DOI 10.1007/s00217-005-0127-6

ORIGINAL PAPER

Petr Dvorak · Veronika Kunova · Katarına Benova

Exponential drop of radiocesium activity in mushrooms dueto the effect of acetic acid

Received: 29 April 2005 / Revised: 02 June 2005 / Accepted: 19 July 2005 / Published online: 18 October 2005C© Springer-Verlag 2005

Abstract The capability of vinegary pickle (2% solutionof acetic acid) as a decontaminant for mushrooms has beenstudied. The complete sporocarps of Xerocomus badius,Suillus luteus and Lepista saeve in dry weight, the nativestate and after defrosting were investigated. The mushroomsamples gathered in forest ecosystems were contaminatedby the post-Chernobyl radiocesium. The activity concen-trations of 137Cs were determined by the semiconductorgammaspectroscopy. It was proved that the reduction inactivity has been affected by the frequency of replacementof acetic acid. However, the number of replacements islimited due to a change of the mushroom consistency. Thevinegary pickle is already effective after the first treatment,i.e. the activity in the dry weight was reduced by 73%, andin the native state by 59%. The radiocesium activity followsan exponential curve with the exponents of 0.766 (the dryweight with the values exceeding the maximum permis-sible level of contamination), 0.266 (the dry weight withlow activities) and 0.040 (mushrooms in the native statewith the activities near the maximum permissible level ofcontamination) for the repeated effect of the fresh solutionof acetic acid.

Keywords Radioactivity . Foodstuffs preservation . 40K .137Cs . Gammaspectroscopy . Foodstuffs safety

P. Dvorak (�) · V. KunovaInstitute of Biochemistry, Chemistry and Biophysics, Faculty ofVeterinary Hygiene and Ecology, University of Veterinary andPharmaceutical Sciences Brno,Palackeho 1-3, 612 42 Brno, Czech Republice-mail: dvorakp@vfu.czTel.: +420-5-41562608Fax: +420-5-49250478

K. BenovaDepartment of the Environmental, University of VeterinaryMedicine Kosice,Komenskeho 73,041 81 Kosice, Slovak Republic

Introduction

The capabilities to remove the radionuclides from the food-stuffs were already studied in the 1960s for both domesticfoodstuffs preparation and foodstuffs industrial technolo-gies. The reason for this study was the fear of an increasingamount of radionuclides in the environment as a conse-quence of the airborne nuclear tests.

After the Chernobyl accident (1986), long-term radionu-clides such as 137Cs and 134Cs with a long-term radiationrisk factor were released into the environment. From thetotal amount of cesium released (i.e. 100%), different por-tions have penetrated into different types of food, of that50% in meat, about 30% in foodstuffs of plant origin, 14%in milk, etc. [1]. More than 15 years after this nuclear dis-aster, there are some locations with radiocesium presentboth in mushrooms and in the game meat with the valuesexceeding the maximum permissible level of contamina-tion of 600 Bq kg−1 137Cs and 134Cs for the basic exportedfoodstuffs according to the EU legislation. For air-driedmushrooms is limit of activity 137Cs 6000 Bq kg−1 [2].

The health risk for the population by intake of the con-taminated mushrooms might be particularly increased forpersons impaired by the other negative environmental fac-tors or for persons with affected immune system, never-theless it is necessary to seek possible reductions of theradiocesium activity in mushrooms. Some mushrooms in-cluding edible mushrooms cumulate a considerable amountof radionuclides [11]. Mushrooms growing on the territoryof the Central Europe are not only a bio-indicator of the en-vironmental radiocesium contamination, but they can alsobring a hygienic risk for the population. Radiocesium isdistributed unequally in the particular parts of mushroomswhile a higher radiocesium activity was found in mush-room caps [3, 10]. For the different types of mushrooms,there is a different capability of radionuclide cumulationfrom the environment [4]. This was proved by the fact thatthe increased 137Cs cumulation in Xerocomus badius is af-fected by norbadion A contained in a brown cap skin [5]. Itis assumed that the activity of radiocesium in mushrooms is

Eur Food Res Technol (2006) 222: 139–143

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related to their growth phase, similarly as for higher plants.During their growth, a total activity of 137Cs in such organ-isms is reduced [6]. From this point of view, the smallestsporocarps which are very often used for preservation arethe most hazardous.

Cesium is characterized by many physical–chemicalproperties similar to potassium. In a live organism, bothelements behave in the same way, and hence no methodexists for their mutual separation. Due to good water solu-bility, cesium is well and relatively uniformly absorbed anddistributed in the organism. Despite the fact that the con-centration of natural non-radioactive cesium does not differsignificantly both in mushrooms and in vascular plants, theactivity concentrations of137Cs in mushrooms were higherby one order. This discrepancy in behaviour can be ex-plained by the unbalance of the cesium and potassiumquantity in the ecosystems after nuclear accidents [7].

To reduce the activity of cesium in mushrooms, somemethods of mushroom preservation can be applied. Dry-ing, vinegary pickle and mushroom freezing belong to thebasic mushroom preservation methods. Drying is the oldestpreservation method. During mushroom drying, 80–90%of water evaporates and its weight is reduced by the samevalue. This means that radiocesium will be concentrated.Preservation by the vinegary pickle belongs to the mostpopular methods, hence the treated mushrooms in such away can be flexibly utilized. This method can be even usedfor meat marinating and for a certain reduction of radio-cesium activity. Brine salting is a less suitable method dueto a high salinity. However, soaking in 0.3% table salt so-lution can be used for a possibility to decrease the metallevels in Xerocomus badius [8]. Freezing of mushrooms isa very simple preservation method, however from the pointof view of maintaining a good mushroom consistency, it isless suitable.

Material and methods

The dried and homogenized Xerocomus badius and Suillusluteus sporocarps from the natural locations at Stare Ran-sko (The Czech-Moravian Highlands, CR), Strbske Plesoand Popradske Pleso (The High Tatra, Slovak Republic),Xerocomus badius in the fresh state from Stare Ransko

(The Czech-Moravian Highlands, Czech Republic) and de-frosted Lepista saeve coming from Dolnı Rozsıcky (TheCzech-Moravian Highlands, Czech Republic) were inves-tigated.

The activity concentrations of 137Cs a 40K were measuredby gammaspectroscopy with the Canberra MCA (DesktopInspector with an HPGe GC2020 semiconductor detector,20% efficiency and 1.8 keV resolution at 1.33 MeV). Thecomplete system was certificated by the Czech Metrolog-ical Institute (Certificate No. 911 – OL – Z 2888b/2003).The defrosted mushrooms and the fresh mushrooms weremeasured in the Marinelli beaker geometry with a vol-ume of 450 ml. The air-dried samples were measured inpolyethylene bottles with a volume of 200 ml. The min-imum detectable activity (MDA) for the Marinelli beaker(450 ml) and for 137Cs with the measurement time of 18 h(T=64 800 s) was 0.4 Bq kg−1, and for the polyethylene bot-tle (200 ml) 2.4 Bq kg−1. The Genie 2000 (Canberra) andGamat (PK-Servis Praha) software applications were used.

Each sample was measured for 137Cs and 40K activityconcentrations. Subsequently, a progressive change of the137Cs and 40K activity concentrations caused by the effect ofa 2% acetic acid solution was observed. The samples wereextracted in different time intervals, and after removingthe solution, they were again weighed and measured. Eachsample was extracted three to five times. The number ofreplacements of the fresh acetic acid solution was limiteddue to worsening of the mushroom consistency. The freshmushrooms and the defrosted mushrooms were immersedin fresh solution of acetic acid each 24 h. Due to a higheractivity of cesium, the interval of 2 h for one extractionat the air-dried mushrooms was selected. Before the firsttreatment in acetic acid, the mushrooms were immersedinto water to be swelled and then measured. The constanttemperature of 10 ◦C was kept during the complete processof preservation and even during storage.

In Tables 1–4, the particular activities and the combinedrelative standard uncertainties ua determined according tothe following formula [9] are shown

ua = (u2

E + u2p + u2

y + u2S + u2

ss + u2r + u2

t + u2A + u2

M

) 12

where the particular standard uncertainties are as follows:relative uncertainty for efficiency (uE), relative uncertainty

Table 1 The activity concentrations of 137Cs and 40K of Xerocomus badius mushrooms (Bq kg−1 dry wt.) during the extraction in 2%acetic acid solution, the input mushroom activity concentration was 6263 Bq kg−1 for 137Cs and 465 Bq kg−1 for 40K

Time t (h) Trial A Trial B137Cs 40K 137Cs 40K(Bq kg−1) ua (Bq kg−1) ua (Bq kg−1) ua (Bq kg−1) ua

0a 1253 3.4 465 4.9 1253 3.4 465 4.92 348 4.4 868 4.9 322 4.5 1046 4.94 54 10.9 1006 4.9 59 10.1 1082 4.96 13 31.4 1107 4.9 <2.4 1360 4.98 <2.4 1220 4.9 <2.4 631 4.910 <2.4 683 4.9 <2.4 889 4,9

aThe 137Cs activity concentration (Bq kg−1) after wetting in water and mushroom swelling

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Table 2 The activity concentrations of 137Cs and 40K of Suillus luteus (Bq kg−1 dry wt.) during the extraction in 2% acetic acid solution,the input mushroom activity concentration was 650 Bq kg−1 for 137Cs and 1124 Bq kg−1 for 40K

Time (h) Trial A Trial B Trial C137Cs 40K 137Cs 40K 137Cs 40K(Bq kg−1) ua (Bq kg−1) ua (Bq kg−1) ua (Bq kg−1) ua (Bq kg−1) ua (Bq kg−1) ua

0a 130 3.4 951 4.9 130 3.4 951 4.9 130 3.4 951 4.92 71 8.2 831 4.9 79 7.4 851 4.9 70 7.4 811 4.94 23 17.5 583 4.9 35 12.3 667 4.9 34 11.1 747 4.96 10 39 557 4.9 28 14 756 4.9 27 13.2 870 4.98 <2.4 960 4.9 21 18.3 588 4.9 20 16.7 530 4.910 <2.4 766 4.9 14 26.1 868 4.9 13 22.0 787 4.9

aThe radiocesium activity concentration (Bq kg−1) after wetting in water and mushroom swelling

Table 3 The activity concentrations of 137Cs and 40K in fresh mushrooms of Xerocomus badius (Bq kg−1) during the extraction in 2%acetic acid solution

Time (h) Trial A Trial B137Cs 40K 137Cs 40K(Bq kg−1) ua (Bq kg−1) ua (Bq kg−1) ua (Bq kg−1) ua

0 708 2.6 297 4.2 415 2.7 233 4.324 296 2.7 145 4.3 162 2.7 83 4.348 104 3.1 164 4.3 61 3.0 64 4.472 37 4.6 166 4.4 a a

168 a a a a

aA remarkable change in consistency of mushrooms appeared, and hence it was not possible to continue

Table 4 The activity concentrations of 137Cs and 40K for the defrosted mushrooms∗ (Bq kg−1) during the extraction in the solution ofacetic acid

Time (h) Trial A Trial s B Trial C137Cs 40K 137Cs 40K 137Cs 40K(Bq kg−1) ua (Bq kg−1) ua (Bq kg−1) ua (Bq kg−1) ua (Bq kg−1) ua (Bq kg−1) ua

Nativeweight

49 3.4 122 4.3 49 3.4 122 4.3 49 3.4 122 4.3

0a 28 4.2 169 4.3 27 4.3 143 4.3 43 3.4 126 4.324 14 8.3 229 4.3 17 7.5 228 4.3 19 5.3 154 4.348 12 6.3 97 4.4 b b

aThe juice released after defrosting was separated before measurementbA remarkable change in consistency of mushrooms appeared, and hence it was not possible to continue

for peak area (up), relative uncertainty for yield (uy), rela-tive uncertainty for time coincidence summing (us), relativeuncertainty for electronic stability (uss), relative uncertaintyfor time (ut), relative uncertainty for decay (ur), relative un-certainty for self-absorption (uA), and relative uncertaintyfor reproducibility (uM).

Results and discussion

Results are summarized in Tables 1–4 in which the re-duction of the activity concetration of 137Cs and 40K (inBq kg−1) together with the combined relative standard un-certainties ua are shown.

As seen from Tables 1–4 for all measured samples ofBoletus badius, Suillus luteus and Lepista saeve, the reduc-

tion of the 137Cs activity concentrations was proved by theeffect of the 2% acetic acid solution.

The reduction is also remarkable for the defrosted mush-rooms (Table 4) where the input cesium activity concentra-tion was not so high. The reason for a particular reduction ofthe cesium quantity before the process itself is in defrostingwhen cesium was transferred into the juice being released.A loss of the juice released due to defrosting reduced thecesium activity in mushrooms by 42% on average.

For the air-dried mushrooms, a reduction of the radioce-sium activity concentration depending on the duration ofthe acetic acid treatment and the frequency of the solutionreplacements is evident. This corresponds to the idea thatthe ions in a cell are replaced with the environment duringthe process due to osmotic pressure changes (Tables 1 and2). It can be also stated that the activity reduction due to

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the effect of acetic acid in 2-h time intervals (Tables 1 and2) is identical with the daily intervals (Table 3).

For the air-dried mushrooms (Xerocomus badius) withthe input 137Cs activity concentration of 1253 Bq kg−1 ex-ceeding the maximum permissible level of contamination(Table 1), the activity concentration was reduced after thefirst extraction by 73% on average. The curve of the reduc-tion in the radiocesium activity concentration versus thefrequency and the time of the extraction is characterizedby an exponential function (Figs. 1–3). The exponentialreduction of 137Cs is also accompanied by a change of the40K activity concentration. For the air-dried of Xerocomusbadius with the original 137Cs activity of 1253 Bq kg−1 (Ta-ble 1 and Fig. 1), we can observe the initial growth of 40Kcorresponding to a decrease of the 137Cs activity, howeverif the 137Cs activity concentrations reached the values nearthe tenths of Bq kg−1, a progressive reduction even for 40Kappeared. A significant growth of the 40K activity duringthe effect of acetic acid (Table 1) may be attributed to ahigher activity concentration of 40K in acetic acid. The ac-tivity concentration of 40K in the 2% solution of acetic acidwas 256 Bq kg−1. It can be assumed that the gradual elutionof 137Cs led to a moderate increase of 40K attributed to the2% solution of acetic acid. Only after a successive reduc-tion of the 137Cs activity concentration at a level of tenths ofBq kg−1, the 40K activity concentration was successivelyreduced (Fig. 1) due to the chemical equilibrium of theelements between mushrooms and the solution of aceticacid.

For the air-dried of mushrooms with a lower activity of137Cs (130 Bq kg−1) (Suillus luteus) (Table 2), the averageactivity concentration of radiocesium was reduced by 44%.A lower percentage of the radiocesium reduction for Suillusluteus compared to Xerocomus badius could be inducedby this kind of mushrooms. The trial was repeated threetimes (Table 2A–C) for the same dry weight sample withthe input activity concentration of 130 Bq kg−1 while theaverage percentage of the exponential drop of 137Cs wasaccompanied by a moderate polynomial increase of 40K(Fig. 2). For these samples, a direct relationship betweenthe reduction of 137Cs activity and a growth of 40K has notbeen proved (Fig. 2).

y= 1171 e-0.766x

I= 0.983

0

200

400

600

800

1000

1200

1400

0 2 4 6 8 10 12

t (hours)

Act

ivit

y of

137

Cs

(Bq

kg-1

)

137-Cs 40-K exponential (Cs-137)

Fig. 1 The exponential drop of the average activity concentrationof 137Cs (Bq kg−1 dry wt.) of Xerocomus badius, with a higher inputactivity of 1253 Bq kg−1

y= 115 e-0.266x

I= 0.990

y= 1.496x2 - 10.912x + 733.890 I = 0.321

0

100

200

300

400

500

600

700

800

900

0 2 4 6 8 10 12

t (hours)

Act

ivit

y of

137 C

s (B

q kg

-1)

137-Cs 40-K exponential (137-Cs) polynomial (40-K)

Fig. 2 The exponential drop of the average activity concentration of137Cs (Bq kg−1 dry wt.) of Suillus luteus, with a lower input activityof 130 Bq kg−1

y = 573 e-0.040x

I = 0.999

y = 230 e-0.018x

I = 0.866

0

100

200

300

400

500

600

700

0 10 20 30 40 50 60

t (hours)

Act

ivit

y of

137

Cs

(Bq

kg-1

)

137-Cs 40-K exponential (137-Cs) exponential (40-K)

Fig. 3 The exponential drop of the average activity concentrationof 137Cs (Bq kg−1 fresh wt.) of Xerocomus badius with 562 Bq kg−1

The average percentage of radiocesium reduction inXerocomus badius in the native state was also significant,i.e. −59%. For these mushrooms (Table 3), it was possibleto observe the identical exponential drop for both 137Csand 40K (Fig. 3). To achieve a more significant effect, thereplacement frequency of the acetic acid solution is crit-ical. By replacing the solution, the radiocesium activityconcentration can be reduced up to the minimum values.This effect of the solution coincides with the marinatingdata of meat in a vinegary pickle. Unfortunately, the num-ber of solution replacements is limited by the mushroomconsistency.

For defrosted Lepista saeve samples, we cannot exactlydescribe the nature of 40K activity changes. A probablereason is in a loss of extraction repeatability (Table 4) be-cause the solution was macerated and the mushrooms weredecomposed. This can be explained by the fact that thevinegary pickle treatment was already the second preser-vation procedure. The change in consistency by repeatingthe process has appeared even for Xerocomus badius inthe fresh state (Table 3), however, this effect was not asremarkable as for defrosted Lepista saeve.

We can conclude that the exponential drop of the ra-diocesium activity concentration has been the most re-markable for the air-dried of mushrooms with the activityexceeding the maximum permissible level of radioactive

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contamination (Fig. 1). This reduction was characterizedby the exponent of 0.766. For the dry matter with a loweractivity (Fig. 2), the value of the exponent was only 0.266.For fresh mushrooms, the value of exponent was 0.040(Fig. 3).

Conclusion

As seen from our results, the treatment of mushrooms in theacetic acid solution is one of the suitable methods to reducesignificantly the radiocesium activity concentration and toobserve the general principles of the mushroom preserva-tion. In compliance with the above described experimentalconditions, it can be stated that the 2% acetic acid solu-tion can simulate the standard preservation method with-out a significant change of their consistency. To achievea reduction of the radiocesium activity concentration, onetreatment cycle of the acetic acid solution is satisfactory.One treatment with the vinegary pickle is effective for boththe air-dried mushrooms (a reduction by 73%) and for thefresh mushrooms (a reduction by 59%). When the treat-ment cycles were repeated, the consistency deteriorated atthe defrosted mushrooms and at the fresh mushrooms whilethe dry matter has kept its steady consistency.

Because of the exponential nature of the activity reduc-tion affected by the 2% acetic acid solution, it can be rec-

ommended that, at the areas affected by the post-Chernobylradiocesium, the mushroom technology preservation withvinegary pickle should be applied while the pickle itselfshould not be consumed.

Acknowledgements This study was funded by the grant no.MSM6215712402 from the Ministry of Education, Youth and Sportsof the Czech Republic.

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