158 in AT0000037

158 in AT0000037 RADIOCAESIUM DISTRIBUTION IN FRUTTBODIES AND MYCORRHIZAE OF FUNGI IN SWEDISH FORESTS lLNikoIova> 2K.J.Johanson,3 A.Dahlberg ^.Poushkarov Institute of Soil Science & Agroecology, PO Box 1369 1080 Sofia, Bulgaria, department of Radioecology, SLU, PO Box 7031 Uppsala, Sweden, ^Department of Forest Mycology & Pathology, SLU, PO Box 7026, Uppsala, Sweden Introduction In Sweden, transfer of *•?' Cs from the forest ecosystems to man seems to be a major part of the total ^Cs transfer to man. There are three important pathways: by berries, by game animals and by mushrooms. In mushrooms the ^^Cs activity concentration vary between different species with at least one order of magnitude. There has been a suggestion that a large fraction of the 137 cs in the forest soils might be bound in fungal mycelium. Materials and methods The study area was a coniferous forest, located about 40 km Northwest of Uppsala. The 137Cs ground deposition is between 30.000 and 40.000 Bq m^. Samples of fruitbodies of some fungal species were collected and at the laboratory divided into cap and stipe and measured separately. Samples of fruitbodies of Suillus variegatus and Lactarius rufus and corresponding samples of mycorrhizae assumed to be S.variegatus and L. rufus were collected within a few m~2, mainly on rocky area. The fruitbodies were cut into pieces and transferred as fresh material into plastic vials for determination of the activity using Ge-detectors. The mycorrhizae were dissected from the soil and the activity was determined in NaI(Tl) detector. The samples were dried at 55 C, weighed after measurements and the ^Cs, was expressed per dry weight (Bq kg"*). The verification of species identity was performed using RFLP analysis of the PCR-amplified r-DNA ITS-region. At specific sites where fruitbodies of Suillus variegatus were collected the soil depth to bed rock was measured. This article is an extended summary of a paper, which will be submitted to the J Environm. Radioactivity 159 Results and discussion Apart from a few fruitbodies, there were always higher levels of ^7QS activity concentration in the cap compared with the stipe (Table 1). In Cortinarius armillatus, the mean values for 2 sets of samples with 6 fruitbodies each were 130 and 113 kBq kg"1 d.w. in the caps and 50 and 43 in the stipe given a ratio of cap/stipe of 2.7. The transfer factor (TFg) for the cap of C. armijlatus was 3.5 rrfi kg"* and the corresponding TFg for the stipe was 1.4. The ^Cs activity concentration for Cortinarius subtortus were 347 kBq kg'1 for the caps and 223 for the stipe, with a ratio of 1.6. The TFg for the cap of C. subtortus was very high, or 9.3 m^ kg"1. The corresponding value for the stipe was 6.0. The stipe/cap ratios for Cortinarius mucosus and for Russula integra were 3.0 and 2.0, respectively. Table 1 The distribution of 137Cs activities (kBq kg"1 dw) and the transfer factor (TFg, Bq kg'1 dw/ Bq m"2) in stipes and caps of fruitbodies of Cortinarius armillatus, C. subtortus, C. mucosus and Russula integra. Stipe TFg Cap TFg Ratio C. armiUatus, n=6 50±16 1.4 130±28 3.5 2.7 C. armillatus, n=6 43±13 1.2 113±42 3.1 2.7 C. subtortus, n=6 223±46 6.0 347±48 9.3 1.6 C. mucosus, n=4 30±20 0.8 69±19 1.9 3.0 R. integra, n=4 40±24 1.1 71±27 1.9 2.0 The result of the RFLP analysis showed that the mycorrhizae suspected to be S. variegatus were found to be S .variegatusin contrast, the mycorrhizae suspected to be L rufus were in most cases other species, mainly Russula species. The mean 137cs activity concentration in fruitbodies of S. variegatus was 98 kBq kg"1 and 35 kBq kg"1 in mycorrhizae.Since about 50% of mycorrhizae is fungi and the rest is the roots of the vascular plant part in the symbiosis, there seem to be only minor differences in the i^Cs levels in fruitbodies and mycelium. The TFg for this set of S. variegatus was 2.6 xrP- kg"1 for fruitbodies and 0.9 for mycorrhizae. The corresponding values for "L. rufus" were 1.5 for fruitbodies and 1.2 for mycorrhizae. 160 Table 2. The l^Cs activity concentrations in fruitbodies and mycorrhizae of Suillus variegatus and in fruitbodies of Lactarius rufus. with corresponding mycorrhizae (Lactarius spp.and Russula spp.) and the ratio fruitbodies/ mycorrhizae. Fruitbodies TFg Mycorrhizae TFg Ratio kBq kg"1 dw kBqkg-idw Suillus variegatus before production of 68±33 fruitbodies. N =7. during production of 98±51 2.6 35±32 0.9 0.36 fruitbodies. N = 7. "Lactarius rufus" before production of 12±9 fruitbodies. N = 20. during production of 57±27 1.5 44±14 1.2 0.77 fruitbodies. N = 11. A poor correlation (r2 = 0.18) between 137Cs activity concentrations in fruitbodies and soil depth at the fruitbody site was found. The rather low r2 may at least partly be due to unknown soil parameters since the samples were harvested over an area of about 1 km2. A possible explanation for this correlation might be that with the same -^^Cs ground deposition in the more shallow soil layers higher ^"^Cs activity concentration was found compared to sites with thicker soil layers.(Fig. 1) Figure 1: Correlation between 137cs-activity concentrations in fruitbodies and soil depth at the fruitbody site 140 120 -- 100 -- St 80 u en 60 -• 40 -- 20 -• 0 i i I i i 0 10 12 Depth(cm).

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