*5.2.2. Brazil nuts*

Many milk products were analysed in 1986: Swiss cheese, milk powder, butter, yogurt, and cream [34, 36]. These investigations showed the same trends in somewhat lower activity concentrations. Two drinks also showed higher levels of radiocaesium (22–96 Bq/L in 1987), as they contained milk serum. The same contaminated milk from 1986 was used to produce milk powder. This milk powder was used for the production of chocolates. Milk chocolate contains 20 to 25 g milk powder (160–200 mL milk) per 100 g chocolate. We analysed the first samples in autumn 1986 for a local chocolate producer. Soon, we noticed higher levels when chocolates contained hazelnuts. These chocolate samples were in the range of 55±13 Bq/kg radiocaesium. In contrast, chocolates without nut ingredients showed lower activities (12±3 Bq/kg). These investigations showed that the contamination level of chocolates is even more from the use of hazelnuts (60%) than from the milk (~40%). In the following year, we found even higher radiocaesium values: 710 Bq/kg in chocolates without hazelnuts and 1.3 kBq/kg in chocolates with hazelnuts. Even chocolates without hazelnuts showed higher values. We explained this with higher values in milk. Hence, we started a special survey programme for

**Figure 3. Activity concentrations of radiocaesium in hazelnuts.** Plots to the left: Comparison of the radiocaesium lev‐ el in chocolates with and without hazelnuts (1986). Plot to the right: Development of the activity in hazelnuts from

The investigation of chocolates containing hazelnuts showed that the latter were part of the contamination. In 1986 and 1987, more than 180 hazelnut samples from a chocolate producer of the region were analysed for radiocontaminants. In 1987, the contamination level reached a total radiocaesium activity of up to 17 kBq/kg. Most hazelnuts were imported from Turkey, a country that was seriously contaminated with fallout from Chernobyl. Since 1989, we also investigated different nuts from other countries. Hazelnuts from Turkey remained the only contaminated nut species. Even in 2007, 21 years after the catastrophe of Chernobyl, one hazelnut sample had to be rejected. It did not reach the limit value but was over the tolerance

hazelnuts.

140 Radiation Effects in Materials

Basel.

**5.2. Wild-grown vegetables**

*5.2.1. Hazelnuts and other nuts*

Brazil nuts (*Bertholletia excelsa*) are known to accumulate earth alkaline metals from soil. First, this was shown with barium. Then, Penna-Franca detected the radium nuclides 226Ra and 228Ra, both from the natural decay series of uranium and thorium, in amounts of 50 Bq/kg. In Switzerland, imported Brazil nuts showed 61 to 112 Bq/kg total radium. This means 1000-fold of the radium content of the total diet in Europe. The consummation of Brazil nuts is estimated to be 0.1 g/day and person. Therefore, the consummation of Brazil nuts is not relevant. In literature, it is advised to consume Brazil nuts to enhance the selenium level. Two Brazil nuts lead to a yearly dose of 160 μSv, which is relevant [8].

Another important alkaline earth metal is strontium. Its most important radioactive nuclide is 90Sr. Froidevaux et al. [37] measured 11 to 15 Bq/kg in imported Brazil nuts. As Brazil nuts are often part of nut mixtures, the measured natural radioactivity is mainly produced by the Brazil nuts contained in the mixture.

### *5.2.3. Mushrooms*

Mushrooms are known to be organisms that can accumulate heavy metals from soil. Therefore, mushrooms from abroad and from Switzerland were of concern in 1987. More than 200 samples were analysed in our laboratory for radiocaesium. 24 samples had to be rejected. They showed a contamination level of more than 600 Bq/kg. The range of all analysed mushrooms was from 107 to more than 8000 Bq/kg. Swiss mushrooms and mushrooms from abroad then did not show any significant difference in their contamination level [38]. From 1989 on, mushrooms were regularly analysed, but violations became rare.

A quite different situation could be observed in South Bavaria, Germany. At the end of April 1986, much Chernobyl fallout was washed out in southern Bavaria over several days. In Munich, the local dose rate increased up to 1.1 μSv/h (10-fold over the normal value). Therefore, the contamination level in wild-grown mushrooms and berries reached high values (five-fold the normal radiocaesium activities due to the bomb fallout). Mushrooms with mycorrhiza, such as boletus species (*Hydnum repandum* and *Boletus badius*), blueberries, mosses, and lichens, were most affected [39–41]. Other mushrooms, such as porcini, champignons, and chanterelles, did not show this effect. In 2002, bay boletes (*B*. *badius*) showed radiocaesium levels of 33 to 23,200 Bq/kg and porcini from 6 to 10,000 Bq/kg. In 2015, activities were reduced remarkably in boletes 13 to 900 Bq/kg and porcini 4 to 108 Bq/kg [39]. Similar values were reported in Austria [42] and Switzerland [43]. Even in 2015, bay boletes were found with maximum activities of more than 2600 Bq/kg, whereas porcini showed a reduced contamination level with a maximum of 416 Bq/kg. The reduction was slow compared to West European countries. For example, in Spain, values ranged from 1 to 122 Bq/kg for radiocaesium and from 0.2 to 3.5 Bq/kg for radiostrontium. Mushrooms of a special region in the canton of Aargau (Swit‐ zerland) show a continuous fall of the activity from 1986 to 2014 [44].

Wood soils build their own biosphere: dead leaves, pins, etc., build the humic fraction of the soil. The plants take up the radioactivity from the soil. The radioactivity is recycled to the soil through the fall of the leaves and pins.
