908\*\* and r=979\*), and there was no correlation in the fourth genotype (r=−0.263, Table 7), whereas, correlation between 137Cs and 133Cs within the whole population was only moderate (r=0.605\*\*\* Figure 2). In terms of 133Cs and 137Cs behavior, there would be no biochemical differentiation, but there could be differences in atom abundance and isotopic disequilibrium within the system. Fungi have large spatiotemporal variation in 133Cs and 137Cs content in sporocarps of the same species and different species (de Meijer et al., 1988), and the variation in K, Rb, 133Cs and 137Cs concentrations within a single genotype appeared similar, or lower, than the variation within all genotypes. The results for 137Cs and alkali elements in a set of samples of *S. variegatus,* collected during the same season and consisting of sporocarps from both different and the same genotype, indicated the variability in concentrations was similar to different fungal species collected in Japan over three years (Yoshida & Muramatsu, 1998).

The relatively narrow range in K and Rb variation and the higher 133Cs and 137Cs variations might be due to different mechanisms being involved. The differences in correlation coefficients between 137Cs and the alkali metals varied among and within the genotypes of *S. variegatus*, suggesting both interspecific and intrapopulation variation in the uptake of K, Rb, stable 133Cs and, 137Cs and, their relationships could be explained by factors other than genotype identity. The variability in 137Cs transfer depends on the sampling location of fungal sporocarps (Gillett & Crout, 2000), for *S. variegatus,* these interaction factors might include the spatial pattern of soil chemical parameters, heterogeneity of 137Cs fallout, mycelia location, and heterogeneity due to abiotic and biotic interactions increasing over time (Dahlberg et al., 1997).

Within the combined set of sporocarps the concentration of Rb and 137Cs activity concentration in *S. variegatus* sporocarps were normally distributed but the frequency distribution of 133Cs and K was not: asymmetry of 137Cs frequency distributions is reported in other fungal species (Baeza et al., 2004; Gaso et al., 1998; Ismail, 1994). According to Gillett & Crout (2000), the frequency distribution of 137Cs appears species dependent: high accumulating species tend to be normally distributed and low accumulating species tend to be log-normally distributed. However, lognormal distribution is almost the default for concentration of radionuclides and is unlikely to be a species-specific phenomenon, as it also occurs in soil concentrations, which implies normal distribution would not be expected, even if large set of samples were analyzed.

Cesium (137Cs and 133Cs), Potassium

mosses in particular are found (Bunzl & Kracke, 1989).

moss compartments (Dragović et al., 2004).

unclear.

processes in peatlands.

and Rubidium in Macromycete Fungi and *Sphagnum* Plants 297

poor ecosystem often formed and dominated by peat mosses (*Sphagnum*). *Sphagnum*dominated peatlands with some groundwater inflow (i.e. weakly minerotrophic 'poor fens') are almost as nutrient poor and acid as true bogs. *Sphagnum* plants absorb and retain substantial amounts of fallout-derived radiocesium, and some attention has been given to the transfer of the radioactive cesium isotope 137Cs within raised bogs (Bunzl & Kracke, 1989; Rosén et al., 2009), and relatively high 137Cs bioavailability to bog vegetation and

The transfer of 137Cs within a peatland ecosystem is different from that in forest or on agricultural land. In soils with high clay content, there is low bioavailability and low vertical migration rate of radiocesium due to binding to some clay minerals (Cornell, 1993). In nutrientpoor but organic-matter-rich forest soils, the vertical migration rate of 137Cs is also low, but bioavailability is often high, particularly for mycorrhizal fungi (Olsen et al., 1990; Vinichuk & Johansson, 2003; Vinichuk et al., 2004; 2005). In forests and pastures, extensive fungal mycelium counteracts the downward transport of 137Cs by an upward translocation flux (Rafferty et al.,

In peatlands, 137Cs appears to move through advection in peat water (review by Turetsky et al., 2004). Small amounts of clay mineral in the peat reduce Cs mobility (MacKenzie et al., 1997), but most *Sphagnum* peat is virtually clay mineral free organic matter. In wet parts of open peatlands that lack fungal mycelium, the downward migration of 137Cs in the *Sphagnum* layers is expected to be faster than in forest soil and Cs is continuously translocated towards the growing apex of the *Sphagnum* shoots, where it is accumulated. Some attempts have been made to investigate whether 137C is associated with essential biomacromolecules in mosses and to determine the 137Cs distribution among intracellular

The chemical behavior of radiocesium is expected to be similar to that of stable 133Cs and other alkali metals, i.e. K, Rb, which have similar physicochemical properties. Moreover, stable 133Cs usually provides a useful analogy for observing long-term variation and transfer parameters of 137Cs in a specific environment, particularly in peatlands that are cut off from an input of stable Cs from the mineral soil. As the relationship between K and Rb in fungi is not clearly understood, whether Cs follows the same pathways as K in *Sphagnum* is also

Thus, the 137Cs activity concentration and mass concentration of K, Rb and 133Cs was analyzed within individual *Sphagnum* plants (down to 20 cm depth) growing on a peatland in eastern central Sweden and its distribution in the uppermost capitulum and subapical segments of *Sphagnum* mosses were compared to determine the possible mechanisms

Additionally, the isotopic (atom) ratios of 137Cs/K, 137Cs/Rb and 137Cs/133Cs within individual *Sphagnum* plants were recorded for determining the distribution of 137Cs and alkali metal, and to obtain a better understanding of the uptake mechanisms and the biological behavior of 137Cs in nutrient-poor *Sphagnum* dominated ecosystem. There are few studies on the influence of alkali metals (K, Rb, 133Cs) on 137Cs distribution and cycling

Plant species growing on peat have varying degree capacities for influencing uptake and binding of radionuclides, but no systematic study has covered all the dominant species of *Sphagnum* peatlands their competition for radionuclides and nutrients. The important role of *Sphagnum* mosses in mineral nutrient turnover in nutrient-poor ecosystems, in particular

involved in radiocesium uptake and retention within *Sphagnum* plants.

2000); this results in a slow net downward transport of 137Cs in the soil profile.

## **1.8 Mechanisms of 137Cs and alkali metal uptake by fungi**

Generally, little is known about the mechanisms involved in the uptake and retention of radionuclides by fungi. Studies of uptake mechanisms and affinity for alkali metals in fungi are scarce, but some results are reviewed by Rodríguez-Navarro (2000). Compared to plants, fungal fruit bodies can be characterized by high 137Cs, 133Cs and Rb concentrations and low calcium (Ca) and strontium (Sr) concentrations. In a laboratory experiment with the woodinhabiting mushroom *Pleurotus ostreatus* (Fr.) Kummer Y-l (Terada et al., 1998), 137Cs uptake by mycelia decreased with increasing of 133Cs, K or Rb concentration in the media, and K uptake by mycelia decreased with increasing of 133Cs concentration. In an experiment with pure cultures of mycorrhizal fungi (Olsen et al., 1990) some species had preference for Cs over K and in the experiments with yeast (Conway & Duggan, 1958), K had preference over Cs and the affinity for alkali metal uptake decreased in the order K+ < Rb+ < Cs+ followed by Na+ and Li+, with a relative ratio of 100:42:7:4:0.5. Fungi (mycelium and sporocarps) have a higher affinity for uptake of Rb and K to Cs, and based on the CR values for fungal sporocarps (Table 3), alkali metal can be ranked in the order Rb+ > K+ > Cs+, with a relative ratio of 100:57:32, which is within the range of 100:88:50 derived by Yoshida & Muramatsu (1998).

The affinity for an alkali metal depends on the nutritional status of the organism, which at least partly explains differences reported between field experiments and laboratory experiments with a good nutrient supply. The mycorrhizal species *Sarcodon imbricatus* was found to be the most efficient in accumulating K, Rb and Cs, which was in agreement with results obtained by Tyler (1982), where a mean CR for Rb in litter decomposing fungus *Collybia peronata* was reported to be 41, and the mean CR for Rb in *Amanita rubescens*, which is mycorrhizal with several tree species, was above 100. However, lower 40K content for mycorrhizal species is reported by Römmelt et al. (1990), which means mycorrhizal species do not necessarily accumulate alkali metals more efficiently than saprotrophic ones.

Accumulation of stable and radioactive cesium by fungi is apparently species-dependent but is affected by local environmental conditions. According to de Meijer et al. (1988), the variation in concentrations of stable and radioactive cesium in fungi of the same species is generally larger than the variation between different species and the variation in 137Cs levels within the same genet of *S. varegatus* is as large as within non-genet populations of the species (Dahlberg et al., 1997), suggesting both interspecific and intrapopulation variation in the uptake of K, Rb, stable 133Cs and 137Cs, and that their relationships can be explained by factors other than genotype identity (Vinichuk et al., 2011). There is about two orders of magnitude variation in Cs uptake, with the highest CR value in e.g. *S. imbricatus* (256) and the lowest in *Lactarius deterrimus* (2.6), although other studies (Seeger & Schweinshaut, 1981) report the highest accumulation of stable Cs is in *Cortinarius* sp.
