Ideas and perspectives: truffles not radioactive

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Abstract
Although ranging among the most expensive gourmet foods, it remains unclear if Burgundy truffles (Tuber aestivum) accumulate radioactivity at a harmful level comparable to other fungi.Here, we measure the 137 Cs in 82 T. aestivum fruitbodies from Switzerland, Germany, France, Italy and Hungary.All specimens reveal insignificant radiocaesium concentrations, thus providing an all clear for truffle hunters and cultivators in Europe as well as dealers and customers from around the world.Our results are particularly relevant in the light of recent cultivation efforts and the fact that forest ecosystems are still highly contaminated with 137 Cs, for which mushrooms are the main pathways to human diets.

Study
Extensive cultivation efforts of the Burgundy truffle (Tuber aestivum Vittad.)far beyond its traditional homeland in France aim at supplementing wildlife harvests for the growing demand of a globalized market (Hall et al., 2003).Despite the rapidly increasing economic interest in this ectomycorrhizal ascomycete, most of the hypogeous life cycle is, however, not yet understood (Stobbe et al., 2012(Stobbe et al., , 2013)).Together, with a general lack of ecological insight, it remains unclear if truffles are accumulating radioactivity at a harmful level comparable to other fungal species and subsequent components of the trophic food web (Dighton et al., 2008;Hohmann and Huckschlag, 2005;Strebl and Tataruch, 2007;Steiner and Fielitz, 2009;Mietelski et al., 2010).
Since the Chernobyl accident in 1986, large parts of Europe's topsoil are radioactively contaminated (De Cort et al., 1998;Evangeliou et al., 2013), with high radionuclide levels still implying concerns for ecotoxicology and human health.Some ectomycorrhizal and saprotrophic fungi appear particularly prone to mediating and incorporating radiocaesium 137 ( 137 Cs) (Dighton et al., 2008), with different melanin contents and mycelium depths contributing to species-specific rates of radio-resistance and 137 Cs Introduction

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Full accumulation (Mietelski et al., 2010).In regions where aerosol fallout after Chernobyl was most intense, not only mushrooms but also later components in the food chain, including game meat of red deer, roe deer and wild boar, still exceed the 137 Cs tolerance value of 600 Bq kg −1 (Hohmann and Huckschlag, 2005;Strebl and Tataruch, 2007;Steiner and Fielitz, 2009).
Here, we measure 137 Cs activity concentrations of 82 T. aestivum, harvested by trained dogs between 2010 and 2014 in natural habitats and plantations across Switzerland, Germany, France, Italy and Hungary (Fig. 1a).Individual fruitbodies were cleaned and grinded for γ-spectrometry.After correction for the decay rate, all specimens reveal insignificant 137 Cs values below the detection limit of 2 Bq kg −1 (determined by the background noise, counting efficiency, processing time and sample weight).This result suggests an all clear for Burgundy truffle hunters and cultivators in Europe as well as dealers and customers all over the world.Our findings, in agreement with previous, local-scale evidence from Italy (Lorenzelli et al., 1996), are surprising as mycorrhizal mushrooms play a key role in the radioecology of natural ecosystems (Fig. 1b).Hypogeous deer truffles (Elaphomyces granulatus), for instance, range amongst the most contaminated fungi (Hohmann and Huckschlag, 2005;Strebl and Tataruch, 2007;Steiner and Fielitz, 2009).Reasons for non-radioactive T. aestivum possibly involve species-specific requirements for soil structure and chemistry, together with mycelium depth, melanin content and/or the lack of 137 Cs binding pigments.It has also been argued that calcium carbonate reduces the soil-plant transfer of 137 Cs, while its availability for plants is high in nutrient-poor organic soil horizons (Mascanzoni, 2001(Mascanzoni, , 2009)).
Truffles generally fruit near the surface of calcareous substrate (Stobbe et al., 2012(Stobbe et al., , 2014)).Nevertheless, more insight is needed into the chemical composition of truffle fruitbodies and their symbiotic interaction with host roots (Büntgen and Egli, 2014), considering potential effects on the cycling of ambient 137 Cs from both Chernobyl and atmospheric testing in the 1950s and 1960s.These, and associated tasks surrounding the hidden world of truffles appear timely in the light of recent cultivation efforts (Hall

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Full  et al., 2003;Stobbe et al., 2013), as well as the fact that forest ecosystems still provide ample 137 Cs for uptake with mushrooms representing the main pathway to human diets (Mascanzoni, 2009).Further relevance emerges from the environmental contamination of Fukushima and a higher transfer rate of radionuclides under global warming.Introduction

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Full Mass-specific mean 137 Cs detection limit (after ∼ 20 h) of truffle fruitbodies (∼ 45 g) classified after local deposition levels (numbers refer to the amount of samples per deposition level), together with published 137 Cs contamination values of edible and toxic (black dot) mycorrhizal and saprotrophic (white star) above-and belowground (white square) mushrooms (Dighton et al., 2008;Steiner and Fielitz, 2009;Mascanzoni, 2001), as well as game meat (Strebl and Tataruch, 2007).Horizontal lines are tolerance values for food (100 Bq kg −1 ) and fungi/game (600 Bq kg −1 ).
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