Study of radiocesium contamination from Chernobyl accident in samples of black blueberry jams

More than 30 years after the Chernobyl accident, foodstuff based on black blueberries (Vaccinium myrtillus) with relevant 137Cs activity concentrations are still found in the European Union market. Recently, mass media reported that food products based on black blueberries produced in UE were rejected by Asian markets because the 137Cs activity concentration was greater than 100 Bq kg-1. It is known that Ukraine, Belarus and Russia are great exporters of black blueberries: there is a strong suspicion that the berries are collected also from the most radio-contaminated areas of these countries and introduced in UE markets. For this reason, about 40 samples of black blueberry preserves as jams, marmalades, stewed fruits were analysed with high resolution gamma spectrometry to measure 137Cs and 134Cs activity concentration. All the food preparations of the study have been collected in supermarkets and in local stores of northern Italy. 134Cs was less than minimum detectable activity in all samples, as expected following its half-life. On the other hand, 137Cs activity concentration was widely variable among samples: the minimum, mean and maximum concentration were 1, 54 and 162 Bq kg-1, respectively. The activity concentrations found in these products were corrected for the radioactive decay and reported to the same date. The activity concentration in fruits used for preserves was calculated from fruit percentage content reported on the product label. In fruits used for marmalades, jams and stewed fruits, 137Cs activity concentration up to 230 Bq kg-1 was found. In a sample of blueberries in syrup, 137Cs activity concentration in blueberries was 450 Bq kg-1. From statistical analysis and contamination data of European soil, it is clearly seen that the contamination from Chernobyl accident is still relevant in some forest ecosystems and its transfer to some vegetables must be taken in account. Organic and non-organic jams show no signifi cant difference in terms of mean 137Cs concentration. However, a potential multimodal distribution is observed for organic products, highlighting the possibility of fruit harvesting in areas with different 137Cs soil concentration. The results of this study are aimed to expand the current knowledge on the distribution of 137Cs in black blueberry products, allowing health organizations to improve the absorbed dose budget from raw berries-based food.

Hence, although 137 Cs contamination decreased in many agricultural products, it is still currently present in spontaneous mushrooms, in berries and in wild animals' meat because of the persistent contamination of forest ecosystems. By the way, in recent years the consumption of blueberries is continuously growing, also because berries are considered rich in nutraceutical substances.
The black blueberry plant (Vaccinium myrtillus) belongs to the ericaceous family and is characterized by a root system called "rhizome". The rhizome grows up horizontally in the fi rst, organic layer of the soil, with a few centimetres thickness and extending in distance also for some meters. It is made up of "endotrophic mycorrhiza" that have a high mobilization capability and high capability of absorption of mineral salts from the soil, similarly to many species of mushrooms. This property is common to all ericaceous plants and may sometimes give rise to high 137 Cs concentration values [5].
In Italy, the black blueberry plant grows spontaneously in the Alps and in part of the Apennines, in acid and loose soils; the fruits are usually collected by hand. Moreover, in Italy blackberry cultivation is almost completely family-run, for domestic consumption: industrial cultivation of blackberry is almost absent; they are indeed present in northern Europe,

Material studied
The jars of jams and other foodstuffs based on blackberry were bought in supermarkets and local stores in Veneto and

Methods and technique
Sample preparations and analysis were done in the CNR-  Table 2. The detector is installed inside a lead well, internally coated with a copper and cadmium sheets to achieve a very low environmental background. The software Genie2000® (Canberra TNE) was used for spectral acquisition and quantitative spectral analysis. Nuclide library used is Nucleide Lara LNHB (2018).
The effi ciency calibration for the measurement geometrical confi guration (jar 50 ml) was calculated with multi-gamma certifi ed standard solutions (QCY48 e QCYB40 by Amersham) in the same geometrical confi guration as the measurements. The results were corrected for "matrix effect" considering the different density and composition of the samples with respect to the standard solution used for effi ciency calibration. The effi ciency of the measurement system is periodically checked through inter-calibration tests promoted by National Physics Laboratory (Teddington, UK). Acquisition times for the analysis of 137 Cs were variable from one sample to another and were manually chosen with the aim to achieve a statistical counting uncertainty (1 Standard Deviation SD) in the 137 Cs photopeak at 661,7keV of less than 5%. The Limits of Detection (LOD) were estimated at 95% confi dence level.

Jams, marmalades and stewed fruits
Measurements results and activity concentrations of 137 Cs in blackberries are reported in Table 3. As predictable, 134 Cs was not detected in any sample (always under the detection limits of 1Bq kg -1 ). We can reasonably argue that 137 Cs present in the samples is attributable mostly to the Chernobyl fallout. In fact 137 Cs soil inventory due to weapon tests in the atmosphere is meanly about 2kBq m -2 [1]. For what concerns Fukushima accident in Europe the contribution to total 137 Cs might be not relevant [2,10].
The mean 137 Cs activity concentration of 36 samples of blueberry jam bought in supermarkets and local stores was 54 ± 50 (1 SD) Bq kg -1 and the maximum activity recorded was 162Bq kg -1 . Percentage content of fruits declared on product label for all products (organic and non-organic) was in the range 50%÷60%, except two products declaring respectively a fruit content of 102% and 110%. The mean fruits content for organic and non-organic products is very similar (64% and 60%, respectively).
The 137 Cs content in blackberries was calculated starting from the fruit content declared on the label (Table 3, column 5), resulting a mean and maximum 137 Cs activity in the fruits of 85 ± 72 (1 SD) and 234Bq kg -1 , respectively (Table 4).
To evaluate if cultivation methods could infl uence 137 Cs content, the whole marmalade dataset was divided in two sub-samples: one of "organic" jams (19 samples), the other one of "non-organic" jams i.e. jams without any information about fruits cultivation (17 samples). The results of the descriptive statistics are reported in Table 4. Mean 137 Cs activity concentration was higher in organic jams (98) respect to nonorganic jams (70) but standard deviation and maximum value were almost equal.
Data distributions of the two sub-samples are reported in Figure 2. It is worth to be noted that for organic products and fruits the distribution is probably multimodal: about half samples have 137 Cs activity concentrations less than 90Bq kg -1 , similarly for organic products and for non-organic products.
Fruit frequency distribution for organic product shows a possible mode between 140 and 150Bq kg -1 .
The two sub-sample distributions were compared through parametric and non-parametric statistical tests. distributions that show large skewness [11]. As can be noted in Table 5, both parametric and non-parametric statistical tests suggest to not reject H0, leading to the conclusion that organic This means that the test result for 137 Cs content in fruits must be considered cautiously.

Other blackberry-based foodstuff
Also a canned fruit sample "Frutta Sciroppata" VIS (IT-SO) bought in supermarket was analysed (not reported in Table   3). The product is made of blackberry fruits in sugar syrup.
For the good as it is (fruits submerged in syrup), the activity Table 4: Descriptive statistics of the 137 Cs content in blueberries jams, after separation of organic and non-organic products.  concentration measured was 168±5Bq kg -1 . Since this is a quite high 137 Cs concentration, on the reasonable hypothesis that radiocesium was initially contained in the berries and not in the sugar syrup, an attempt was made to calculate the initial activity concentration in the berries. At fi rst, the berries were manually separated from the syrup. An amount of the canned berries was then drained off and repeatedly rinsed in milliQ water, with the aim to remove possibly all the syrup from the berries.

All jams Organic jams Non-organic jams
The 137 Cs activity concentration for the washed berries, for the syrup and for the rinsing water were measured and results are reported in Table 6. From these data and from the weight of the analysed samples, the initial activity concentration of 137 Cs in the berries (A * ) was re-calculated assuming that 137 Cs were initially present only in the berry using equation 1: where A b and m b are the 137 Cs activity concentration and mass of rinsed berries, respectively, and A s and m s are the activity and the mass of the syrup analysed separately. For completeness, also the washing water was collected and analysed: the activity concentration was 5÷1Bq kg -1 . The results are reported in Table   6. The value obtained from this trial is obviously only semiquantitative, as it was not possible to collect and analyse all washing water and separation of syrup and berries was not 100% effi cient. Anyhow the result of the activity concentration of 137 Cs in the berries is quite high: 456Bq/kg: this supports the thesis that many lots of blueberries come from highly contaminated regions.

Discussion
The results of the activity concentration of 137 Cs in blackberry jams found in this work are higher than those reported in recent literature [12,13]. Letho, et al. [14] reports 137 Cs activity concentration in berries of black blueberry (V.  (Table 7); however, due to the numerosity of chemical and biological processes involved, the wide variability of these data is well known.

Myrtillus) in southern Finland
As 35 years from the Chernobyl accident last, the authors wonder which are the growing area of black blueberries with 137 Cs activity concentrations in the range 200÷500Bq kg -1 .
However, in the products' label, the fruits' geographical origin is never reported, as it is not compulsory by law.
Considering a mean activity concentration in black blueberries of about 100Bq kg -1 (fresh weight) (the same level of the samples analysed in this paper), and considering a range of soil to berry transfer factors of 0.005÷0.008m 2 kg -1 (fresh weight), we can argue an estimate of 137 Cs soil inventory of about 12.5÷20Bq m -2 . As can be seen from the map in Figure 1, areas with levels of contamination between 10 and 40kBq m -2 are very wide: these areas are found in Italy, in Scandinavia, in central Europe and in Russia. Following our hypothesis, it is reasonable to expect that on EU market black blueberries with activity concentration higher than 100Bq kg -1 are in circulation and traded. Moreover, considering the data reported in Table 1, it is reasonable to assume that many lots of berries over 600Bq kg -1 (maximum reference level for import in UE) could also be traded on the EU market.

Conclusions
Following the Chernobyl accident, 137 Cs activity concentrations measured in food preparations based on black blueberries are to date still relevant. This is explicable observing the soil contamination spatial extension in Europe and in Russia. On the basis of the results submitted in this paper and of the maps cited above, the authors believe possible that on the EU market, fruits with 137 Cs activity concentration higher than 600Bq kg -1 are still introduced and in circulation.
The analysis of food preparations with organic label showed mean 137 Cs activity concentrations of the same level or a little higher than those without any organic certifi cation. On the other hand, organic labels do not comprise any radioactivity analysis, neither in raw material, nor in food products.
From the results shown in this paper, the extension of the contamination in Europe and in Russia, the wide variability