**5. Results from 35 years of food control**

In Basel, the Government decided to buy the equipment for the monitoring of β- and γ-nuclides in 1980 because of the NPP accident at Harrisburg in 1979. Therefore, we were the only state laboratory that was prepared when the accident at Chernobyl happened. In 1986 and 1987, thousands of samples were analysed.

The fallout from bomb tests and the NPP accident of Chernobyl resulted in the ubiquitous contamination of the landscapes of the Northern Hemisphere. The core meltings at the NPP of Fukushima-Daiji also reached Europe, but the fallout was considerably lower than from Chernobyl. The situation after the Chernobyl fallout in Switzerland is well described in some papers [31–33, 98].

The contamination of farmland leads to contaminated food, such as milk or vegetables. These matrices are an important part of the Swiss survey programme. The fallout from Chernobyl affected the regions of southern Switzerland the most (total rain of 350 mm). This has to be compared to the washout in eastern Switzerland with 150 mm and the regions of Basel and Jura with 50 mm rain.

## **5.1. Milk and milk products**

In 1981, the State Laboratory Basel-City started the first regular radioanalyses in Basel. Milk samples from local milk production centres in northwest Switzerland of the states (cantons) of Aargau, Basel-Campaign, Basel-City, Solothurn, and Jura were analysed with β- and γspectrometry. On 2 May 1986, after the accident in Chernobyl, the frequency of the survey was intensified. On 4 and 5 May, radioiodine activity concentrations between 220 and 650 Bq/L 131I were measured. The milk from the mountainous region of the state of Jura showed lower values than in the states localised in the plain: 178 Bq/L 131I (4 May). In the milk distribution centres of Basel-City, the milk from the different regions had to be mixed in such a way that the population received milk with activities below 350 Bq/L. Due to its short half-life, the activity of radioiodine fell under the detection limit (0.1 Bq/L) in July. The activities of caesium and strontium were quite lower but resisted longer. The activity line of total caesium in the milk of the state of Jura (**Figure 2**) shows a maximum value of 127 Bq/L. In the following 3 years, smaller peak values could be observed due to the fact that the cows were fed with contaminated hay from the year before. After 1990, the total caesium level fell below 1 Bq/L, except for some farms in southern Switzerland, where, even in 2013, the radiocaesium level of the milk of one farm was over the tolerance limit of 10 Bq/kg.

The samples (1–5 g material) are inserted into the core over a cannula through the so-called glory hole and irradiated for 30 min with a power rate of 2 kW. After a cooling time of some

We used INAA for the analysis of total bromine content. Bromide is built by the decay of the fumigant methyl bromide. We used this technique for many years to determine the total bromine in spices, tea, and dried mushrooms. Another application is the determination of the total bromine content as a screening analysis for flame-retardants in plastic materials [29]. 238U and 232Th can be determined by INAA in suspended matter and sediments [30]. In addition, total iodine content in iodine rich food, such as algae, can be determined over the activation

We mentioned the use of INAA as a completion of the possibilities of γ-spectrometry. These

In Basel, the Government decided to buy the equipment for the monitoring of β- and γ-nuclides in 1980 because of the NPP accident at Harrisburg in 1979. Therefore, we were the only state laboratory that was prepared when the accident at Chernobyl happened. In 1986 and 1987,

The fallout from bomb tests and the NPP accident of Chernobyl resulted in the ubiquitous contamination of the landscapes of the Northern Hemisphere. The core meltings at the NPP of Fukushima-Daiji also reached Europe, but the fallout was considerably lower than from Chernobyl. The situation after the Chernobyl fallout in Switzerland is well described in some

The contamination of farmland leads to contaminated food, such as milk or vegetables. These matrices are an important part of the Swiss survey programme. The fallout from Chernobyl affected the regions of southern Switzerland the most (total rain of 350 mm). This has to be compared to the washout in eastern Switzerland with 150 mm and the regions of Basel and

In 1981, the State Laboratory Basel-City started the first regular radioanalyses in Basel. Milk samples from local milk production centres in northwest Switzerland of the states (cantons) of Aargau, Basel-Campaign, Basel-City, Solothurn, and Jura were analysed with β- and γspectrometry. On 2 May 1986, after the accident in Chernobyl, the frequency of the survey was intensified. On 4 and 5 May, radioiodine activity concentrations between 220 and 650 Bq/L 131I were measured. The milk from the mountainous region of the state of Jura showed lower values than in the states localised in the plain: 178 Bq/L 131I (4 May). In the milk distribution centres of Basel-City, the milk from the different regions had to be mixed in such a way that the population received milk with activities below 350 Bq/L. Due to its short half-life, the

applications will not be discussed further, because the analytes are not radionuclides.

hours, the samples are counted on an HPGe detector.

of 127I to 128I, which decays to 128Xe [31].

thousands of samples were analysed.

papers [31–33, 98].

138 Radiation Effects in Materials

Jura with 50 mm rain.

**5.1. Milk and milk products**

**5. Results from 35 years of food control**

**Figure 2. Results of the monitoring of milk from northwest Switzerland.** Notice the sharp peaks due to the Chernob‐ yl fallout. The 90Sr activity concentration shows a steady decline from 1981 to 2015.

We found much lower activity of 90Sr with a maximum value of 4.4 Bq/L on 11 March 1987 in Jura. In the Swiss Alps, the level reached 35 Bq/L. After 1988, the contamination of the milk from the canton of Jura reached a value of approximately 0.1 Bq/L. The present contamination of Swiss milk is highest in the Alpine regions of the states of Grison and Ticino, where the radiostrontium level is a factor 10 higher than in the rest of Switzerland (0.1–0.4 Bq/L), and radiocaesium reaches 9 Bq/L for the highest value (0.3–9 Bq/L) [34, 35].

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 hazelnuts.

#### **5.2. Wild-grown vegetables**

#### *5.2.1. Hazelnuts and other nuts*

**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 Basel.

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 value of 10 Bq/kg. After 1990, the contamination of hazelnuts in Switzerland and abroad remains under 10 Bq/kg; meanwhile, in Turkey, the contamination level was reduced much more slowly due to the higher contaminated soils (**Figure 3**).
