*5.12.2. Natural radionuclides*

food samples (**Table 2**). As can be noticed, the radiostrontium level of tea is approximately 5±7 Bq/kg and could be found in every tea sample analysed. This contamination mainly comes from the bomb's fallout. Teas from other countries of the Far East also contain radiostrontium

<0.5–87 <0.5–171 <0.5–258 <0.1–57

<0.5–0.7 <0.5–0.7

<0.2 0.31±0.04 (2) 0.31±0.04 (2) N/A <0.2–0.3 <0.2–0.3

<0.1 0.5±0.2 (1) 0.5±0.2 (1) N/A

<0.2 6.3±8.1 (2) 6.3±8.1 (2) N/A <0.2–12 <0.2–12

<0.2 0.3±0.2 (1) 0.3±0.2 (1) N/A <0.2–0.3 <0.2–0.3

<0.5–3.9 <0.5–9.8 <0.5–14

All values in Bq/kg. First line: mean ± standard deviation of the activity concentrations; the number of samples with values over the detection limit is bracketed. The total of analysed samples per food category is set in brackets after the

1981, when our laboratory started with the radioactivity survey of food, water, besides milk, was the first food category to be monitored. Before 1986, no bomb fallout was detectable in the drinking water of Basel (<0.01 Bq/L radiocaesium). Just after the accident at Chernobyl, radioiodine and radiocaesium were detectable in small amounts of 59±77 and 9±9 Bq/L in some drinking water reservoirs of the state of Jura. The production of drinking water of the city of

Divers (28) <0.2 0.52±0.54 (2) 0.52±0.54 (2) N/A

food category name. Second line: activity concentration range of all samples. N/A, not analysed.

**Table 2.** Overview of investigated food imports from Japan from 2011 to 2015.

3.9 (1) 5.0±6.9 (2) 6.9±9.6 (2) 0.5±0.4 (2)

<0.2–0.14 <0.2–0.14

<0.2–2.4 <0.2–2.4 <0.01–1.0

**Food category 134Cs 137Cs 134+137Cs 90Sr** Tea (157) 13.4±24.8 (30) 9.9±28.6 (86) 8.0±33 (90) 5.2±7.4 (94)

Soups, miso, (44) <0.5 0.34±0.24 (9) 0.34±0.24 (9) N/A

Algae (60) <0.2 0.6±0.7 (9) 0.6±0.7 (9) 0.56±0.31 (12)

[77, 78].

148 Radiation Effects in Materials

Rice and rice products (24)

Soja and soja products (7)

Cereals and cereal products (26)

(15)

Vegetables, fruits

**5.12. Mineral and tap waters**

*5.12.1. Artificial radionuclides*

Basel was never affected.

Fish and fish products (4)

After 1995, the focus was set on the natural radionuclides from the uranium and thorium decay series. First, uranium and radium were analysed in tap and mineral waters of Switzerland and of abroad. Uranium and radium were found in activity concentrations from <10 to 250 mBq/L and from <10 to 200 mBq/L, respectively. In 2005, the Federal Office of Health analysed more than 5,500 water samples for their uranium content [79]. The World Health Organisation (WHO) considers uranium as relevant in drinking water because of its toxicity as a heavy metal. The WHO recommends a limit value of 30 μg/L (376 mBq/L) for drinking water [80]. In Germany, the tap water from more than 500 drinking water plants were analysed for their natural radionuclides. According to this study, the drinking water of 10% of all plants was over the limit dose of 0.1 mSv/year [81]. One possible input of uranium is supposed to come from the use of phosphate fertilisers in agriculture. These fertilisers may contain uranium up to 50 mg U/kg P2O5, which was shown by a market survey in Basel [82]. Our investigation gave cause for a national investigation of the Federal Office of Agriculture. The uranium is relatively soluble and washed from the fertiliser into the soil. From there, it is transferred into ground‐ water. Surbeck [83] estimated that the use of fertilisers results in the increase of the uranium concentration in groundwater from <0.1 to 3 μg/kg. In 2014, we analysed the tap water of all villages of the states of Basel-Campaign and Basel-City. The spectrum of the relevant radio‐ nuclides was expanded with 222Rn and 210Po. For uranium and radium, we found 12±16 mBq/ L (n=120) and 17±27 mBq/L (n=54). Radon was present in all samples in the Becquerel range (5±6 Bq/L). Also, 210Po was present in 57 samples in the low mBq range of 26±30 mBq/L [84]. In the alpine regions of southern Switzerland, the activity concentrations were somewhat higher due to the geological underground [85].
