The Science o.[';he Total Environment, 105 (1991J 1-12 Elsevier Science Publishers B.V., Amsterdam

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Transfer of Chernobyl fallout radionuclides from feed to growing rabbits" cesium-137 balance G.A. Battiston", S. Degetto ~', R. Gerbasi a, G. Sbrignadello a'*, R. Parigi-Bini b, G. Xiccato b and M. C i n e t t o b Istituto di Chimica e Tecnologia dei Radioelementi, C.N.R., Area di Ricerca, Corso Stati Uniti, 4, 35020 Padova, Italy bIstituto di Zootecnica, Universita' di Padova, Via Gradenigo, 6, 35131 Padova, ltah' (Received May l lth, 1990; accepted June 24th, 1990)

ABSTRACT

Intake, excretion and retention of gamma-emitting radionuclide~ were asses-~ed in male rabbits fed a radioactive pelleted diet (~3~Cs = 858 Bq kg-~ as fed) containing 40% dehydrated alfalfa meal contaminated by Chernobyl fallout. In order to evaluate radionuclide retention, an experiment was carried out on 33 animals as follows: nine rabbits were slaughtered at the beginning of the trial, six were fed a radioactive diet for 42 days, six a radioactive diet for 21 days, six a radioactive diet for 21 days and a normal diet ( ~ C s = !!2 Bq kg-~ as fed) for the following 21 days and six a normal diet for 42 days. All the animals were housed in individual metabolism cages throughout the trial. AI~ faeces and urine were collected and analyzed separately and live weight and feed intake were measured on a weekly basis. At the end of the trial all the animals were slaughtered and the activities of net body and muscles were determined Cesium- 137, ~3,Cs, ~03Ru, ~0bRu, 12~Sb, ~0mAg and 4oK were measured by gamma spectroscopy. More than 85% of ingested cesium was excreted through faeces and urine (fecal ~> urinary) and the retained t~TCs in the carcass of the mote contaminated animals was only 3% of the total ingested. The concentration of total cesium in muscle reached a maximum value of 156 Bq kg- ~, much lower than the EEC guideline (600 Bq kg- t ), and the biological half-life for ~3~Cs was calculated to be ! I days. The feed-body accumulation factors were determined in net body and muscle. INTRODUCTION

After the nuclear accident in Chernobyl (USSR), heavy rainfall coincident with the passage of the radioactive cloud over Italy, caused, locally, high wet deposition of radionuclides [1]. These were subsequently found at elevated concentration in soil, grass and plants, particularly in roughage, vegetable and animal products. Several studies on the uptake, transfer, cycling, metabolism * Author to whom all correspondence should be addressed. 0048-9697/91/$03.50

© 1991 m Elsevier Science Publishers B.V.

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G.A. BATTISTON ET AL.

and retention of radionuclides for cattle, sheep and ewes, lambs, reindeer, cows and cow milk are reported in the literature [2], but very few data exist for the rabbit. With the aim of evaluating potential radionuclide transfer from contaminated feed to rabbit meat, a metabolism trial was conducted measuring the excretion and retention of radionuclides in growing rabbits [3]. EXPERIMENTAL

Feed, animals and feeding The experimental feeding lasted 42 days. Nine male rabbits (live weight 751 + 60 g) were slaughtered at the beginning of the ~xperiment in order to determine initial radionuclide activities. Twenty-four rabbits (initial live weight 765 + 67 g) were kept in individual metabolism cages and fed two pelleted diets: diet R was a radioactive feed (137Cs = 858 Bqkg -~ as fed) containing 40% dehydrated first-cut alfalfa meal, harvested in northeast Italy, highly contaminated by Chernobyl fallout; diet N was a normal feed (~~7Cs = 112 Bq kg -~ as fed) containing 40% dehydrated second-cut almost uncontaminated alfalfa meal. The rabbits were divided into four groups of six animals: Group R-R was fed diet R for 42 days; Group R was fed diet R for 21 days and then slaughtered; Group R-N was fed diet R until Day 21 and diet N for the following 21 days; Group N-N was fed diet N for 42 days. All diets were given ad libitum. Individual live weight and feed intake were measured weekly. All faeces and urine were collected individually; in addition, samples were collected for calculation of mean values for weeks 1-3 and 4-6. Average daily weight gain (38.2g), feed intake (140.0g), and conversion factor (3.66) were within normal ranges. At the end of the feeding period (21 days for Group R and 42 days for all other groups) the rabbits were slaughtered and the carca~cs frozen. After freezing, each carcass was divided into two equal parts, one was entirely ground in order to determine tota! body activity and the other was dissected to measure muscle activity.

Measurement of radioactivity The activities of ~37Cs, ~34Cs, 1°3Ru, J°6Ru, ~25Sb, ~°mAg and of natural 4°K in feeds, faeces, urine, carcasses and muscle were measured by gamma spectroscopy using, with standard geometry (Marinelli beaker or suitable plastic containers), a high-resolution (FWHM, 1.82 keV at 1.33 MeV; peak/Compton, 40/!; relative efficiency, 13.2%) PGT Ge(Li)detector (shielded by 10cm low-activity lead) linked to an appropriate data-acquisition system (8K ~Silena" MCA analyzer).

"I'R:kNSFER O r CHERNOBYL FALLOUT RADIONUCLIDES

Energy (a parabolic curve) and efficiency (a polynomial ,-'arve) calibrations were performed using suitable standards (QCY44 and a ~~-'Eu calibrated solution from Amersham International, UK) mixed with the appropriate rnat:,~ice:s. ~(!ounting times varied from ~ 50000 to 90000 s depending on the sample activity. The precision regarding statistical counting errors was always better than 10% at the 95% confidence level.

Sampling The nine animals slaughtered at the beginning of the experiment were divided into three groups of three rabbits each for preparation of carcass and muscle samples for analysis. The remaining animals were divided into four groups of six rabbits each. Carcass, muscle and excreta samples were obtained by combining material from two animals of each group. RESULTS AND DISCUSSION Chernobyl fallout contained both fission and activation products. Several beta- and gamma-emitting nuclides were also present but, in ti~e long-term, the dominating nuclide was 137Cs [1]. The measured activities cf both R and N pelleted feed, at the beginning, middle and end of the trial, are reported in Table 1. For diet R, ~37Cs appears to contribute most to the radioactivity, followed by ~34Cs and then ~°6Ru; for diet N, only ~37Cs and ~34Cs were above the detection limit. The activity of 4°K is reported as a control and is similar in both diets. At the end of the trial, the activities of the shorter half-life nuclides, ~aCs (2.06 years), I°~Ru (39.4 days), "~6Ru (366.5 days), ~'SSb (2.71 years) and TABLE I Radionuclide activity (Bq kg t as fed) of pelleted feeds (R. radioactive; N. normal} at the beginning, middle and end 01"the expet'iment Beginning

Middle

End

R

N

R

N

R

N

tWCs ~~4Cs io.~Ru "J~'Ru i.,sSb

858(5)" 383 (4) 55(10) 167(9) 22(7)

112(6) 42(7) ND" ND ND

857(5) 376(4) 38(I) 161(9) 22(7)

!12(6) 42(7) ND ND ND

856(5) 369(4) 26(I) 154(9) 21{7)

I i 2(6)

Iio., Ag

9(6)

ND

4°K 540(7) 503(7) "Analysis errors (%) in parentheses. hND, not detectable.

9(6)

540(7)

ND

503(7)

8(6)

540(7)

41(7) ND ND ND ND 503(7)

4

GA. BATTISTON ET AL. 1600 1400 1200 I000 \

I OR.N

I::1

60O 400

t'

I

I

I

!

2

3

4

5

6

Fig. !. Cesium-137 activity in dried faeces (Bq kg -t).

Ag (252.2 days), decreased, by physical decay, with respect to the activity registered at the beginning, as reported in Table 1. Uncontaminated drinking water was used throughout the experiment. Figures 1 and 2 show the variation of ~37Cs concentration in faeces and urine, respectively, during the 6-week trial. For Group R-R the very high level of radioactivity in faeces reached during the first week was maintained during successive weeks. A rapid decrease in radioactivity in faeces was observed for IlOm

25O

2OO

,5o

100

-0

'

r,

,

t

t

i

I

1

2

3

4

5

Fig, 2, Cesium-137 activity in urine (Bq k g - t ) ,

.A ,,I 6

TRANSFER OF CHERNOBYL FALl.OUT RADIONUCLIDES

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Group R-N on changing to diet N. A similar trend, with a delay of about 1 week due to the slower mineral metabolism, was noted for urine. Table 2 shows weekly data for radionuclide activity in faeces and urine, together with the averages for the first (Days 1-21) and second period (Days 22-42) of the trial. High concentrations of all radionuclides were observed in faeces, but only ~37Cs and ~34Cs were detectable in the urine. The activity of 4°K in excreta shows that this element is readily retained from feed, but it is mainly excreted through the urine. It appears that accumulation of cesium does not occur in order to satisfy a need for potassium; the 4°K activity in the different rabbit groups was almost constant in feed, faeces, urine, carcasses and muscle, whereas the cesium content (as ~37Cs activity) varied very widely, in the same matrices, according to the diet. The behavioral comparison between Cs and K can be seen from the 137Cs/4°K ratio, at equilibrium, observed in the various 'compartments' of the rabbit body at the end of the trial. The ~37Cs/40K ~'Jctivity ratio for faeces was 8.2 for Group R-R and 1.2 for Group N-N, while for urine it was 0.39 and 0.08, respectively. For muscle the ratio for Group R-R was 0.91 at the end of the tria!, whereas that for Group N-N was 0.19. A ratio of 1.8 was found for the liver of animals receiving highly contaminated feed, and 0.4 for the other groups. For the blood, a ratio of 1.23 was measured for Group R-R. For feed the ratio was 1.6 (diet R) and 0.22 (diet N). This ratio is descriptive of the different behavior of K and Cs and suggests small metabolic differences. For both Group R-R and N-N the ratio, in comparison with that of the respective feed, is of the same order of magnitude in body organs (liver, blood and muscle), whereas it is higher in faeces and lower in urine. The body organs (muscle and liver) present values slightly higher for Group N-N than Group R-R, which is tentatively ascribed to partially different chemical form of Cs in the diets (diet R, first-cut alfalfa meal; diet N, second-cut alfalfa meal). For faeces of Group R-N, 137Cs attains a peak value of 1416 Bq kg -~ in week 3 with a mean value, for the first 3 weeks, of 1306 Bq kg- t. On changing to a low-contaminated diet, a drastic decrease in ~37Cs activity is observed (78% in week 4 and 87% at the end c~f_.the.. tri'~!)..._. .As ,~,n~,-,°a....~,.,,,,,,,..,similar values were obtained for ~34Cs. It is interesting to note that ,~6Ru shows a similar decrease in faeces (84% on mean values), with a reduction of 76% after 1 week on diet N and of 89% by the end of the trial. A similar trend was also observed for ~25Sband ~0mAg. For urine a 63% decrease of the two Cs radionuclides can be seen in week 4 on going from diet R to diet N with an 82% decrease by the end of the trial. Data regarding 137Cs activity in the net body and muscle of the experimental groups are reported in Table 3. After 42 days of contaminated feed ingestion, the t~7Cs activity increased by a factor of 3 in the carcasses of Group

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G,A. BA'Iq'ISTON ET A i .

TABLE 2 Radionuclide activity in faeces and urine (Bq kg- z) of rabbits of Groups R-R, R-N and N-N during the 6 weeks of the trial Group R-R

Nuclide/week

Dried faeces

N-N

R-N

Urine

Dried faeces

Urine

Dried faeces

Urine

160(6) 228(6) 261(6) 183(5) 97(6) 57(6) 50(6) 69(6)

200(6) 177(6) 180(6) 179(6) 175(6) 177(6) 171(6) 174(6)

39(7) 46{,7) 51(6) 44(7) 35(6) 37(6) 39(6) 41(6) 16(6) 20(6) 23(5) 18(6) 16(61 ! 5(6) ! 7(6) ! 7(6)

~'Cs ! 2 3 Mean (!-3) 4 5 6 Mean (4-6)

1259(6)" 1366(6) 1373(6) !~364(6) 1448(6) i 399(6) 1455(6) 1447(6)

166(6) 233(6) 252(6) 207(6) 203(6) 199(6) 194(6)

i 242(6) ! 392(6) 1416(6) ! 306(6) 3 ! 2(6) 198(6) 191(6) 230(6)

! 2 3 Mean (!-3) 4 5 6 Mean (4-6)

564(6) 606(6) 625(6) 568(6) 622(6) 640(6) 625(6) 605,6)

73(6) 104(6) il i(5) 85(6) 89(61 86(6) 83(6) 82(6)

572(6) 625(6) 633(6) 544(5) 177(6) 85(6) 83(6) 95(61

70(6) i O1(6) !17(5) 77(6) 43(61 24(6) 21 (6) 29(6)

91(6) 80(6) 82(6) 75(6} 77(61 77(6) 72(6) 7516)

I 2

395(6) 346{9)

~< I

Transfer of Chernobyl fallout radionuclides from feed to growing rabbits: cesium-137 balance.

Intake, excretion and retention of gamma-emitting radionuclides were assessed in male rabbits fed a radioactive pelleted diet (137Cs = 858 Bq kg-1 as ...
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