Correlations between potassium, rubidium and cesium ( 133 Cs and 137 Cs) in sporocarps of Suillus variegatus in a Swedish boreal forest M. Vinichuk a, c, * , K. Rosén a , K.J. Johanson a , A. Dahlberg b a Department of Soil and Environment, Swedish University of Agricultural Sciences, P.O. Box 7014, SE-750 07 Uppsala, Sweden b Department of Forest Mycology and Pathology, Swedish University of Agricultural Sciences, P.O. Box 7026, 750 07 Uppsala, Sweden c Department of Ecology, Zhytomyr State Technological University, 103 Cherniakhovsky Str., 10005 Zhytomyr, Ukraine article info Article history: Received 28 October 2010 Received in revised form 1 February 2011 Accepted 13 February 2011 Available online 8 March 2011 Keywords: Ectomycorrhizal fungi K Rb 133 Cs 137 Cs abstract An analysis of sporocarps of ectomycorrhizal fungi Suillus variegatus assessed whether cesium ( 133 Cs and 137 Cs) uptake was correlated with potassium (K) or rubidium (Rb) uptake. The question was whether intraspecific correlations of Rb, K and 133 Cs mass concentrations with 137 Cs activity concentrations in sporocarps were higher within, rather than among, different fungal species, and if genotypic origin of sporocarps within a population affected uptake and correlation. Sporocarps (n ¼ 51) from a Swedish forest population affected by the fallout after the Chernobyl accident were studied. The concentrations were 31.9  6.79 g kg 1 for K (mean  SD, dwt), 0.40  0.09 g kg 1 for Rb, 8.7  4.36 mg kg 1 for 133 Cs and 63.7  24.2 kBq kg 1 for 137 Cs. The mass concentrations of 133 Cs correlated with 137 Cs activity concentrations (r ¼ 0.61). There was correlation between both 133 Cs concentrations (r ¼ 0.75) and 137 Cs activity concentrations (r ¼ 0.44) and Rb, but the 137 Cs/ 133 Cs isotopic ratio negatively correlated with Rb concentration. Concentrations of K and Rb were weakly correlated (r ¼ 0.51). The 133 Cs mass concen- trations, 137 Cs activity concentrations and 137 Cs/ 133 Cs isotopic ratios did not correlate with K concen- trations. No differences between, within or, among genotypes in S. variegatus were found. This suggested the relationships between K, Rb, 133 Cs and 137 Cs in sporocarps of S. variegatus is similar to other fungal species. Ó 2011 Elsevier Ltd. All rights reserved. 1. Introduction Radiocesium released after the Chernobyl accident in 1986 is still a critical fission product in the environment in Sweden because of its long half-life of 30 years. The behavior of 137 Cs in forest ecosystems differs substantially from other ecosystems, foremost due to the abundance of fungi, which contribute to the persistence of Chernobyl radiocesium in the upper horizons of forest soils (Vinichuk and Johanson, 2003). Saprotrophic and mycorrhizal fungi have key roles in nutrient and carbon cycling processes in forest soils (Dighton, 2003). Although fungal biomass is relatively low (Dighton et al., 1991; Rafferty et al., 1997), many fungal species accumulate more 137 Cs than vascular plants do (Rosén et al., 2009; Vinichuk et al., 2010b); hence, the contribution of fungi to 137 Cs cycling in forest systems is substantial. Fungal sporocarps may only account for about 0.5% (McGee et al., 2000), sometimes 0.01e0.1% (Nikolova et al., 1997), of the total radio- cesium within a forest ecosystem; however, due to the high levels of 137 Cs in sporocarps, their contribution to the internal dose in man may be high through consumption of edible mushrooms (Skuterud et al., 1997; Kalac ˇ , 2001). Fungi are important for 137 Cs uptake and migration in forest systems and since the Chernobyl accident, fungal species may contain high concentrations of radiocesium; however, the reasons and mechanisms for the magnitude higher concentration of radi- ocesium in fungi than in plants is unclear (Yoshida and Muramatsu, 1998; Kuwahara et al.,1998; Bystrzejewska-Piotrowska and Bazala, 2008). Fungi accumulate rubidium (Rb) and stable cesium ( 133 Cs) effectively (Gaso et al., 2000), and concentrations of 137 Cs, 133 Cs and Rb in fungal sporocarps can be one order of magnitude higher than those in plants growing in the same forest (Vinichuk et al., 2010a). However, the chemical behavior of the alkali metals, K, Rb and 133 Cs, is expected to be similar to 137 Cs, due to similarities in their physicochemical properties (Enghag, 2000). The concentrations of K, Rb and 133 Cs have been analyzed in fungal sporocarps (Tyler, 1980; Horyna and  Zanda, 1988; Yoshida * Corresponding author. Department of Soil and Environment, Swedish Univer- sity of Agricultural Sciences, P.O. Box 7014, SE-750 07 Uppsala, Sweden. Tel.: þ46 18 67 14 42; fax: þ46 18 67 28 95. E-mail addresses: Mykhailo.Vinichuk@slu.se, mykhailo59@gmail.com (M. Vinichuk). Contents lists available at ScienceDirect Journal of Environmental Radioactivity journal homepage: www.elsevier.com/locate/jenvrad 0265-931X/$ e see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.jenvrad.2011.02.007 Journal of Environmental Radioactivity 102 (2011) 386e392